The Complete Works of Aristotle
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Logic & Organon
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The first work of the Organon. Aristotle categorizes all things that can be said into ten fundamental categories, establishing a framework for predication and ontology.
Part I–IV: Introductory distinctions
1–3 1a1–1b24
Homonyms, synonyms, and the said-of / in-a-subject grid
Distinguishes homonyms (things sharing a name but not a definition), synonyms (sharing both name and definition), and paronyms (derived names like 'grammarian' from 'grammar'). Introduces the fundamental distinction between what is 'said of' a subject (predicated universally — e.g., 'man' is said of Socrates) and what is 'in' a subject (an attribute inhering in it — e.g., whiteness is in a body). These two relations generate four combinatorial classes of entity: said-of and in (e.g., knowledge-of-grammar), said-of but not in (e.g., man), in but not said-of (e.g., this particular whiteness), and neither (e.g., this individual horse). The framework is Aristotle's earliest attempt at ontological classification.
4 1b25–2a10
The ten categories enumerated
Lists the ten categories — the ten highest genera under which everything that can be said falls: substance (ousia), quantity (poson), quality (poion), relation (pros ti), place (pou), time (pote), position (keisthai), state/having (echein), action (poiein), and affection (paschein). Every simple term signifies something in one of these categories. Substance answers 'what is it?', while the other nine are ways of being attributed to substances. This tenfold scheme provides the skeleton for the rest of the treatise and reappears throughout Aristotle's philosophy.
Part V–IX: The ten categories examined
5 2a11–4b19
Substance — primary and secondary
The longest and most important chapter — on substance (ousia). Primary substances are individual things (this man, this horse): they are neither said-of nor in anything else. Secondary substances are species and genera (man, animal): they are said-of primary substances. Primary substance is most truly substance because it underlies everything else: without individuals, nothing else could exist. Key properties of substance: it has no contrary, admits no degrees (one substance is not 'more substance' than another), and — most distinctively — it is capable of receiving contraries while remaining numerically the same (Socrates can be pale, then tanned, remaining Socrates throughout).
6 4b20–6a35
Quantity — discrete and continuous
Quantity (poson). Aristotle distinguishes discrete quantity (number, speech) from continuous quantity (lines, surfaces, bodies, time, place). Discrete quantities have no common boundary at which parts join; continuous quantities do. Quantities have no contraries (nothing is the contrary of 'three feet long') and do not admit of degrees. The most distinctive property of quantity is that it admits the predicates 'equal' and 'unequal' — only quantities can be called equal or unequal.
7 6a36–8b24
Relation and correlatives
Relation (pros ti): things said to be 'of' something else or 'than' something else — the double is double of something, knowledge is knowledge of something. Correlatives are simultaneous by nature: if there is a master, there is a slave; if a half, a whole. Aristotle gives a revised definition: a relative is that for which being is the same as being somehow related to something. He discusses whether substance can be relative (parts of secondary substances seem relative — a head is 'of' a body) but decides primary substance itself is never relative.
8 8b25–11a38
Quality — four species
Quality (poion): four species. (1) Habits and dispositions — lasting states like knowledge or virtue vs. easily displaced conditions like warmth. (2) Natural capacities and incapacities — the runner's speed, the sick person's inability to resist cold. (3) Affective qualities — sweetness, bitterness, color, warmth — and the temporary 'affections' (pathē) they produce. (4) Shape and form — triangle, square, straight, curved. Quality admits contraries (justice vs. injustice) and degrees (one thing is whiter than another). The distinctive feature: things are called 'such and such' (like, unlike) in respect of their qualities.
9–10 11b1–12a25
Action, affection, position, state, place, time
The remaining categories — action (cutting, burning), affection (being cut, being burned), position (sitting, standing), state/having (being armed, being shod), place (in the marketplace), and time (yesterday) — are treated more briefly. Aristotle notes that these are evident from what has been said and passes to the post-predicaments. Chapter 10 transitions by distinguishing four types of opposition: correlatives, contraries, privation/possession, and affirmation/negation.
Part X–XV: Post-predicaments
10–15 11b17–15b32
Post-predicaments — opposites, priority, simultaneity, motion, having
Five topics supplementing the categories. (1) Opposites: four types distinguished — correlatives (double/half), contraries (good/evil), privation/possession (blindness/sight), affirmation/negation (he sits / he does not sit). Contraries may have intermediates; contradictories never do. (2) Priority: five senses distinguished — temporal, logical (what does not convert), ordinal, evaluative (the more honorable is 'prior in nature'), and causal. (3) Simultaneity: by nature (things that imply each other) and by time. (4) Motion: six kinds — generation, destruction, increase, diminution, alteration, change of place. (5) 'Having' (echein): multiple senses — having a quality, having a quantity, having on (clothes), having in (grain in a jar), etc. The post-predicaments are less systematically unified but fill out the conceptual toolkit.
On Interpretation (De Interpretatione)
Examines the relationship between language and logic, especially how propositions can be true or false and how they are structured.
Chapters 1–6: Signs, nouns, verbs, and propositions
1–3 16a1–16b25
Words as conventional symbols; nouns and verbs
Words are conventional symbols (kata sunthēkēn) of mental impressions — which themselves are natural likenesses of things. Written words symbolize spoken words, spoken words symbolize thoughts. Aristotle defines the noun (onoma): a spoken sound significant by convention, whose parts have no independent meaning, and which carries no temporal reference. The verb (rhēma) additionally co-signifies time — 'recovers' indicates present action while 'recovered' indicates the past. Verbs alone do not make an assertion; they must be combined with nouns. Important for later linguistics: the distinction between semantics (what words signify) and assertion (what sentences do).
4–6 16b26–17b16
Sentences, assertions, and affirmation vs. denial
A sentence (logos) is a significant spoken sound whose parts are individually significant but not as affirmations or denials. Not every sentence is an assertion — prayers, for instance, are sentences but are neither true nor false. An assertion (apophansis) is a sentence that is true or false: either an affirmation (kataphasis — predicating something of something) or a denial (apophasis — separating something from something). A single assertion concerns one subject-predicate pair; compound sentences involve multiple assertions joined together. Introduces universal/particular distinction in predication.
Chapters 7–14: Logical relations of propositions
7–8 17b16–18a12
Universal, particular, and the square of opposition
Universal, particular, and indefinite statements. When universal terms are predicated universally ('every man is white') we get universal affirmatives and negatives; when not universally ('some man is white') we get particulars. Contrary vs. contradictory opposition: 'every man is just' and 'no man is just' are contraries (both can be false); 'every man is just' and 'not every man is just' are contradictories (exactly one is true). Indefinite statements ('man is white') behave logically like particulars.
9 18a28–19b4
The sea-battle and future contingents
The famous 'sea-battle' chapter — the most discussed passage in ancient logic and philosophy of language. The question: is it already determinately true or false that there will be a sea battle tomorrow? If so, fatalism seems to follow — everything happens of necessity. Aristotle's solution (much debated) seems to hold that while the disjunction 'there will or will not be a sea battle' is necessarily true, neither disjunct taken individually is yet determinately true or false. This preserves the law of excluded middle (the disjunction is necessarily true) while restricting bivalence — denying that each singular future contingent is already determinately true or false. The chapter has generated vast literatures in logic, metaphysics, and theology.
10–14 19b5–24b9
Modal propositions — necessity, possibility, contingency
Simple and compound propositions; how to negate complex statements correctly. Modal propositions — necessity, possibility, impossibility, and contingency. Aristotle establishes logical relationships among modalities: what is necessary is actual, what is actual is possible. He arranges modal propositions into a 'modal square' of opposition analogous to the categorical square. Discusses the compatibility of possibility with necessity and impossibility, and whether 'possible' means 'not impossible' or 'not necessary'. Chapter 14 critiques the view that contraries of beliefs correspond to contraries of facts — the contrary of a true belief is not a belief in the contrary, but a denial of the same thing.
Prior Analytics
The systematic study of syllogistic reasoning — the foundation of formal logic. Aristotle defines the syllogism and surveys all valid and invalid forms.
Book I: The syllogism
1–7 24a10–29b25
The syllogism defined and the three figures
Aristotle defines his terms: a premise (protasis) is a statement affirming or denying one thing of another; a term (horos) is that into which a premise is resolved (subject or predicate); a syllogism (sullogismos) is a discourse in which, certain things being stated, something different from what is stated follows necessarily. Introduces the three figures of syllogisms based on the arrangement of the middle term: first figure (middle is subject in one premise, predicate in the other), second figure (middle is predicate in both), third figure (middle is subject in both). Demonstrates which combinations of premise-types in each figure yield valid conclusions — the foundation of all formal logic, which remained the dominant logical framework for over two thousand years until Frege's Begriffsschrift (1879) inaugurated modern predicate logic.
8–22 29b29–40b16
Modal syllogisms — necessity and possibility
Modal syllogisms: Aristotle extends the system from assertoric (plain fact) premises to premises involving necessity and possibility. Examines all valid moods when one or both premises are modified by necessity, possibility, or contingency. The analysis is extraordinarily complex — mixing pure necessity syllogisms, pure possibility syllogisms, and mixed-modal arguments across all three figures. Some results remain controversial among commentators. This section is the most technically difficult part of the Organon and anticipates modern modal logic by two millennia.
23–46 40b17–52a38
Conversion, reduction, and indirect proof
General conclusions about syllogism. All valid reasoning can ultimately be expressed in syllogistic form. Conversion of propositions (simple conversion, conversion per accidens) and reduction of imperfect syllogisms to perfect ones in the first figure. Further topics: indirect proof (proof by contradiction), arguments from a hypothesis, and the general requirements for finding premises to prove any given conclusion. Chapter 46 discusses the quality of terms (affirmative/negative) and how negations affect syllogistic reasoning.
Book II: Properties and uses of syllogisms
1–15 52b1–64b27
True conclusions from false premises; circular proof
True conclusions from false premises — shows how valid syllogistic form can yield true conclusions even from false premises (though not vice versa: valid form with true premises always yields truth). Circular proof (proving A from B and B from A) is examined and shown to be severely restricted. Proof by contradiction: how to convert such an argument into a direct syllogism and vice versa. Error in reasoning: how mistakes arise from taking false premises or using invalid forms. The precise conditions under which error is possible in each figure.
16–26 64b28–69b36
Fallacies, argument by example, and the enthymeme
Begging the question (petitio principii): assuming what you need to prove, whether openly or through convertible terms. The fallacy of the false cause (non causa pro causa): inserting a premise that does not actually contribute to the conclusion. Argument by example (paradeigma) as rhetorical induction. The enthymeme as a syllogism from signs or likelihoods (with probabilistic rather than certain premises). Chapter 23 discusses induction (epagōgē) as the passage from particulars to a universal and shows how it can be expressed syllogistically.
27–32 69b37–47a22
A method for constructing syllogisms
A practical method for constructing syllogisms for any given thesis. Aristotle provides a systematic procedure: collect all the predicates, subjects, and negations relevant to the terms in question, and search among them for a suitable middle term. This 'pons asinorum' of syllogistic gives the student a mechanical technique for finding proofs. Concludes with observations on the types of sciences that use different forms of proof, and on the figures best adapted to mathematical, natural, and dialectical reasoning.
Posterior Analytics
The theory of scientific knowledge (episteme): how demonstration from first principles produces genuine understanding, as opposed to mere opinion.
Book I: Demonstrative science
1–6 71a1–75a37
Demonstration from first principles
All teaching and intellectual learning proceeds from pre-existing knowledge. Scientific demonstration (apodeixis) is a syllogism that produces genuine knowledge (epistēmē): its premises must be true, primary, immediate, better known than, prior to, and causally explanatory of the conclusion. Knowledge is distinguished from opinion and from mere true belief by this causal-explanatory structure. Aristotle introduces axioms (common principles like non-contradiction) and theses (principles proper to a science — both definitions and hypotheses). A science cannot demonstrate its own first principles; they must be grasped by a different faculty.
7–18 75a38–81b9
The genus restriction and 'the why' vs. 'the that'
The genus restriction: each science studies a single genus or domain, and cannot borrow demonstrations from another genus (no 'crossing of kinds'). Arithmetic cannot prove geometrical truths using arithmetical principles, though there are subordinate sciences (optics to geometry, harmonics to arithmetic) that borrow principles from higher sciences. Discusses the distinction between 'that' something is the case (hoti) and 'why' (dioti) — a demonstration of the 'why' gives the cause, while the 'that' may use effects or remote causes. Universal demonstrations are superior to particular ones because they reveal causes at the highest level of generality.
19–34 81b10–89b20
Against infinite regress; undemonstrable first premises
Can there be an infinite chain of demonstrations, or must we reach unprovable first principles? Aristotle argues against infinite regress: both ascending (ever-more-universal predicates) and descending (ever-more-specific subjects) chains must terminate. Therefore there exist immediate, undemonstrable premises. Ignorance can arise from privation (never knowing) or from false syllogism. Knowledge of the universal is more exact and higher than knowledge of the particular. Sciences with fewer principles (arithmetic) are more exact than those with additional principles (geometry adds magnitude). Discusses essential attributes (those belonging to a thing in itself) and the structure of definitions within demonstrations.
Book II: Definition and first principles
1–10 89b21–97a6
Four questions of inquiry; definition and demonstration
Four questions of scientific inquiry: (1) whether a thing has an attribute (the 'that'), (2) why it has it (the 'reason why'), (3) whether the thing exists, and (4) what it is (its essence). All four reduce to seeking the middle term — the cause. Definition (horismos) states the 'what it is' (to ti esti) — the essence. Can definition be demonstrated? Aristotle's subtle answer: definition itself is indemonstrable (it is not a syllogism), but demonstration can 'display' what a definition says by using the definiens as the middle term. The difference is one of logical arrangement, not content.
11–18 94a20–99a16
The four causes in demonstration
The four causes in demonstration: the formal cause appears as the definition (the middle term gives the 'what'); the efficient cause appears as what initiated the process; the final cause as that for the sake of which; the material as the necessary conditions. How to discover the correct middle term: divide the genus, find the differentiae, and organize them properly. Discusses how the same effect can have different causes in different subjects, and how frequent vs. rare events (eclipses vs. individual thunderbolts) relate to scientific explanation.
19 99b15–100b17
Nous — intuitive grasp of first principles
The crucial final chapter: how are first principles themselves known, if not by demonstration? They are grasped by nous (intuitive intellect/intellectual intuition). The process: sense-perception yields memory; repeated memories of the same thing yield experience (empeiria); from experience, the universal 'settles in the soul'. Nous is more accurate and more authoritative than demonstration because it grasps the very premises from which demonstration proceeds. Thus the foundation of science is not itself scientific in the demonstrative sense — it is a higher, non-discursive intellectual grasp.
Topics
A manual for dialectical reasoning — argumentation that proceeds from reputable opinions (endoxa) rather than first principles. Used in debate and philosophical inquiry.
Book I: Introduction to dialectic
1–18 100a18–108b33
Dialectic, endoxa, and the four predicables
Aristotle distinguishes dialectical reasoning (from reputable opinions, endoxa) from demonstrative reasoning (from true and primary principles), eristic reasoning (from what appears reputable but is not), and paralogistic reasoning (from premises proper to a special science but badly used). The purpose of the treatise: a method for constructing arguments on any proposed problem from endoxa. Three uses: intellectual training, casual conversation, and philosophical science (by puzzling through aporiai (philosophical impasses) from both sides, we can more easily discern truth). Introduces the four predicables — definition (what the thing is), property (unique but non-essential attribute), genus (shared nature), and accident (neither unique nor part of the essence) — which organize all possible predications and thus all possible dialectical questions.
Books II–III: Accidents and comparisons
II–III 109a34–120a7
Topoi for accidents and a fortiori arguments
A rich catalogue of topoi (argument-places or strategies) for attacking or establishing that something is an accident of a subject. Book II offers general topoi: consider whether what is said of the genus holds of the species; consider opposites and correlatives; check for self-refutation. Book III focuses on topoi of comparison (the 'more and less'): if something is 'more' likely to have a property and does not have it, then what is 'less' likely does not have it either (a fortiori arguments). These comparative topoi remain fundamental to informal reasoning and legal argumentation.
Books IV–V: Genus and property
IV–V 120a15–139a19
Topoi for genus and property
Book IV: topoi for attacking and defending assignments of genus. A genus must be predicated of its species in the category of substance (in the 'what is it?' question). Check that the assigned genus is genuinely more universal, that the species falls under it, that differentiae are appropriate, and that the genus itself is truly a genus (not an accident or property of the subject). Book V: topoi for property (idion). A property must belong to the subject alone and convert with it (if it is human, it is capable of grammar; if capable of grammar, it is human). Tests: does the alleged property belong at all times? Is it stated in prior and better-known terms? Is it proved using the thing defined (circular)?
Books VI–VII: Definition
VI–VII 139a24–155a37
Topoi for definition and identity
The most elaborate section — definition is the most important predicable because it reveals the essence. Book VI: a correct definition must (1) state the genus and differentia, (2) be clear (avoid metaphors and ambiguity), (3) use terms prior and better-known to the definiendum, (4) be unique to the thing defined (convert with it), (5) not be circular. Topoi for attacking definitions: show the definiens is too broad, too narrow, uses obscure terms, gives non-essential features, or applies to things outside the genus. Book VII: briefly on whether two things are 'the same' or 'different' (identity), since definition claims identity between definiendum and definiens.
Book VIII: Dialectical practice
VIII 155b3–164b19
Practical advice for dialectical debate
Practical advice for the dialectical 'game' as practiced in the Academy and Lyceum. How to order your questions so the respondent does not see where the argument is heading. How to secure premises: use induction, analogy, accepted opinions, or concealment of intent. How to handle premises when you are the answerer: distinguish what is reputable, what is true, and what is relevant. When to grant, deny, or draw distinctions. Advice on training: practice both roles, start with easy problems, and master the standard arguments. Concludes the Topics by claiming to have provided a complete method for dialectical argumentation on any subject.
Sophistical Refutations
A catalogue of fallacious arguments used by sophists to win debates through deception. Often regarded as Book IX of the Topics.
Single work
1–9 164a20–170b11
Six fallacies dependent on language
Sophistic is the appearance of wisdom without the reality — and the sophist is one who makes money from this apparent wisdom. A sophistical refutation (elenchus) appears to refute but does not actually do so. Aristotle classifies thirteen fallacies into two groups. Six depend on language (in dictione): (1) equivocation (homōnumia — the same word in different senses), (2) amphiboly (ambiguous sentence structure), (3) combination (sunthesis — running words together changes meaning), (4) division (diairesis — separating what should be combined), (5) accent (prosōidia — differences in breathing or pitch change meaning), (6) form of expression (schēma lexeōs — grammatical form misleading about ontological category). Each is explained with examples drawn from sophistic practice.
10–19 170b12–177b33
Seven fallacies independent of language
Seven fallacies independent of language (extra dictionem): (1) accident — inferring that what is true of a subject is true of its accident; (2) simpliciter / secundum quid — ignoring qualifications; (3) ignoratio elenchi — proving something other than the point at issue; (4) consequent — affirming the consequent; (5) begging the question (petitio principii) — assuming the conclusion among the premises; (6) false cause (non causa pro causa) — treating an irrelevant premise as essential; (7) many questions — combining multiple questions into one to trap the respondent. For each, Aristotle explains the mechanism of deception: which logical principle the fallacy appears to satisfy while actually violating.
20–33 177b34–184b8
Solutions to each type of fallacy
Solutions to each type of fallacy. The general strategy: identify which of the thirteen types is being deployed, then expose the specific logical flaw. For linguistic fallacies, draw the distinction that the argument trades on. For extra-linguistic fallacies, show which logical principle is being violated. Specific solutions are given for each class with examples. The work concludes with Aristotle's famous claim of originality: before him, rhetoric was taught but there was nothing at all on syllogistic reasoning — he had to discover the whole art from scratch. He compares his achievement to founding a new discipline and asks for the reader's gratitude for what has been discovered and pardon for what remains undiscovered.
Natural Philosophy
Physics
The foundational work of natural science. Aristotle examines nature, motion, causation, space, time, and the infinite — establishing the conceptual framework for all natural inquiry.
Book I: Principles of nature
1 184a10–184b14
Method — from what is known to us toward what is known by nature
Methodological opening: in every domain of inquiry we must proceed from what is more knowable and clearer to us toward what is more knowable and clearer by nature. The whole (a confused mass) is what we first grasp perceptually; analysis breaks it into its principles and elements. Thus natural science must begin from the general and proceed to the particular — from 'this is a body' to the precise principles constituting it.
2–4 184b15–187b7
Critique of monists and pluralists
Survey and critique of predecessors. The monists (Parmenides, Melissus) who posit one immovable being: their position eliminates natural science entirely. The pluralists (Anaxagoras, Empedocles, the atomists): they posit more than one principle but face problems about how many and what kind. Aristotle argues that principles must be contraries (since change is between opposites) and that there cannot be infinitely many (science requires finite first principles).
5–9 188a19–192b4
Three principles: form, privation, and matter
Aristotle's own solution: nature requires exactly three principles — two contraries (form and privation) and an underlying substratum (matter). This dissolves the Parmenidean puzzle about how what-is can come from what-is-not: the subject persists through the change, losing one contrary (privation) and gaining the other (form). Thus coming-to-be is not from absolute non-being but from a qualified non-being — the matter that lacks the form. Nature is identified with form rather than matter. Matter is the 'out of which'; form is the 'into which'; privation is the 'from which'. This triad structures all subsequent natural philosophy.
Book II: Cause and nature
1–2 192b8–194b15
Nature defined as internal principle of motion
Nature (phusis) defined: an internal principle (archē) of motion and rest belonging to a thing primarily and in virtue of itself, not incidentally. Natural things differ from artifacts in having their principle of change within themselves (a stone falls by nature; a bed does not grow). Nature is identified both with matter (the underlying stuff) and with form (the shape and definition) — but Aristotle argues form has a better claim, since a thing is more truly what it is when it has achieved its form. Distinguishes the physicist from the mathematician: both study forms, but the physicist studies forms as inseparable from matter.
3 194b16–195b30
The four causes
The celebrated doctrine of the four causes (aitiai): (1) the material cause — that out of which a thing is made and which persists (bronze of a statue); (2) the formal cause — the definition, essence, or pattern (the ratio 2:1 of the octave); (3) the efficient cause — the primary source of change or rest (the father of the child, the adviser of the action); (4) the final cause — that for the sake of which (health is the cause of walking). The same thing can have all four causes, and the same cause can be cited at different levels of generality. This fourfold causal framework is Aristotle's most influential contribution to the methodology of natural science.
4–6 195b31–198a13
Chance and spontaneity as incidental causes
Chance (tuchē) and spontaneity (to automaton) are incidental causes operating in the sphere of things that happen 'for the sake of something.' When an outcome that could have been intended occurs without intention — a man goes to the market and happens to meet his debtor — this is chance. Spontaneity is the broader category (it applies to animals and even natural events); chance applies only to agents capable of deliberate choice. Neither chance nor spontaneity is a true 'cause' in the primary sense; they are names for incidental conjunctions of genuine causal series.
7–9 198a14–200b8
Nature acts for an end; hypothetical necessity
Nature acts for an end (final causation in nature). Aristotle argues against both pure mechanism (Empedocles' 'survival of the fittest' suggestion) and pure chance, insisting that natural regularities — teeth growing sharp in front and broad in back, the spider spinning its web — cannot be explained without purpose. Necessity in nature is hypothetical, not absolute: if a saw is to cut, then necessarily it must be made of iron — but the iron is for the sake of cutting, not the cutting for the sake of the iron. The form and final cause coincide: what something is (form) is the same as what it is for (end).
Book III: Motion and the infinite
1–3 200b12–202b29
Motion defined as actuality of the potential
The definition of motion (kinēsis): the actuality (entelechia) of what exists potentially, insofar as it is potential. When the buildable, insofar as buildable, is being actualized — that is building (motion). Motion is incomplete actuality — it is the actualization of a potentiality that is still being actualized, not yet fully achieved. Motion exists in the thing moved, not in the mover. The mover and moved are in contact during motion. This definition is notoriously difficult and was the subject of intense commentary in antiquity and the middle ages.
4–8 202b30–208a23
The infinite — potential but never actual
The infinite (apeiron). Aristotle reviews the arguments for and against actual infinity, then introduces his own solution: the infinite exists potentially but never actually. One can always take more (in counting, in dividing a line), but an actually completed infinity never exists all at once. The infinite by addition never exceeds any assigned magnitude; the infinite by division never reaches an indivisible minimum. Infinity is not a substance but an attribute of magnitudes, numbers, and time. This potential infinity is sufficient for mathematics (which needs only 'as large as you please') without the paradoxes of actual infinity.
Book IV: Place, void, and time
1–5 208a27–213a10
Place as the boundary of the containing body
Place (topos). Aristotle rejects the identification of place with matter, form, or the interval between the boundaries of a body. His definition: place is the innermost motionless boundary of the containing body — the inner surface of the surrounding medium. Thus the place of a boat in a river is defined relative to the whole river (which is motionless as a whole), not relative to the flowing water immediately around it. Place is neither larger nor smaller than the thing in it. Every natural body has a natural place (earth tends downward, fire upward) which explains natural motion.
6–9 213a12–217b28
Arguments against the void
Arguments against the void (kenon). Aristotle denies that empty space exists, either as a separate dimension or interspersed among bodies. Key argument: in a void there would be no reason for a body to move in one direction rather than another (no natural places), and no reason for motion to stop (no resistance) — hence bodies would either not move at all or move infinitely fast. He also argues against atomist void by showing that compression, rarefaction, and interpenetration of bodies can be explained by change of quality rather than gaps between atoms.
10–14 217b29–224a17
Time as the number of motion
Time (chronos). Aristotle defines time as the number of motion with respect to the before and after — time is the countable aspect of change. A famous but debated passage suggests that time requires both motion and a counting soul: if there were no soul to count, there would be motion but not time in the sense of a measure — though whether Aristotle means time is genuinely mind-dependent or merely that counting requires a counter remains contested among interpreters. The 'now' (to nun) is not a part of time but a boundary between past and future, analogous to a point on a line. Time is continuous because motion is continuous. Whether time is the same everywhere, the relationship between time and the soul, and whether time could exist without change — all are explored.
Book V: Types of motion
1–6 224a21–231a17
Alteration, growth, and locomotion distinguished
Categories of change (metabolē): change in general divides into coming-to-be (from non-being to being), perishing (from being to non-being), and motion (kinēsis) proper — which occurs only between positive states. Motion divides into three kinds according to three categories that admit of contraries: motion in quality (alteration), motion in quantity (growth and diminution), and motion in place (locomotion). There is no motion in substance, relation, action, or affection. Unity and diversity of motions: when are two motions 'the same'? Aristotle distinguishes numerical, specific, and generic unity of motion.
Book VI: Continuity and motion
1–10 231a21–241b20
Continuity, indivisibles, and Zeno's paradoxes refuted
A continuum (sunechēs) cannot be composed of indivisibles: points cannot make a line, instants cannot make time, because adjacent indivisibles would either coincide (and not produce extension) or have something between them (contradicting adjacency). Everything that moves is divisible; there is no first instant of motion nor a first part moved. Refutation of Zeno's paradoxes: the Dichotomy (one must cross infinitely many half-distances) is solved because both distance and time are infinitely divisible — one crosses infinite subdivisions in correspondingly infinite subdivisions of time. The Achilles, the Arrow, and the Stadium are each refuted by the same analysis of continuity.
Book VII: Mover and moved
1–5 241b24–250b7
Everything moved is moved by something
Everything in motion is moved by something — there is no self-motion in the strict sense. Demonstration: if a body moves, either the whole moves the whole (impossible — then it both moves and is moved in the same respect) or a part moves the rest, and that part must itself be moved by something. Proportionality of force, resistance, and speed: if force A moves body B with speed C over distance D in time E, then the same force moves half of B at double the speed (or over double the distance in the same time). But this proportionality does not hold at all ratios — below a threshold, the force is insufficient to produce motion at all.
Book VIII: The eternal first mover
1–6 250b11–260a19
Motion is eternal; an unmoved mover is required
Has motion always existed, or did it begin? Aristotle argues motion is eternal: if it began, the beginning was itself a change, which requires a prior motion — infinite regress. Similarly it cannot cease. There must therefore be at least one eternal motion and an eternal mover. Survey of types of movers: self-movers (animals) are not truly primordial because their self-motion is initiated by environment. There must be a first mover that is itself unmoved — otherwise we face an infinite regress of movers, which explains nothing.
7–10 260a20–267b26
Circular locomotion and the indivisible first mover
The first motion is circular locomotion: it is the only motion that can be continuous, uniform, and eternal (since rectilinear motion must reverse direction). The heavenly spheres exhibit this eternal circular motion. The first unmoved mover has no magnitude (is not a physical body) because no finite body can supply infinite power, and an infinite body is impossible (proved in Book III). This mover is indivisible and without parts; Aristotle presents it as the explanatory source of cosmic motion rather than as a body occupying a literal spatial location. This is the Unmoved Mover — the metaphysical apex of Aristotle's natural philosophy, developed further in Metaphysics XII.
On the Heavens (De Caelo)
Cosmology and the structure of the universe. Aristotle argues for a finite, eternal, spherical cosmos with Earth at the center, and introduces the fifth element (aether).
Book I: The cosmos and its elements
1–4 268a1–271b26
The fifth element — aether and circular motion
The cosmos is a finite, complete whole — 'complete' meaning it contains all body and all the dimensions of body. Aristotle introduces the fifth element, aether (also called the 'first body'), whose natural motion is circular rather than rectilinear. Since circular motion has no contrary, the celestial body is ungenerated, indestructible, and subject to neither growth, alteration, nor decay. The superlunary realm is thus of a fundamentally different nature from the four terrestrial elements. The argument proceeds from the principle that every simple body has a single natural motion, and that circular motion belongs to no terrestrial element.
5–12 271b26–283b22
The cosmos is one, unique, and eternal
The cosmos is one and unique — the possibility of many worlds (kosmoi) is excluded because all the matter of each element is already contained within this cosmos. The cosmos is also eternal: it is ungenerated (never came into being) and indestructible (will never cease to be). Aristotle engages extensively with the Timaeus, arguing against Plato's claim that the cosmos was generated (even if Plato means this 'for didactic purposes'). Key argument: whatever is generated is also destructible; whatever is indestructible was never generated. Extended discussion of necessity, possibility, and eternity in cosmic context.
Book II: Celestial motions
1–9 283b26–291a28
Celestial spheres and the divine heavenly bodies
The heaven (ouranos) moves eternally and without effort — its motion is natural and requires no compulsion. The sphere is the primary shape in nature. Aristotle explains why there are multiple celestial spheres revolving in different directions: the sphere of the fixed stars revolves from east to west; the sun, moon, and planets have additional motions from west to east. The stars are not self-propelled but embedded in their spheres. They are composed of aether and are alive and divine — the heavenly bodies are 'the best things,' furthest from mere matter.
10–14 291a29–298a20
Earth is spherical and stationary at the center
The Earth is spherical and stationary at the center of the cosmos. Proofs of sphericity: (1) lunar eclipse — Earth's shadow on the moon is always curved; (2) the stars visible change as one travels north or south; (3) heavy matter naturally converges toward the center, producing a sphere. Aristotle gives the Earth's circumference as about 400,000 stades; because the stade varied across regions and periods, the estimate cannot be translated into a single modern value with confidence and is considerably too large by later standards. Earth does not rotate (arguments from projectile motion and falling bodies). The heavenly bodies are arranged by distance: Moon, Sun, planets, fixed stars. Brief treatment of the sizes and relative distances of the celestial bodies.
Book III: The four terrestrial elements
1–8 298a24–307b24
The four terrestrial elements and natural place
Below the moon, four elements (earth, water, air, fire) constitute all terrestrial bodies. They are generated from each other through transformation — unlike aether, they are mutable. Each has a natural place: earth at the center, water above earth, air above water, fire at the periphery of the sublunary realm. Their natural rectilinear motion (downward for heavy, upward for light) is evidence against the atomists' void, since without natural places there would be no natural motion. Critiques Plato's reduction of elements to geometric solids (triangles) in the Timaeus.
Book IV: Heavy and light
1–6 307b28–313b22
Absolute heaviness and lightness
Heaviness and lightness are absolute properties, not merely relative (contra Plato and the atomists). Earth is absolutely heavy (moves toward the center from any position); fire is absolutely light (moves away from the center toward the periphery). Water and air are intermediate — each is heavy relative to what is above it and light relative to what is below. The elements seek their natural places, and when they arrive they are at rest. Aristotle rejects the atomist explanation of weight as a function of density alone: shape, void content, and density are insufficient to explain why fire always rises.
On Generation and Corruption
Analyzes coming-to-be (genesis) and passing-away (phthora), alteration, growth, the interaction of elements, and the eternal cycle of elemental transformation.
Book I: Coming-to-be and alteration
1–5 314a1–322a33
Coming-to-be vs. alteration; growth and contact
Distinguishes absolute coming-to-be (genesis haplē — a new substance emerges) from alteration (alloiōsis — a substance persists but changes in quality). Critiques atomism: the atomists reduce all change to locomotion of indivisibles through void, but this cannot account for qualitative change or the real unity of compounds. Coming-to-be requires that something comes from its contradictory (non-being in a qualified sense). Growth (auxēsis) is a distinct type of change — not mere addition but an increase in the substance's own matter throughout all its parts. Contact and action require bodies to have surfaces, ruling out mathematical indivisibles as physical constituents.
6–10 322a34–328b22
Action, passion, mixture, and the four contraries
Action and passion (poiein/paschein): things interact because they are similar enough (same genus) yet dissimilar in form. The agent assimilates the patient to itself. Mixture (mixis) is distinguished from mere juxtaposition (synthesis): true mixture produces a new uniform substance whose components are 'preserved in potentiality' but not in actuality — unlike in aggregates, where components remain actually distinct. Introduces the four fundamental tangible contraries — hot/cold, wet/dry — as the principles underlying the elements. These two pairs will generate the four elements through their combinations.
Book II: The elements and eternal generation
1–5 328b26–333b3
Elements from paired contraries; elemental transformation
The four sublunary elements are constituted by pairs of contraries: fire = hot + dry; air = hot + wet; water = cold + wet; earth = cold + dry. Elemental transformation occurs when one contrary is overcome: fire (hot+dry) loses its dryness and gains wetness → becomes air (hot+wet). Two contraries are easier to change; the most difficult transformation is between elements sharing no qualities (fire↔water, earth↔air), which requires both contraries to change. Aristotle also considers compounds of elements and argues that in real compound bodies (flesh, bone, etc.) the elements are present 'potentially' — not actually persisting as discrete pockets.
6–11 333b4–338b19
The sun's motion drives eternal generation
Generation of elements and compounds is eternal because the sun's annual motion along the ecliptic alternately heats and cools the earth, driving a perpetual cycle of transformation. The efficient cause of generation and corruption in the sublunary world is the sun's oblique revolution — its approach brings heat and generation, its recession brings cold and corruption. This eternal cyclical process mirrors the eternal circular motion of the heavens. Final chapter discusses necessity and 'that for the sake of which' in natural processes: coming-to-be is necessary hypothetically (given the end), and the eternal recurrence of generation is itself necessary.
Meteorologica
Phenomena between the heavens and Earth: comets, the Milky Way, weather, rivers, seas, earthquakes, and mineralogy. Book IV's authenticity is sometimes disputed.
Book I: Celestial and atmospheric phenomena
1–14 338a20–349b10
Two exhalations; comets, Milky Way, rain, hail
The domain of meteorology: phenomena occurring in the region between earth and the stars — involving the two 'exhalations' (anathymiaseis). A dry, warm exhalation from earth and a moist, cool exhalation from water rise and are acted upon by celestial heat. Shooting stars, meteors, and the aurora are ignitions of the dry exhalation in the upper atmosphere. Comets are likewise dry exhalations ignited below the celestial sphere (not celestial bodies). The Milky Way is a permanent concentration of the dry exhalation along a particular band of sky. Lower phenomena: clouds form when moist exhalation is cooled and condenses; rain falls when clouds are further chilled; dew and frost are ground-level condensation; hail forms from rapid freezing of raindrops.
Book II: Waters and winds
1–6 353a32–365a13
The sea, rivers, and underground waters
The sea: its origin, saltiness, and why it does not overflow despite receiving all rivers. The sea is not a source of rivers (rivers originate from condensed moisture in mountains). The sea's saltiness comes from the admixture of dry exhalation — as moist vapor evaporates, the dry residue concentrates. Rivers: their sources, why some are perennial and others seasonal. The inhabitable world and the distribution of land and sea. Underground waters and thermal springs explained by subterranean exhalations and heat.
7–9 365a14–370a33
Earthquakes, winds, and the twelve named winds
Earthquakes (seismoi): caused by dry, smoky exhalation trapped underground. When large quantities of this pneuma seek an exit, the earth shakes. Explains why earthquakes follow calm weather (the exhalation has stayed below instead of escaping into air), why they occur more at night, and why coastal and porous regions are most vulnerable. Winds: the dry exhalation flowing horizontally constitutes wind. The twelve named winds and their compass positions. Etesian winds explained by the seasonal melting of northern snows which produces cooling and pushes moist exhalation southward.
Book III: Violent weather
1–6 370a34–378b5
Thunder, lightning, whirlwinds, and the rainbow
Thunder and lightning: the dry exhalation, enclosed within clouds, is violently squeezed out and ignites — this ignition is lightning, and the noise of the expulsion is thunder. We see lightning before hearing thunder because sight is faster than hearing. Thunderbolts: intensely concentrated lightning that strikes the earth. Whirlwinds (typhōnes), firewinds (prēstēres), and hurricanes (ekphniai) are all varieties of the dry exhalation twisted by wind or ignited in different configurations. Optical phenomena: the rainbow, halos, mock suns, and rods of light — explained by reflection of sight from moisture in the air at specific angles. Aristotle's account of the rainbow (three colors, specific angular conditions) is remarkably observational.
Book IV: Properties of bodies
1–12 378b10–390b22
Tangible properties, concoction, metals, and minerals
A systematic chemistry of tangible properties: hot and cold are active (they produce effects); moist and dry are passive (they receive them). The processes these produce: concoction (pepsis — transformation by heat into a good state), inconcoction (raw, underdone), ripening, boiling, roasting. Putrefaction (sēpsis) is destruction by an external cold of an object's proper heat. Solidification and melting: some things solidify by cooling (water→ice), others by drying (clay→pottery). Metals: formed from the moist exhalation trapped underground and congealed by cold. Minerals: formed from the dry exhalation compressed and solidified. Iron, gold, and various stones briefly discussed. This book anticipates later chemical thought.
On the Soul (De Anima)
Aristotle's psychology: the soul is the form of a living body. He analyses the soul's faculties — nutrition, sensation, imagination, reason, and desire.
Book I: Survey of predecessors
1 402a1–403b19
The soul as the noblest object of inquiry
The study of the soul (psuchē) ranks among the most honorable inquiries, both for its exactness and for the nobility of its subject. Methodological difficulties: what kind of thing is the soul — substance, quality, or quantity? Is it divisible or indivisible? Are all souls of the same species, or does each kind of living thing have a different kind of soul? The soul's affections (emotions, perceptions, thoughts) seem to involve the body — they are 'enmattered formulae' (logoi enuloi). Hence the physicist and the dialectician study the soul differently: the physicist looks at the material conditions, the dialectician at the formal definition. The correct definition must include both matter and form.
2–5 403b20–411b30
Critique of predecessors on the soul
Systematic critique of predecessors. Those who defined soul by motion (Democritus: soul-atoms moving rapidly; Plato's self-mover in Timaeus and Laws) — but the soul need not itself be in motion to cause motion. Those who defined soul as a harmony of bodily elements (Empedocles, the Pythagoreans) — but a harmony is a ratio or blend, not a mover, and different parts of the soul would be different harmonies, which is absurd. Those who defined soul as a number (Xenocrates) or as composed of elements (Empedocles: like knows like) — these confuse the soul's cognitive capacity with its ontological constitution. None of these accounts adequately explains how the soul is the cause of life, motion, and cognition together.
Book II: Definition and basic faculties
1–3 412a1–415a13
The soul as first actuality of a natural body
The soul defined: the first actuality (entelechia hē prōtē) of a natural body that has life potentially — i.e., an organic body. As the form/actuality of the body, the soul is not separable from it (just as the shape of a wax seal is not separable from the wax). The soul is 'that by which we live, perceive, and think primarily.' Levels of actuality: possessing knowledge (first actuality / hexis) vs. actively contemplating (second actuality / energeia). The soul is first actuality — like knowledge possessed but not currently exercised. Faculties of soul hierarchically ordered: nutritive (plants+animals+humans), sensitive (animals+humans), rational (humans alone). Each higher faculty presupposes all lower ones.
4 415a14–416b31
The nutritive soul — growth, nutrition, reproduction
The nutritive soul (threptikon): the most basic and universal psychic capacity, shared by all living things from plants upward. Its functions: nutrition (trophe — maintaining the organism), growth (auxēsis — increasing it), and reproduction (genesis — producing another like itself). Reproduction is the most natural function: every living thing strives to participate in the eternal and divine by producing offspring of its own kind. Food is contrary to the organism (cold nourishes hot), but in being concocted it becomes like it. The nutritive faculty is the form; food is the matter; the body nourished is the substrate.
5–12 416b32–424b18
Perception — receiving form without matter
Perception (aisthēsis): the soul receives the sensible form without the matter — as wax receives the impression of a signet ring without the iron or gold. Perception is a kind of alteration: the sense organ is potentially what the perceived object is actually (potentially colored, potentially hot). Each sense has its own proper object: sight→color, hearing→sound, smell→odor, taste→flavor, touch→tangible qualities. Detailed treatment of each: sight operates through a transparent medium (to diaphanēs) activated by light; hearing through air set in motion; smell, taste, and touch through direct or mediated contact with their objects. The sense organ must be in a mean state (neither too hot nor too cold) to discriminate both extremes.
Book III: Higher faculties
1–3 424b22–429a9
Common sense, imagination, and phantasia
There is no sixth sense beyond the five (proven because the five collectively exhaust the possible sensory media). The 'common sense' (koinē aisthēsis) — not a sixth sense but the primary sense faculty's ability to perceive common sensibles (magnitude, shape, number, motion, rest) that are accessible to more than one modality, and to discriminate between objects of different senses (e.g., that what is white is also sweet). Imagination (phantasia): intermediate between perception and thought — it is the capacity to have mental images (phantasmata) even when objects are absent. Phantasia is not perception (it occurs without objects), not opinion (it has no truth-value commitment), and not simple combination of the two — it is a motion produced by active perception that persists after the object is gone.
4–8 429a10–432a14
Active and passive intellect; nous is immortal
Intellect (nous): the capacity to think universals and essences. The intellect before it thinks is 'nothing actually' — like a blank writing tablet on which nothing is yet written. It must be unmixed with the body (otherwise it would be limited to a particular quality and could not know all forms). The active/passive intellect distinction (nous poiētikos / pathētikos): the passive intellect is like matter (can become all things); the active intellect is like the agent cause (makes all things actual), analogous to light which makes potential colors actual. The active intellect is 'separable, unmixed, and impassible' — it is 'essentially actuality' and 'alone is immortal and eternal.' The claim sits in sharp tension with the hylomorphic definition of soul in Book II (the soul as form of the body, inseparable from it), and this unresolved tension is precisely what made III.5 the most contested passage in all of Aristotle, generating enormous commentary in the Arabic, medieval Latin, and modern traditions.
9–13 432a15–435b25
Desire, the practical syllogism, and animal motion
Desire (orexis) as the cause of animal motion: the soul moves the body not by intellect alone (contemplation does not issue in action) but by desire directed toward a perceived or imagined good. Practical intellect (combined with desire) calculates means to desired ends. The practical syllogism: a universal premise (e.g., 'dry food is good for humans'), a particular premise ('this is dry food'), and the conclusion is action (eating). Thus reason, imagination, and desire cooperate in producing movement. Touch is the most fundamental sense: without it, no animal can exist; the other senses exist 'for the sake of well-being.' Touch and taste are necessary for life; sight, hearing, and smell are for a better life.
Parva Naturalia
A collection of nine short treatises extending the De Anima into sense, memory, sleep, dreams, life, and respiration.
Disputed authorshipOn Breath (De Spiritu) is in the traditional corpus but generally considered post-Aristotelian.
On Sense and Sensibilia (436a–449b)
All 436a1–449b3
Physiology of the five senses
Extends De Anima's treatment of perception into detailed physiological and physical analysis. Examines how the five senses operate: what their proper objects are, what physical processes mediate between object and organ, and how the sense organ is materially constituted to receive forms. Color is defined as the limit of the transparent in a determinate body; sound as the motion of air struck by a hard body against a hard surface. Discusses the unity of the sensory soul — how a single faculty discriminates white from sweet — and whether simultaneous perception of different objects is possible. Questions about the minimum perceptible threshold and whether sense-perception is instantaneous or requires time.
On Memory and Reminiscence (449b–453b)
All 449b4–453b11
Memory, mental images, and deliberate recall
Memory (mnēmē) is always of the past — one cannot 'remember' the present or the future. Memory requires a mental image (phantasma) that functions as a likeness (eikōn) of the thing remembered. Animals with a sense of time can have memory; those that perceive only the present cannot. Reminiscence (anamnēsis) is distinct: it is the deliberate recovery of a past cognition through a chain of associations — by similarity, contrariety, or contiguity. Reminiscence is a kind of inference ('I perceived X after Y, so from Y I can recover X'). Only humans can reminisce because it requires deliberate search. Melancholic temperaments are both more prone to vivid memories and more troubled by inability to control the associative process.
On Sleep and Waking (453b–458a)
All 453b11–458a32
Sleep as incapacitation of the primary sense-organ
Sleep is a temporary incapacitation of the primary sense-organ (the heart or its analogue). It results from the evaporation produced by food: warm vapors rise from the stomach to the head, are cooled, descend to the heart region and cool the blood around it, suppressing perceptual activity. Waking occurs when digestion is complete and the blood returns to its proper heat. Sleep is for the sake of preservation (rest restores the sensory faculty). All animals that perceive also sleep — but plants, which merely nourish, do not. The boundary between sleeping and waking is not sharp: drowsiness is an intermediate state where perception is weakened but not abolished.
On Dreams (458a–462b)
All 458a33–462b11
Dreams as residual sense-movements
Dreams (enupnia) are not perceptions (the senses are inactive in sleep) but residual motions (kinēseis) persisting in the sense-organs from prior perceptual activity. These after-images and residual movements, undisturbed by fresh sensation, become vivid and appear real — the dreaming person mistakes phantasmata (mental images) for perceptions because the critical faculty (the common sense) is inactive. Dreams are not sent by the gods (they are natural phenomena, and they occur in all animals, not only humans). The bizarre combinations in dreams are explained by the disordered mixing of residual movements from different past experiences, just as reflections in troubled water distort images.
On Divination in Sleep (462b–464b)
All 462b12–464b18
Skepticism toward prophetic dreams
Are prophetic dreams possible? Aristotle is skeptical of divine causation but offers three naturalistic explanations for apparently prophetic dreams: (1) coincidence — given the vast number of dreams, some will inevitably resemble future events; (2) the dream is a sign of bodily states that the dreamer cannot perceive while awake (incipient diseases produce physiological changes that appear symbolically in dreams); (3) the dream is a cause — having dreamed of doing something, one is more likely to do it (the dream initiates a train of action). Excitable and melancholic persons have more vivid dreams and thus more apparent 'hits' — but this is a matter of temperament, not divine favor.
On Length and Shortness of Life (464b–467b)
All 464b19–467b9
Vital moisture, heat, and animal longevity
Why do some animals live longer than others? Life is maintained by a balance of vital moisture and heat. Large animals tend to live longer because their greater bulk of moisture takes longer to be dried out by their vital heat. Plants can live very long because they continually renew themselves (new shoots replace old). Insects and small animals live briefly because they have little moisture. The hottest and moistest animals — those with blood, living in water — tend to be longest-lived. Birds live longer than their size would predict because their feathers conserve heat and moisture. The discussion connects animal physiology to the physics of elemental transformation.
On Youth, Old Age, Life and Death (467b–470b)
All 467b10–470b5
The heart's vital heat as source of life
The source of life is vital heat (thermotēs) located in the heart (or the analogous central organ in bloodless animals). Life is the maintenance of this heat; death is its extinction. Youth is the period when vital heat is strong and moisture abundant; old age is progressive drying and cooling. Death occurs when the inner fire is finally 'quenched' — either violently (disease, injury) or naturally (when fuel runs out). The heart is the first organ to live and the last to die. Nutrition sustains the vital fire by providing fuel (food → blood → heat). Plants and animals alike depend on this same fundamental mechanism: the balance of internal fire and its nutrient moisture.
On Respiration (470b–480b)
All 470b6–480b21
Breathing cools the heart's vital heat
The function of breathing: to cool the vital heat around the heart and prevent it from becoming excessive. Inhalation brings cool air to the lungs; the blood passing through the lungs is cooled; this tempered blood returns to the heart. Fish accomplish the same cooling through gills and water. Animals that neither breathe nor have gills (insects) are cooled by their small size and thin membranes. Breathing and heartbeat are coordinated: the heart's pulsation pumps blood, and respiration regulates the temperature of that blood. Detailed accounts of how suffocation, drowning, and asphyxiation occur — all involve the failure to cool the vital heat, which then consumes the body's moisture and extinguishes itself.
On Breath / De Spiritu (481a–486b)
All 481a1–486b4
Connate pneuma as a psycho-physiological principle
Treats pneuma (breath or vital spirit) as a key bodily factor in life and motion, especially in connection with reproduction and the soul's operations. The work overlaps strongly with themes found in On the Movement of Animals and Generation of Animals, but its terminology and argument are not usually taken to be Aristotle's own. Read as part of the later Peripatetic tradition, it is valuable evidence for how Aristotelian themes about soul, heat, and bodily mediation were developed after Aristotle, rather than as a secure statement of Aristotle's personal doctrine.
Biology
History of Animals
The most extensive biological work, covering anatomy, behavior, diet, reproduction, and ecology of hundreds of animal species. Books VII and X are sometimes considered later additions.
Book I: Distinctions and parts
1–17 486a5–495b27
Parts, ways of life, and human anatomy as reference
Foundational distinctions among animals. They differ in their parts (some have lungs, some gills; some have blood, some do not), their way of life (land, water, air), their activities (some swim, some fly, some burrow), and their character (some are fierce, some gentle, some cunning). Parts are either homogeneous (homoiomerē — blood, bone, fat, flesh, where any portion is the same as any other) or non-homogeneous (anhomoiomerē — a face, a hand, where the part is not the same as the whole). Animals with blood (enhaimata) roughly correspond to vertebrates; bloodless animals (anhaima) to invertebrates. Begins systematic description of human external anatomy as a reference point for comparative study.
Book II: Anatomy of blooded animals
1–17 496a4–506b2
Comparative anatomy of blooded animals
Detailed comparative anatomy of blooded animals (vertebrates). The head: mouth, teeth (their variety in carnivores, herbivores, omnivores), tongue, palate, ears (external pinnae in some, simple openings in others), nostrils, eyes. The trunk: neck (present in those with lungs, absent in fish), chest, stomach, intestines. Internal organs: heart (the first organ to form and the seat of vital heat), liver (large and multi-lobed in some species), lungs (present only in air-breathers), kidneys, bladder, sex organs. Veins: the great blood vessels (aorta and vena cava) described in remarkable anatomical detail, with extensive comparative data across dozens of species.
Book III: Veins, muscles, semen
1–22 509b26–521b5
Veins, bones, muscles, brain, and semen
The vascular system in detail: Aristotle traces the principal veins from the heart outward through the body, comparing human anatomy with that of other vertebrates. Bones and cartilage (harder in males, in older animals, in land animals); muscles and sinews (tendons and ligaments — their distribution and function); fat (around the kidneys, omentum) and suet (in horned animals). Marrow inside bones: its consistency and distribution. Brain: bloodless, cold, and without sensation (Aristotle does not recognize it as the seat of mind — that is the heart). Skin, hair, nails, hooves, horns, feathers. The chapter on semen: its physical nature (thick, white, frothing in fertile males), the organs that produce it, and differences among species.
Book IV: Bloodless animals
1–9 523a31–538a25
Bloodless animals — cephalopods, crustaceans, insects, testacea
The anatomy and natural history of bloodless animals (invertebrates), organized into four classes. Cephalopods (malakia — 'soft-bodied'): octopus, squid, cuttlefish — described with impressive accuracy (ink sac, chromatophores, beak, tentacle suckers). Crustaceans (malakostraka — 'soft-shelled'): crabs, lobsters, shrimp — segmented bodies, claws, molting. Insects (entoma — 'segmented'): bees, wasps, beetles, flies, cicadas, ants — compound eyes, wings, proboscis, stinging apparatus. Testacea (ostrakoderma — 'hard-shelled'): snails, bivalves, sea urchins, ascidians. Includes many correct observations mixed with some errors inherited from fishermen and travelers.
Book V: Reproduction methods
1–33 538b2–558b27
Reproduction methods across the animal kingdom
Comprehensive survey of reproductive methods across the animal kingdom. Sexually reproducing animals: copulation postures and mechanisms in quadrupeds, birds, fish, insects, cephalopods. Mating seasons and breeding cycles. Asexual generation: budding in sponges, fragmentation in worms, spontaneous generation in insects (from dew, mud, dung, rotting matter — a universal ancient error). Details of insect metamorphosis (grubs → pupae → adults) observed with considerable care. Breeding habits of specific species: horses, cattle, elephants, dolphins, various fish. Duration of gestation in different mammals. Oviparity vs. viviparity vs. ovoviviparity (some sharks give live birth after internal development of eggs).
Book VI: Birds and oviparous animals
1–37 558b28–580a22
Bird eggs, chick development, and oviparous fish
Reproduction in egg-laying animals. Bird eggs: their formation within the female (yolk forms first, then white, then shell), the process of fertilization, incubation temperatures and times, development of the chick embryo day by day (among the most impressive observational passages in ancient science). Wind eggs (unfertilized eggs laid by isolated hens). Oviparous fish: spawning behavior, external fertilization, development of eggs. Vipers and sharks: exceptional ovoviviparity described accurately. Seasonal patterns: when different species breed, how long eggs take to hatch, care of young. Many specific observations about particular bird species — hawks, cuckoos, swallows, herons, pelicans, eagles.
Book VII: Human reproduction
1–12 580a23–588a18
Human puberty, pregnancy, and childbirth
Human sexual development and reproduction. Puberty: physical changes in males (voice, body hair, semen production — around age 14) and females (breast development, menstruation — around age 12–14). Menstruation: frequency, duration, relationship to fertility. Conception: signs of successful conception, sex determination (Aristotle's account involves relative heat of parents' contributions). Pregnancy: development of the embryo, quickening, cravings, physical changes in the mother. Duration of gestation (7 months is the minimum for viability; 10 months is possible). Childbirth: presentation, difficulties, multiple births (twins). Lactation and early infancy. Some scholars consider this book a later compilation, but the material is consistent with Aristotelian biology.
Book VIII: Animal behavior and ecology
1–30 588a18–607b2
Diet, habitat, migration, hibernation, diseases
A remarkable zoological ethology — animal behavior in relation to environment. Diet: what each species eats and how (herbivores, carnivores, omnivores; filter-feeders, predators, scavengers). Habitat: marine, freshwater, terrestrial, amphibious. Migration: birds (cranes flying south), fish (tuna moving between open sea and coastal waters). Hibernation: bears, dormice, swallows (Aristotle incorrectly includes them), snakes. Seasonal changes in behavior and appearance. Diseases of animals: rabies in dogs, infections in sheep, parasites in fish. Responses to weather: animals sensing earthquakes, storms, changes of season. Practical knowledge drawn from farmers, fishermen, beekeepers, and Aristotle's own observations on Lesbos.
Book IX: Character and intelligence
1–51 608a11–631b5
Animal character, intelligence, and social insects
Animal 'character' (ēthos) and intelligence — the most anecdotal and anthropomorphic book. Some animals are gentle (sheep, deer), others fierce (boar, bear); some cunning (fox, octopus), others simple. Rivalries and friendships between species (eagles and snakes are enemies; plovers and crocodiles cooperate). Extensive treatment of social insects: the bee colony (queen, workers, drones — their division of labor, wax-building, honey-production, swarming), ant colonies (organization, food storage, coordinated foraging), spider web-construction. Intelligence in dolphins, elephants, and primates. Animal tool use and problem-solving. The book's authorship is sometimes questioned — it contains more hearsay and traveler's tales than Aristotle's usual standard — but it remains a foundational text of comparative ethology.
Book X: Causes of barrenness
1–7 633b8–638b38
Causes of barrenness in humans and animals
Infertility and its causes — in both humans and animals. Male causes: deficiency in semen quantity or quality, physical malformations, excessive heat or cold destroying fertility. Female causes: malformation of uterus, dryness preventing conception, excessive fat obstructing passages. Environmental factors: diet, age, timing of intercourse. Treatments and signs of fertility. This book is widely regarded as a later addition — possibly by a Peripatetic successor rather than Aristotle himself — based on its abrupt style, overlap with Generation of Animals, and placement at the end of the work.
Parts of Animals
Investigates why animals have the parts they do, explaining bodily structures through final causation. The most philosophical of the biological treatises.
Book I: Method
1–5 639a1–646a3
Method — final causes and the study of humble creatures
The methodological preface to Aristotle's explanatory biology — often considered his most important statement on scientific method after the Posterior Analytics. The natural scientist must explain through final causes: we do not say teeth are hard and sharp because they grew that way (material/efficient cause), but that they grew that way in order to cut (final cause). Division into genera must proceed by multiple differentiae, not by dichotomy alone. The famous passage defending the study of humble creatures: 'We should venture on the study of every kind of animal without distaste; for each and all will reveal to us something natural and something beautiful.' Absence of haphazard and conduciveness of everything to an end are found in nature's works in the highest degree, and the resultant end of her generations and combinations is a form of the beautiful.
Book II: Homogeneous parts
1–9 646a8–661b27
Blood, fat, brain, bone, and other uniform tissues
Homogeneous parts (uniform tissues): blood, fat, suet, marrow, brain, flesh, bone, cartilage, sinew, skin, membrane, hair, nails. Blood is the ultimate nourishment of the body — it is the material from which all other parts are formed. Hot, thin blood produces courage and intelligence; cold, thick blood produces heaviness and stupidity. Fat (in bloodless animals, the analogue): its distribution and purpose (reserve nourishment, insulation). Brain: cold and bloodless, it counterbalances the heat of the heart and prevents overheating. Bone provides structural support; cartilage provides flexible support in ears, nose, windpipe. Each tissue is explained by its function in the organism — final causation applied systematically.
Book III: Non-homogeneous parts I
1–14 661b28–678b29
Heart, lungs, liver, kidneys — organs of the trunk
Non-homogeneous (instrumental) parts of the trunk: organs composed of different tissues arranged for specific functions. The heart: seat of the soul, center of the vascular system, source of vital heat — present in all blooded animals, first organ to form in the embryo, last to cease functioning at death. Lungs: for cooling the blood (large lungs → large body → more heat to cool). Liver: concocts blood from food. Spleen: subsidiary to the liver. Kidneys: filter waste from the blood. Bladder: stores liquid waste. Gall bladder: separates bile from the blood (not present in all species — its absence correlates with longevity and temperament). Each organ explained teleologically: its material composition serves its function, which serves the good of the whole animal.
Book IV: Non-homogeneous parts II
1–14 678b30–697b30
Head, limbs, horns, and compensatory economy
Non-homogeneous parts of the head, extremities, and body surface. Mouth and teeth: adapted to diet (sharp teeth for carnivores, flat molars for herbivores, tusks for defense). Tongue: for taste in all, for speech in humans alone. Lips, nose, ears — each adapted to its function and varying with species. Eyes: their color, number of lids, and placement (forward in predators for depth perception, lateral in prey for wide vision). Horns, antlers, tusks: defensive weapons whose material is redirected from other potential structures (horned animals generally lack upper teeth). Limbs: number and arrangement adapted to locomotion type. Tail: variable — for fly-swatting, balance, or display. Throughout, Aristotle applies the principle of 'compensatory economy': nature cannot give generously in every direction at once; what is added in one place is subtracted from another.
On the Movement of Animals
How and why animals move: the need for an external fixed point, the role of the soul, desire, and pneuma in producing locomotion.
Single work
1–5 698a1–701a6
Motion requires a fixed point to push against
Animals cannot move without something external and immovable to push against — just as a man cannot walk on shifting sand without solid ground beneath him. The earth provides this fixed point for terrestrial animals; water and air provide (lesser) resistance for swimmers and flyers. Within the animal's own body, limb-joints function as the internal fixed points: the elbow divides the arm into mover and moved, and the joint itself remains still while the segments on either side move. Aristotle draws an analogy to the cosmos: just as the earth (motionless center) enables all terrestrial motion, the unmoved mover enables cosmic motion. The analysis connects biology, mechanics, and metaphysics through the universal principle that motion requires a fixed reference.
6–11 701a7–704b3
The practical syllogism and connate pneuma
The psycho-physiological mechanism of animal movement. The soul initiates motion through desire (orexis) directed at a perceived or imagined object: the practical syllogism — a universal desire-premise ('I need drink') plus a particular perception ('this is drink') — produces action immediately without further deliberation. The physiological instrument is the connate pneuma (sumphyton pneuma): a hot, airy substance in the region of the heart which, when heated or cooled by desire or aversion, expands or contracts and transmits the soul's impulse to the muscles and limbs. This accounts for involuntary motions (trembling, erection, heartbeat) as well as voluntary locomotion. The heart is the central control: like an automaton's mechanism, it coordinates all bodily movements.
On the Progression of Animals
Why animals have the number of limbs they have, and how body symmetry and limb placement are adapted to the mode of locomotion.
Single work
1–19 704a4–714b23
Why animals have the limbs they have
Why do animals have the number and arrangement of limbs that they do? Aristotle argues from the principle that nature does nothing in vain and always produces the best arrangement compatible with each animal's essence. Bipeds (humans, birds) walk with two legs because their vital heat is greatest and concentrated upward. Quadrupeds need four supports because their heat is less and their body weight is distributed more evenly. Polypods (centipedes, crabs) have many limbs because their bodies are long and low, requiring multiple support points. Limbless animals (snakes, fish) move by undulation: snakes use the ground, fish use water. Why limbs bend in opposite directions (human arms forward, legs backward; horse forelegs backward, hind legs forward) — to maintain balance and enable continuous forward motion. Left-right symmetry ensures stability; the right side is naturally stronger and initiates motion.
Generation of Animals
The most detailed biological work on reproduction: the roles of male and female, the nature of semen and menstrual blood, embryonic development, and heredity.
Book I: Male and female
1–23 715a1–731a30
Male provides form, female provides matter
The roles of male and female in generation. The male provides the formative principle (eidos — form, soul, efficient cause) through semen, which is highly concocted blood containing 'soul-heat' and a generative pneuma. The female provides the material (menstrual blood = matter, the substance to be shaped). Semen does not contribute physical material to the embryo — it contributes the motion and form that organize matter, just as a carpenter's art shapes wood without becoming part of the product. Extensive anatomical survey of reproductive organs across species: testes (internal in birds and fish, external in mammals), uterus (double-horned in some, simple in others), and how they vary with reproductive strategy. The male-female distinction itself is explained: the male can 'concoct' blood to its final product (semen); the female's heat is insufficient for this last step.
Book II: Embryonic development
1–8 731b18–748b7
Heart forms first; viviparity vs. oviparity
How the embryo forms from the interaction of semen and menstrual blood. The semen sets the blood in motion, causing it to coagulate and differentiate — like rennet acting on milk. The heart forms first because it is the source and principle of all other organs. Aristotle distinguishes viviparous animals (bearing live young: most mammals), oviparous (laying eggs: birds, reptiles, fish), and larviparous (producing larvae: most insects). The more 'perfect' the animal, the more developed its young at birth. Discusses at what point the embryo becomes 'alive' and has soul: first nutritive soul alone, then sensitive, finally (in humans) rational. The embryo's nourishment comes through the umbilical cord (in viviparous) or yolk (in oviparous). Aristotle's account is epigenesist — the embryo develops gradually from initially undifferentiated matter, with organs forming sequentially rather than all being present in miniature from the start (preformationism). This position shaped early modern debates about epigenesis, though nineteenth-century embryology moved on to newer experimental and germ-layer frameworks.
Book III: Eggs, bees, spontaneous generation
1–11 748b8–762b18
Chick development, bees, and spontaneous generation
Development within bird eggs described day by day — among Aristotle's finest empirical work. Incubation of the hen's egg: by the fourth day the embryo is visible as a blood-speck; the heart beats; membranes form; yolk and albumen separate into nutritive and protective roles. Fish eggs: external development, the father's role in guarding nests (observed in some species). The generation of bees: a notoriously difficult problem — Aristotle concludes that drones are produced by workers, workers by the 'king' (queen), and kings generate themselves, reflecting his commitment to a male formative principle even where observation is ambiguous. Spontaneous generation (automaton genesis): insects, shellfish, and eels generated from putrefying matter — the surrounding heat and moisture supply what semen would.
Book IV: Heredity and sex
1–8 763b20–788a8
Heredity, sex determination, and monstrosity
Why offspring resemble parents — Aristotle's theory of heredity. Semen contains 'movements' (kinēseis) corresponding to characteristics of both father and paternal ancestors. These movements either dominate the female material (producing resemblance to the father) or fail (producing resemblance to the mother or maternal ancestors). Sex determination: if the male's formative heat fully dominates the female material, the offspring is male; if it fails in this first mastery, the offspring is female. Monstrosity (teras) is an extreme failure: when formative movements go far astray, producing offspring unlike the species — rare and accidental. Superfetation (conceiving while already pregnant), multiple births (twins from separated material), and moles (malformed tissue without proper embryonic development).
Book V: Secondary characteristics
1–8 778a16–789b20
Eye color, hair, skin, voice, and individual variation
Explains secondary physical characteristics that differ among individuals and species. Eye color: related to the amount and type of moisture in the eye (blue = little moisture, dark = much moisture). Hair color and texture: black hair indicates heat (well-concocted), red or blonde indicates less heat; curly hair results from dry exhalation, straight from moist. Skin color: darker skin indicates greater internal heat concocting the surface moisture. Why some animals are born with eyes open and others closed (related to the dryness of the cornea and the stage of development at birth). Teeth: why some are present at birth (horses) and others erupt later (humans). Voice: deep voices from thick air moved by strong heat; high voices from thin, fast-moving air. A comprehensive natural history of individual variation explained through Aristotle's four-element physiology.
Metaphysics
Metaphysics
The capstone of Aristotle's philosophy: the science of being qua being, the study of substance, actuality and potentiality, and the unmoved mover. The fourteen books were assembled by Andronicus.
Book I (Alpha): History of philosophy
1–2 980a21–983a23
All men desire to know; wisdom as knowledge of causes
The famous opening: 'All men by nature desire to know.' The progression from sensation to memory to experience (empeiria) to art (technē) to wisdom (sophia). Wisdom is knowledge of first causes and principles — the most universal, the most difficult, the most exact, and the most authoritative knowledge. The wise person knows the 'why' rather than merely the 'that'. Philosophy begins in wonder (thaumazein) — first at obvious difficulties, then at greater problems like the origins of the universe. It is pursued for its own sake, not for utility, and arose only when leisure permitted speculation beyond necessity.
3–10 983a24–993a27
The first history of philosophy
The first history of philosophy. Aristotle surveys predecessors according to how many and which of the four causes they recognized. The Ionian physicists (Thales, Anaximenes, Heraclitus) grasped only the material cause. Empedocles and Anaxagoras added the efficient cause (Love/Strife; Mind). The Pythagoreans identified form/number as a formal cause. Plato's Theory of Forms attempted to provide formal causes but created more problems than it solved — the 'Third Man' argument, the gap between Forms and sensibles, Forms as non-explanatory of motion. None before Aristotle properly articulated the final cause or distinguished all four causes clearly. The survey demonstrates that Aristotle's own fourfold causal framework is the culmination of the entire philosophical tradition.
Book II (Alpha Minor): On the study of philosophy
1–3 993a30–995a20
Truth is collective; causes cannot regress infinitely
Truth is like a door no one can miss entirely, but no one person grasps the whole. Philosophy is a collective enterprise — we owe gratitude even to those whose views we reject, for they exercised the habit of thought we inherit. There cannot be an infinite regress of causes: in each type of cause — material, formal, efficient, final — the series must terminate. Otherwise nothing would be explained, and knowledge would be impossible. The chapter on method: we should not demand the same precision in every field — mathematical exactness is inappropriate for rhetoric, and persuasive plausibility insufficient for mathematics. Each science has its appropriate standard of rigor.
Book III (Beta): Philosophical puzzles
1–6 995a24–1003a5
Fourteen aporiai for first philosophy
Fourteen aporiai (philosophical puzzles or impasses) that first philosophy must resolve. Among them: Does a single science study all four causes, or do different sciences treat different causes? Does the science of being also study the axioms (like non-contradiction)? Are the principles of perishable and imperishable things the same? Are genera or ultimate constituents the principles of things? Do Forms exist? Are mathematical objects intermediate between Forms and sensibles? Are principles universal or individual? Are they actual or potential? The method of setting out aporiai before attempting solutions is distinctive: by wrestling with genuine difficulties on both sides, we avoid facile answers and ensure that our eventual solutions truly resolve the underlying problems.
Book IV (Gamma): Being and first principles
1–2 1003a21–1005a18
Being qua being; substance as focal meaning
There is a science of being qua being (on hēi on) — it studies what belongs to being as such, unlike the special sciences which carve off a particular region of being. Being is said in many ways (pollachōs legetai), but all these ways are unified by reference to one central meaning: substance (ousia). Health, medical, healthy all relate to one thing — health. Similarly 'being' in the categories of quality, quantity, relation, etc. all relate to substance. This 'focal meaning' (pros hen) structure explains how a single science can study what is said in many ways without collapsing into mere homonymy. First philosophy studies substance primarily, and the other categories derivatively.
3–8 1005a19–1012b31
Defense of the Principle of Non-Contradiction
Defense of the Principle of Non-Contradiction (PNC) — the firmest of all principles. It cannot be demonstrated (for all demonstration presupposes it), but anyone who denies it can be refuted 'elenctically': the moment they say anything meaningful, they must signify one definite thing rather than its contradictory, and thereby they already presuppose PNC. Detailed refutation of Protagorean relativism ('man is the measure of all things'): if every appearance were true, contradictories would be simultaneously true, all things would be one, and thought would be impossible. The sources of relativism are diagnosed: confusion of being with appearing, observation that contraries arise from the same thing, and the Heraclitean doctrine of universal flux.
Book V (Delta): Philosophical lexicon
1–30 1012b34–1025a34
Philosophical lexicon — thirty key terms defined
A philosophical dictionary defining thirty key terms in their various senses: principle (archē — six senses), cause (aition — the four causes), element (stoicheion), nature (phusis — form vs. matter), necessary (anankaion), one (hen — continuous, whole, individual, universal), being (on — essential/in-itself, accidental, true/false, potential/actual), substance (ousia — the ultimate subject), same/other, prior/posterior, potentiality (dunamis), quantity (poson), quality (poion), relation (pros ti), complete (teleion), limit (peras), 'in virtue of which', disposition, having, privation, part, whole, genus, false, accident. Each entry distinguishes multiple meanings, often identifying which sense is primary. This book is not argumentative but definitional — an indispensable reference for the rest of the Metaphysics and for Aristotelian philosophy generally.
Book VI (Epsilon): Being and truth
1–4 1025b3–1028a6
First philosophy as theology; accidental being excluded
First philosophy (theology/metaphysics) studies being qua being and the immovable causes. It differs from physics (which studies movable substances) and mathematics (which studies immovable but non-separate objects). If there were no immovable separate substance, physics would be first philosophy — but there is such a substance, and the science of it is universal precisely because it is primary. Two kinds of being that first philosophy does NOT study as its primary subject: accidental being (what happens by chance, e.g., 'the musician builds') and being-as-truth (merely the mind's combining/separating in judgment, not a feature of things in themselves). The proper subject is being in the primary categories — above all, substance.
Book VII (Zeta): What is substance?
1–6 1028a10–1032a11
Substance is primary; four candidates examined
The central book of the Metaphysics — often called the most difficult sustained argument in ancient philosophy. Substance (ousia) is the primary category of being: all other categories (quality, quantity, etc.) depend on substance. Four candidates for 'substance': (1) the essence (to ti ēn einai), (2) the universal, (3) the genus, (4) the subject/substratum. The substratum criterion alone is insufficient — it leads to bare matter, which is not 'this something' (tode ti). Essence is the 'what it was to be' for a thing: the formula (logos) expressing what something is in virtue of itself, not incidentally. Only substances in the primary sense have essences strictly speaking.
7–9 1032a12–1034b19
Coming-to-be — form does not come-to-be
Coming-to-be and substance. Everything generated is generated from something (matter), by something (an efficient cause possessing the form), and into something (the form). The form itself does not come-to-be — what comes-to-be is the composite of form and matter. A man begets a man: the form pre-exists in the father and is transmitted to the matter provided by the mother. Art imitates nature in this: the doctor's art (possessing the form of health) produces health in the patient's body. This has crucial implications: Forms are not generated, so there is no regress of Forms being generated by prior Forms.
10–17 1034b20–1041b33
Universals are not substances; form as organizing cause
Is the formula (definition) of the whole identical to the sum of the formulae of the parts? The answer depends on whether we are defining the form alone or the composite. The form's formula does not include matter; the composite's does. Universals are not substances: what is common to many cannot be the essence of any one of them (the 'universal is not substance' thesis, directed against Platonism). The culmination (ch. 17): substance is not an element or component but a principle and cause — specifically the cause of matter's being organized as a unity. What makes flesh and bones into a human being? The form/soul. Substance is thus primarily form, understood as an organizing principle — though the precise meaning of this claim (whether Aristotle means individual forms, universal forms, or form as causal principle) remains among the most contested questions in all of Aristotle scholarship.
Book VIII (Eta): Matter and substance
1–6 1042a3–1045b23
Matter, form, and the unity of definition
Recapitulates and extends Zeta. Sensible substances have matter that underlies change. Form is the differentia that makes matter into a definite kind of thing — as 'threshold' differentiates wood into a door-component. The unity of definition (why 'two-footed animal' is one thing, not a mere conjunction) is explained by the actuality/potentiality distinction: the genus is matter (potential), the differentia is form (actual), and matter-informed-by-form is intrinsically one — not needing any external unifier. This is Aristotle's elegant solution to the ancient 'problem of the one and the many' as applied to definition: the genus and differentia are related as potentiality and actuality, which are not two things but one thing in different descriptions.
Book IX (Theta): Potentiality and actuality
1–5 1045b27–1048a24
Potentiality — rational vs. irrational capacities
Potentiality (dunamis) in the primary sense: the capacity for change in another thing or in the same thing qua other. Rational potentialities (art, knowledge) differ from irrational ones: a rational potentiality can produce opposites (medicine can heal or harm), while an irrational potentiality produces only one outcome (fire can only heat). For a rational potentiality to be actualized, desire or choice must determine which opposite is realized. Conditions of actualization: the agent must be present, the patient must be suitably disposed, and nothing external must prevent the interaction. The Megarian objection (that potentiality exists only when actuality exists) is refuted: it would make change unintelligible.
6–10 1048a25–1052a11
Actuality is prior in definition, time, and substance
Actuality (energeia/entelechia) is prior to potentiality in three ways: (1) in definition — we define the potential by reference to the actuality it is a potential for; (2) in time — though the individual potential thing exists before its actualization, the actuality of the species is always prior (a man begets a man); (3) in substance — actuality is the end (telos) for the sake of which the potentiality exists, and the end is ontologically more fundamental than what is for its sake. Eternal things are fully actual and have no unrealized potentiality. Chapter 10 extends actuality to truth: being-as-truth is the mind's contact with the simple and incomposite — a direct 'touching' (thigein) that cannot be false, only achieved or not achieved.
Book X (Iota): Unity and opposition
1–10 1052a15–1059a14
Unity, measure, opposition, and contrariety
Unity (to hen): 'one' is said in many ways — continuous, whole, individual, universal. But the primary sense is 'one' as measure (metron): in each category, the one is the unit of measurement. In numbers, the unit; in music, the quarter-tone; in length, the foot. Being and one are convertible (every being is one, and every one is a being) but they are not a single substance underlying things (against the Pythagoreans and Platonists). Opposition: four types — contradiction, contrariety, privation/possession, relation. Contrariety is the most complete opposition within a genus (black and white in color). Intermediates exist between contraries (grey between black and white) but not between contradictories. The perishable and the imperishable differ in genus, not merely in species — a fundamental principle for the separation of physics from theology.
Book XI (Kappa): Summary
1–12 1059a18–1069a14
Summary of Books III–VI and Physics III–V
An abbreviated recapitulation of Books III–VI of the Metaphysics and Physics III–V. Its status is debated: it is often treated as an alternative draft, epitome, or student compilation rather than a polished Aristotelian text. It covers: the aporiai of Book III, being qua being and the PNC (from IV), the definitions of key terms (from V–VI), the classification of sciences, infinity, motion, and change (from Physics). Its value lies in occasionally providing clearer or simpler formulations of complex arguments, and in confirming that the doctrines of the other books were understood in their essentials by the early Peripatetic school.
Book XII (Lambda): The divine intellect
1–5 1069a18–1071b22
Three kinds of substance; eternal motion needs eternal cause
Three kinds of substance: (1) sensible perishable (plants, animals — studied by physics), (2) sensible eternal (celestial bodies — studied by astronomy), (3) immovable and eternal (the object of theology/first philosophy). All sensible substances have matter and are subject to change; they require both a form and a substratum. The four types of change (substance, quality, quantity, place) all require something actual that produces the change and something potential that receives it. Eternal motion requires an eternally actual mover — otherwise the cosmos could in principle cease to operate. Potentiality alone cannot explain the existence of an eternal cosmos: if everything were merely potential, nothing would ever have come to be.
6–10 1071b3–1076a4
The Unmoved Mover — thought thinking itself
The Unmoved Mover: there must exist a substance that is pure actuality (energeia) with no potentiality — otherwise it could fail to cause motion, and the heavens could stop. This substance moves the outermost celestial sphere as an object of desire and love (hōs erōmenon) — it is the final cause of cosmic motion, not an efficient cause pushing from behind. Its activity is thinking (noēsis): the best and most divine activity. What does it think? Only what is most excellent — itself. It is 'thought thinking itself' (noēsis noēseōs noēsis) — self-contemplating intellect, fully actual, completely unified, eternal, and perfect. This is Aristotle's God: not a creator, not provident over human affairs, but the eternal self-thinking thought that is the final cause of all cosmic motion and the paradigm of the highest life. Later interpreters tried to systematize the celestial motions into 47 or 55 movers, but Aristotle himself does not settle the exact count here, leaving the relationship between the many movers and the single supreme mover unresolved.
Books XIII–XIV (Mu–Nu): Forms and mathematicals
XIII–XIV 1076a8–1093b29
Critique of Platonic Forms and mathematical objects
Extended critique of Platonic metaphysics: the Theory of Forms and the Academic theories of mathematical objects. Book XIII: mathematical objects (numbers, lines, planes) are not separate substances existing independently of sensible things — they are arrived at by abstraction (aphairesis) from sensible things and exist 'in' them, not apart. The Forms are subject to devastating criticism: the 'Third Man' regress, the inability of unchanging Forms to explain change, the duplication problem (a separate world that merely mirrors this one). Book XIV: attacks the Platonic identification of principles with numbers and the 'Great and Small' as material principle. The Indefinite Dyad and the One cannot generate numbers or explain plurality. These books represent Aristotle's most sustained polemic against his own philosophical education in the Academy.
Ethics
Nicomachean Ethics
The most important work in ancient ethics. Aristotle examines happiness (eudaimonia), virtue, practical wisdom, friendship, and the good life — culminating in contemplative activity.
Book I: The good and happiness
1–3 1094a1–1095b13
The highest good and the master science of politics
Every art, inquiry, action, and pursuit aims at some good — hence the good is 'that at which all things aim.' But goods form a hierarchy: lower goods (bridle-making) are subordinate to higher goods (horsemanship) which are subordinate to a master science (politics — which orders all activities toward the good of the city). Ethics is a branch of political science. Methodology: we must be content with 'the outline of truth' since the subject matter (human action) admits of variation. The young are not suitable students of ethics: they lack experience and are led by their passions. We seek not to know what virtue is but to become virtuous.
4–8 1095a14–1099a7
The function argument — happiness as rational activity
What is happiness (eudaimonia)? Everyone agrees happiness is the highest good, but they disagree about its content. Three candidate lives: pleasure (the life of enjoyment — slavish), honor (the political life — too dependent on others), and contemplation (the philosophical life). Plato's 'Form of the Good' is examined and rejected: a universal, separate Good is useless for action. Aristotle's positive account: the function argument (ergon). If every craftsman, organ, and species has a function (proper work), humans must too. The human function is rational activity — activity of the soul in accordance with virtue (aretē), and if there are several virtues, in accordance with the best and most complete virtue, in a complete life. Happiness is thus the excellent exercise of distinctively human capacities over a whole lifetime — 'one swallow does not make a summer, nor does one day; and so too one day, or a short time, does not make a man blessed and happy' (1098a18).
9–13 1099a7–1102a38
External goods, fortune, and the soul's division
External goods: happiness requires some external equipment — wealth, friends, good birth, good children, beauty. Their absence mars blessedness. Yet virtue is the controlling factor: no truly virtuous person is ever completely miserable, even in misfortune (the test of nobility under suffering). The soul and its division: the irrational part (vegetative — not amenable to reason; and appetitive — amenable to reason in the sense that it can obey and be trained) and the rational part (which issues commands). Moral virtue (ethikē aretē) perfects the appetitive part in its obedience to reason; intellectual virtue (dianoetikē) perfects the rational part directly. This division structures the rest of the treatise.
Book II: Moral virtue
1–4 1103a14–1105b18
Virtue acquired by habituation, not by nature
Moral virtues are acquired by habituation (ethos → ethikē aretē), not by nature. We become just by doing just acts, brave by doing brave acts — just as we become builders by building. Nature gives us the capacity for virtue; habit actualizes it. The legislator's task is to make citizens good through habituation. Virtue is about pleasures and pains: we must be trained to take pleasure in the right things and feel pain at the wrong things. Signs that a hexis (stable disposition) has been acquired: we do virtuous acts with pleasure, not reluctantly. Three conditions for a genuinely virtuous act: (1) the agent knows what they are doing; (2) they choose it for its own sake; (3) they act from a firm and stable character.
5–9 1105b19–1109b26
The doctrine of the mean
Virtue is a hexis (stable disposition), not a pathos (emotion) or a dunamis (mere capacity). It is a hexis of choosing (hexis prohairetikē) that lies in a mean (mesotēs) relative to us, as determined by reason — specifically as the person of practical wisdom (phronimos) would determine it. The mean is between two vices: excess and deficiency. Courage is the mean between cowardice (deficiency) and rashness (excess); temperance between insensibility and self-indulgence. The mean is not arithmetic but relative to the individual and circumstance — what is moderate food for an Olympic wrestler is excessive for a beginner. Some actions admit no mean: murder, theft, adultery are intrinsically wrong. Practical advice for hitting the mean: aim at the lesser evil, beware the pleasant, correct for personal bias.
Book III: Voluntariness and particular virtues
1–5 1109b30–1115a3
Voluntary action, choice, and deliberation
Voluntary (hekousion) vs. involuntary (akousion) action — essential because praise, blame, and responsibility depend on this distinction. Actions done under compulsion (force from outside, no contribution from the agent) or in ignorance (of the particular circumstances, not of universal moral principles) are involuntary. 'Mixed' actions (done under threat, e.g., throwing cargo overboard in a storm) are voluntary but done with regret — they are chosen in the circumstances. Choice (prohairesis): not a wish, not an appetite, not an opinion. It is the deliberate desire for what is in our power, arrived at through deliberation. Deliberation (bouleusis): about means to ends, not about ends themselves. We deliberate about what is in our power and not fixed by nature.
6–12 1115a4–1119b18
Courage and temperance
The first two particular virtues. Courage (andreia): the mean between cowardice and rashness regarding things that inspire fear — specifically, a noble death in battle. Five imperfect forms of courage distinguished from true courage: civic courage (from shame or legal penalty), experience-based confidence, spiritedness (thumos), optimism, and ignorance of danger. True courage acts for the sake of the noble (to kalon), knowingly facing danger. Temperance (sōphrosunē): the mean regarding bodily pleasures — specifically touch and taste (not sight or hearing). The intemperate person desires excessive pleasures; the temperate person desires moderate pleasures and takes them moderately. Intemperance is more voluntary than cowardice, and hence more blameworthy.
Book IV: The social virtues
1–9 1119b22–1128b35
Generosity, magnificence, and magnanimity
Generosity (eleutheriotes): the mean regarding giving and taking of wealth — the generous person gives to the right people, at the right times, with pleasure. Prodigality (excess) and stinginess (deficiency). Magnificence (megaloprepeia): generosity on a grand scale — large and fitting expenditure for public goods (festivals, warships, temples). The magnificent person spends greatly and tastefully; the vulgar person spends greatly without taste; the niggardly person falls short. Magnanimity (megalopsuchia — 'greatness of soul'): perhaps the most distinctively Aristotelian virtue. The magnanimous person knows themselves to be worthy of great things and is worthy — they are concerned with honor but not overly so, they speak their mind, move slowly, have a deep voice, and are self-sufficient. Proper ambition: the unnamed mean regarding honor on a smaller scale.
6–9 1126b11–1128b35
Truthfulness, wit, and friendliness
Three social virtues governing everyday interactions. Truthfulness (alētheia): the truthful person neither exaggerates (the boaster — alazōn) nor understates (the self-deprecating person — eirōn, the 'ironist'). Wit (eutrapelia): the tactful person jokes appropriately, neither buffoonishly nor humorlessly. Friendliness (philia in its social sense): the friendly person is pleasant in company without flattery or quarrelsomeness. These virtues concern not great occasions but the texture of daily life — the character traits that make a person agreeable and honest in ordinary social exchange.
Book V: Justice
1–5 1129a3–1133b28
General and particular justice; distributive proportion
Justice (dikaiosunē) in two senses. General (complete) justice: the whole of virtue exercised toward others — the lawful person who acts virtuously in their dealings with fellow citizens. 'Justice in this sense is not a part of virtue but the whole of virtue; injustice not a part of vice but the whole of vice.' Particular justice: a specific virtue concerned with fair distribution and fair exchange. Distributive justice (en tais dianomais): distribution of honors, wealth, and offices according to some proportion — geometric proportionality (equals treated equally, unequals treated proportionally to their relevant differences). What counts as the relevant criterion depends on the constitution: democracy uses free birth, oligarchy wealth, aristocracy virtue.
6–11 1134a1–1138b13
Corrective justice, equity, and natural vs. conventional
Corrective (rectificatory) justice: restores equality after a wrong — it uses arithmetic proportion, treating both parties as equals before the law regardless of character. The voluntary/involuntary distinction in unjust acts: injury from ignorance is a misadventure; injury from non-deliberate passion is unjust but not necessarily evidence of an unjust character; injury from deliberate choice reveals a truly unjust person. Equity (epieikeia): a corrective to strict legal justice — the equitable person goes beyond the letter of the law to capture its spirit in particular cases that the legislator did not foresee. 'The equitable is just, and better than one kind of justice — not better than absolute justice but better than the error that arises from the absoluteness of the statement... a correction of law where it is defective owing to its universality.' Natural vs. conventional justice: some things are just everywhere (natural justice); others are just only because a community has agreed on them (conventional).
Book VI: Intellectual virtues
1–8 1138b18–1142a30
Five intellectual virtues — including phronēsis and sophia
The rational soul has two parts: the scientific (epistēmonikon — grasps necessary truths) and the calculative/deliberative (logistikon — grasps contingent things that can be otherwise). Five intellectual virtues, each being the best hexis of its respective cognitive capacity: (1) Epistēmē (scientific knowledge): knowledge of the necessary and eternal, through demonstration. (2) Technē (art/craft): productive knowledge — knowing how to make things, with a true rational account. (3) Phronēsis (practical wisdom): the capacity to deliberate well about what is good and advantageous for oneself and for human life generally — concerned with action, not production. (4) Nous (intellect/intuition): the faculty that grasps first principles directly, without demonstration. (5) Sophia (theoretical wisdom): the combination of nous and epistēmē — knowledge of the highest things (divine, eternal, necessary).
9–13 1142a31–1145a11
Practical wisdom unites intellect and moral virtue
Practical wisdom (phronēsis) examined in depth. It is concerned with particulars as well as universals — one must perceive the specific situation correctly. Good deliberation (euboulia): correctness of the process of deliberation regarding what promotes the overall good. Understanding (sunesis) and judgment (gnōmē): related faculties for evaluating others' situations. The relationship between phronēsis and moral virtue: you cannot have phronēsis without moral virtue (because vice distorts the perception of ends), and you cannot have genuine moral virtue without phronēsis (because mere 'natural virtue' — a good temperament — without intelligence is blind and can go wrong). Thus phronēsis is the architectonic practical virtue: it makes the other virtues truly virtuous.
Book VII: Continence and pleasure
1–10 1145a15–1152a36
Akrasia — knowing the right but doing the wrong
Continence (enkrateia) and incontinence (akrasia — 'weakness of will'). The incontinent person knows what is right but acts against this knowledge under the pressure of appetite or passion. How is this possible if knowledge determines action? Aristotle's solution: the incontinent person 'has' knowledge only in a qualified sense — like a sleeping or drunk person, they possess it habitually but it is not operative in the moment of action. The practical syllogism: the universal premise ('sweets are bad for me') is possessed but the particular ('this is sweet') triggers appetite before reason can assert itself. Distinction between incontinence regarding appetite (the standard case) and regarding spiritedness (thumos — less blameworthy because spirit listens to reason imperfectly rather than not at all). Brutishness: a level below vice, involving depraved pleasures.
11–14 1152b1–1154b34
First treatment of pleasure as unimpeded activity
First treatment of pleasure (hēdonē). Against the view that pleasure is always bad: some pleasures are bad, but the bodily pleasures of the temperate person and the intellectual pleasures of the wise are genuinely good. Against the view that the good (to agathon) can never be a pleasure: the activity of our best state is most pleasant, so the highest good is accompanied by the highest pleasure. Pleasure is not a process (kinēsis/genesis) toward a natural state (like eating when hungry) but an unimpeded activity (energeia) of a natural state — the pleasure of contemplation is not a filling of a lack but the exercise of a perfected capacity. This positive conception of pleasure anticipates the fuller treatment in Book X.
Book VIII: Friendship (I)
1–8 1155a3–1159a12
Three kinds of friendship — utility, pleasure, virtue
Friendship (philia) is a virtue or implies virtue, and is indispensable for the good life — 'no one would choose to live without friends, even if they had all other goods.' Three kinds of friendship based on three objects of love: (1) utility-friendship (I like you because you are useful to me — typical of business relations), (2) pleasure-friendship (I enjoy your company — typical of youth), (3) virtue-friendship (I love you for your character and wish your good for your own sake). Only virtue-friendship is complete (teleia philia): it is lasting, reciprocal, and rare — it requires time, intimacy, and goodness in both parties. The other two are friendships incidentally — they dissolve when the utility or pleasure ceases.
9–14 1159a12–1163b28
Friendship and political community
Friendship and political community: every form of community (koinōnia) involves a form of friendship and a form of justice. The three correct constitutions — kingship, aristocracy, timocracy (polity) — parallel family relationships (father/child, husband/wife, brothers) and generate corresponding forms of friendship. Their corruptions — tyranny, oligarchy, democracy — have weaker or no friendships (tyranny has the least philia because tyrant and subject have nothing in common). Friendships between unequals (parent/child, ruler/ruled, benefactor/beneficiary): these are proportional — the superior party receives more honor, the inferior more material benefit. Complaints in friendship typically arise from the mismatch between what each party expects.
Book IX: Friendship (II)
1–7 1163b28–1168a27
When to dissolve friendships; benefactors and goodwill
Practical problems of friendship: when to dissolve friendships (when the friend becomes vicious — one owes no continued friendship to a bad person, though one should try to correct them first). The benefactor loves the beneficiary more than vice versa — as the craftsman loves their work more than the work would love the craftsman if it could. Goodwill (eunoia) is a beginning of friendship but not friendship itself (it lacks intimacy and active willing-of-good). Concord (homonoia) in a city — civic friendship — exists when citizens agree on important practical matters and act together on them; it is the political analogue of personal friendship.
8–12 1168a28–1172a15
Self-love, the friend as another self
Self-love (philautia): properly understood, the virtuous person is the truest self-lover because they give themselves the noblest things — noble actions. The vulgar self-lover grasps at pleasure, wealth, and honor for themselves. The good person will sacrifice wealth and even life for friends, since the noble action of sacrifice is worth more to the virtuous agent than what is given up. Does the happy person need friends? Yes: (1) friendship is a virtue and component of happiness; (2) the happy person needs objects of beneficence; (3) life is awareness of one's own goodness, and this awareness is sweetest when shared — 'the friend is another self' (allos autos), and awareness of the friend's existence and goodness is continuous with awareness of one's own.
Book X: Pleasure and the best life
1–5 1172a19–1176a29
Pleasure completes activity as bloom completes youth
Second, more refined treatment of pleasure (superseding VII.11–14). Against Eudoxus's claim that pleasure is the Good (because all things pursue it): true but insufficient — it establishes only that pleasure is a good. Against Speusippus's claim that pleasure is wholly bad: also refuted — it confuses bodily pleasures in excess with pleasure as such. Aristotle's own account: pleasure is not a process but something whole and complete at every instant — like seeing, which is complete at any moment, not like building, which is incomplete until finished. Pleasure 'completes' or 'supervenes upon' activity as a supervenient end — 'as bloom is to youth.' Each activity has its own proper pleasure, and the pleasures of the best activities (intellectual contemplation) are the best pleasures.
6–8 1176a30–1179a32
The contemplative life as highest happiness
The highest happiness: the life of contemplation (theōria). The best activity is the activity of the best faculty (nous) directed at the best objects (the divine, the eternal). Contemplation is the most continuous (we can contemplate longer than we can do anything else), the most pleasant, the most self-sufficient (the contemplator needs only health and basic necessities), the most valued for its own sake (we never ask 'why contemplate?'), and it involves the most leisure. It is the life that most closely approximates the divine life — for God's activity is contemplation, and the extent to which we can share in this activity is the extent of our happiness. The political/practical life is happy in a secondary way: it requires external goods and other people, and its activities are undertaken for ends beyond themselves. Whether Aristotle means that contemplation alone constitutes happiness ('dominant' interpretation) or that the best life includes both contemplation and practical virtue ('inclusive' interpretation) is one of the most debated questions in Aristotle's ethics.
9 1179a33–1181b23
Transition to the Politics — laws and education
Transition to the Politics. Argument alone does not make people good — it is insufficient to move those not already trained by good habituation. Laws are needed to habituate citizens in virtue from youth. Individual fathers cannot do this reliably; the city must take responsibility for education. To legislate well, one must study constitutions — what preserves and what destroys each type. This motivates the Politics: 'Let us then make a fresh start and discuss what sort of constitution is best, how each should be organized, and what laws and customs it should use.' The Nicomachean Ethics thus concludes by embedding individual virtue within the political framework that alone can produce and sustain it.
Eudemian Ethics
An earlier or alternative ethical treatise. Books IV–VI (= NE V–VII) are textually identical and shared between the two works.
Book I: The good
All 1214a1–1220a13
Happiness, self-sufficiency, and the service of god
Opens with a dedication inscription from the temple of Leto at Delos: the good, the beautiful, and the pleasant are separable (unlike the inscription's claim that they coincide). Happiness is the best, most beautiful, and most pleasant thing — but what is it? Reviews popular and philosophical opinions: wealth, honor, health, wisdom, Plato's Form of the Good. Aristotle argues happiness is self-sufficiency plus the exercise of virtue in a complete life. Can happiness be taught, acquired by habituation, or given by fortune? All three contribute, but character-virtue acquired through practice is central. The treatment parallels NE I but with a more theological emphasis — happiness includes the 'service and contemplation of god.'
Book II: Virtue and choice
All 1220a15–1228a17
The mean, voluntariness, and choice as revealing character
Virtue is a state (hexis) productive of good actions and good emotions. It is a mean between excess and deficiency, determined by reason and by what the prudent person would choose. Detailed treatment of voluntariness and choice (prohairesis): choice is deliberate desire (orexis bouleutikē) for things within our power. What we choose reveals character more truly than what we merely do. The voluntary: acting from an internal principle with knowledge of the circumstances. Important differences from NE: the EE's discussion of wish (boulēsis) and its relationship to the good (we wish for what we think good, not for what merely appears good) is more explicit. The EE also gives more attention to the role of fine-feeling (to kalon) as the motive of genuine virtue.
Book III: Particular virtues
All 1228a18–1234b14
Courage, temperance, gentleness, and the fine
Parallel to NE III–IV: individual character virtues examined. Courage: the mean regarding confidence and fear, especially in the face of death in battle. Temperance: the mean regarding bodily pleasures. Gentleness: the mean regarding anger. Generosity and magnificence: regarding wealth. Magnanimity and proper ambition: regarding honor. Some differences from NE: the EE's treatment of courage places more emphasis on the fine (to kalon) as the courageous person's motive, and the discussion of gentleness (praotēs) is fuller. The EE's overall tone is somewhat more austere and intellectualist than the NE — virtuous action is done primarily for its intrinsic beauty rather than from cultivated habit of pleasure.
Books IV–VI (= NE V–VII): Justice, intellectual virtue, continence
All 1129a–1154b (NE numbering)
Shared books on justice, phronēsis, and akrasia
These three books are shared verbatim with the Nicomachean Ethics (= NE V on justice, NE VI on intellectual virtues, NE VII on continence and pleasure). Many scholars believe they were originally composed for the EE and later incorporated into the NE when Andronicus or another editor assembled the corpus — the EE's 'fine' (to kalon) as the motive of virtue and its more theological conception of the good fit better with these books' internal references than does the NE's framework. However, the textual situation remains debated and may never be definitively resolved.
Book VII: Friendship
All 1234b18–1246a25
Three kinds of friendship; the friend as another self
Parallel to NE VIII–IX but more concise. Friendship (philia) is either a virtue or involves virtue. Three kinds: friendship based on utility, pleasure, and virtue/character. Only the last is complete friendship — it includes the other two as consequences. The friend as 'another self' (allos autos): we perceive the friend's existence and goodness as an extension of our own self-awareness. Discussion of friendship with oneself (the good person is unified and consistent, hence self-concordant; the bad person is at war with themselves). Political friendship and justice are treated as macro-versions of personal friendship. The EE's treatment is notable for its greater attention to equality in friendship and to the question of whether the happy person is self-sufficient without friends.
Book VIII: Divine fortune
All 1246a26–1249b25
Good fortune, kalokagathia, and contemplation of god
The most distinctive section of the EE — with no parallel in the NE. On good fortune (eutuchia): some people seem consistently lucky without virtue or prudence. Is this a natural gift, a divine dispensation, or mere chance? Aristotle entertains the idea of a natural irrational impulse (hormē) that consistently aims well — analogous to the enthusiast who 'sees' correctly without reasoning. The concept of kalokagathia (nobility-and-goodness): the complete human excellence combining all virtues with external goods and using them for the sake of the fine. The ultimate human good is 'whatever choice and possession of natural goods — whether bodily goods, wealth, friends, or other things — will most produce the contemplation of god.' This theological conclusion distinguishes the EE from the NE's more autonomous eudaimonism.
Magna Moralia
A third ethical treatise covering happiness, virtue, choice, friendship, and the good life. Authorship is contested, and many scholars treat it as a later Peripatetic epitome or compilation rather than a work by Aristotle himself.
Disputed authorshipAuthenticity disputed. Often treated as a later Peripatetic compilation or epitome drawing heavily on Aristotelian ethics, rather than as a secure work by Aristotle himself.
Book I: Goods and virtues
All 1181a24–1197b20
The good, the mean, and individual virtues simplified
Reviews predecessors on the good (Pythagoras, Socrates, Plato) and critiques the Form of the Good. Happiness is defined as the best good attainable by action in accordance with complete virtue. The soul is divided into rational and irrational (appetitive) parts. Moral virtue is treated as a mean between excess and deficiency — in a more compressed and schematic way than in either the Nicomachean or Eudemian Ethics. Individual virtues, voluntary action, choice, and deliberation are presented in broadly Aristotelian terms, but the treatise is usually read as an abridging or school-level presentation rather than as a secure statement of Aristotle's own wording or structure.
Book II: Justice, friendship, the good life
All 1197b21–1213b30
Justice, continence, friendship, and kalokagathia
Treats justice, equity, practical wisdom, continence and incontinence, friendship, self-love, and the role of fortune in happiness. Much of the material parallels recognizably Aristotelian ethical doctrine, including the three kinds of friendship and the distinction between distributive and corrective justice. The work concludes with kalokagathia — nobility-and-goodness — as a picture of complete ethical excellence. It is best used as evidence for the later transmission and simplification of Aristotelian practical philosophy, not as an unproblematic third ethics treatise by Aristotle.
Politics
Politics
Aristotle's political science: humans are political animals by nature. Examines the household, the city-state, types of constitutions, their corruptions, revolution, and the ideal state.
Book I: Household and city
1–2 1252a1–1253a38
Man is by nature a political animal
The city (polis) is the most sovereign community, encompassing all others and aiming at the highest good. It arises naturally from the development of more primitive associations: male-female (for reproduction), master-slave (for daily maintenance), household (oikos — combining both), village (several households), and finally the city-state (self-sufficient for the good life). The city is 'prior by nature' to the individual — as the whole body is prior to its parts — because only within a city can humans achieve their full nature. 'Man is by nature a political animal' (zōon politikon): the possession of speech (logos) distinguishes humans from animals that merely have voice (phōnē). Speech enables the communication of the just and unjust, the good and bad — and it is the sharing of these judgments that constitutes a household and a city.
3–13 1253b1–1260b24
Household, natural slavery, and the art of acquisition
The household: its three relations — master/slave, husband/wife, parent/child — plus the art of acquisition (chrēmatistikē). Aristotle argues that some humans are 'slaves by nature': in his view, they possess enough reason to apprehend rational guidance but not enough to deliberate independently, and so supposedly benefit from a master's rule. He also concedes that conventional slavery by conquest often enslaves people who are not natural slaves, exposing a tension in the doctrine itself. The argument is now read less as a defensible anthropology than as a historically influential rationalization of Greek social hierarchy. Acquisition: the 'natural' art of acquisition provides what the household needs from nature (farming, herding, hunting); unnatural chrēmatistics (retail trade, money-lending) pursues unlimited profit and is condemned as contrary to nature.
Book II: Critique of ideal states
1–6 1260b27–1269a28
Critiques of Plato's Republic and Laws
Critical examination of proposed ideal constitutions. Plato's Republic: communism of wives, children, and property would not produce the unity Plato desires but would dissolve the bonds of affection — 'what is common to the most people receives the least care' (1261b33), one of the most quoted arguments in all of political philosophy against communal ownership. Private property with generous use is better: it preserves the pleasure of calling something 'one's own' while sharing benefits. The communism of the Laws is also critiqued but more mildly. Phaleas of Chalcedon: proposed equalizing property but neglected desires (which are unlimited) and failed to equalize education. Hippodamus of Miletus: divided citizens into three classes, land into three portions, and laws into three types — criticized for over-schematization and impractical details.
7–12 1271b20–1274b28
Sparta, Crete, Carthage, and Solon evaluated
Examination of actual admired constitutions. Sparta: praised for its education and mixed constitution, but criticized for its treatment of women (who are undisciplined and own too much property), its corrupt kingship, its defective system of communal meals, and its exclusive orientation toward military virtue rather than full virtue. Crete: similar to Sparta but earlier; Aristotle treats its dependent labor system and communal institutions as less unstable than Sparta's because they are integrated into the island's city-structure rather than provoking the same kind of internal revolt. Carthage: praised as well-governed (a mix of aristocracy and democracy), but deviates toward oligarchy in allowing offices to be purchased. Solon of Athens: praised for establishing the mixed constitution that combined democratic and oligarchic elements. Throughout, Aristotle evaluates constitutions by whether they aim at common good and produce stable, virtuous communities.
Book III: Citizenship and constitutions
1–5 1274b32–1278b5
Who is a citizen? Participation in office
Who is a citizen (politēs)? The citizen is defined by participation: the right to share in deliberative and judicial office. Mere residence does not make one a citizen (metics and slaves reside but are not citizens). The virtue of a good citizen is relative to the constitution: a citizen in a democracy needs different capacities than one in an aristocracy. But the virtue of a good human being is absolute. Only in the best constitution do the virtue of the good citizen and the good person coincide — where the rulers possess complete human virtue. Laborers, craftsmen, and merchants lack the leisure for virtue and are not citizens in the best state (a controversial claim reflecting Greek aristocratic assumptions).
6–13 1278b6–1284b34
Six constitutions — three correct, three deviant
Classification of constitutions. A constitution (politeia) is an arrangement of offices determining who rules. Constitutions divide by (a) number of rulers — one, few, many — and (b) whether they rule for the common good or their own interest. Correct forms: kingship (one ruling for the common good), aristocracy (few — the best — ruling for the common good), polity/timocracy (the many ruling for the common good). Deviant forms: tyranny (perverted kingship — rule of one for personal gain), oligarchy (perverted aristocracy — rule of the wealthy for their benefit), democracy (perverted polity — rule of the poor for their benefit). The real distinction between oligarchy and democracy is not number but class: oligarchy is the rule of the rich, democracy of the poor. Justice is disputed: democrats say equal free birth merits equal rights; oligarchs say unequal wealth merits unequal rights.
14–18 1284b35–1288b6
Five kinds of kingship; rule of law vs. rule of persons
Five forms of kingship examined: the Spartan generalship, the barbarian hereditary kingship, the elected dictatorship (aisymnēteia), the heroic-age kingship, and absolute kingship (pambasileia). Should the best person rule, or the best law? Law is reason without appetite (nous aneu orexeōs); a human ruler brings judgment that law cannot provide for particular cases. If one person is outstanding in virtue beyond all others (like a god among humans), absolute kingship is justified — such a person is 'law unto himself.' But such persons are rare or non-existent; in most circumstances, the rule of law combined with office-holders is preferable. The argument for collective wisdom: the many, though individually mediocre, may collectively surpass the few wise (as a feast to which all contribute exceeds a single person's dinner).
Book IV: Real constitutions
1–10 1288b10–1295a24
Species of democracy and oligarchy; the middle constitution
Political science must study not only the ideal constitution but also what is best given particular circumstances, what most cities can realistically achieve, and how existing constitutions can be preserved. Multiple species of democracy (from moderate to extreme): they differ according to which class predominates and how much authority the assembly and courts have. Multiple species of oligarchy: from broad (many wealthy sharing power) to narrow (a closed dynastic clique). The middle constitution (polity/mesē politeia): blends oligarchic and democratic elements — the middle class rules, avoiding the extremes of the very rich (who become arrogant and lawless) and the very poor (who become servile and criminal). A large middle class produces the most stable regime.
11–16 1295a25–1301a19
Deliberative, executive, and judicial elements
The middle class is the best political base for stability because it is least prone to faction: the very rich and very poor are each others' enemies, and both are enemies of the middle. Political constitutions need three functional parts: (1) the deliberative element (decides war, peace, laws, alliances — the assembly or council), (2) the executive element (magistrates who administer day-to-day government), and (3) the judicial element (courts that adjudicate disputes and crimes). How each is organized determines the character of the regime. Democratic versions: lot, open qualification, large assemblies. Oligarchic versions: property qualification, election, small councils. Mixed constitutions blend these methods — using lot for some offices and election for others, combining property qualifications with open enrollment.
Book V: Revolution and stability
1–7 1301a19–1307b24
Causes of revolution — inequality and faction
The general causes of revolution (stasis) and constitutional change. The fundamental cause: perceived inequality and injustice — when those who consider themselves equal are treated unequally, or when those who are unequal demand equality they do not deserve. In democracies, revolutions arise from demagogues attacking the wealthy (driving them to unite and overthrow the democracy). In oligarchies, from the excluded masses demanding a share. Specific triggers: personal insults, fear of prosecution, contempt for the regime, disproportionate growth of one class, election intrigues, gradual imperceptible change (small concessions that cumulatively transform the constitution). The psychology of revolutionaries: they seek either profit or honor, and they are aroused by injustice, fear, contempt, or the spectacle of others gaining unjust advantage.
8–12 1307b25–1316b27
How to preserve constitutions; tyranny's instability
How to preserve constitutions. General rules: prevent any one individual or faction from becoming disproportionately powerful; rotate offices; combine oligarchic and democratic elements to satisfy both sides; maintain the rule of law above persons; educate citizens in the spirit of the constitution. Preservation of specific regimes: democracies survive by not confiscating wealth (which drives the rich to revolution); oligarchies by treating the excluded generously and maintaining internal solidarity among the elite. Tyranny — the most unstable regime — survives either by brutal repression (killing the able, prohibiting gatherings, using secret police) or by moderate self-limitation (appearing kingly, maintaining revenues without oppression, courting the people). On average, tyrannies last at most one or two generations.
Book VI: Organizing democracies and oligarchies
1–8 1316b31–1323a10
Institutional design for democracies and oligarchies
Practical handbook for constructing stable democratic and oligarchic constitutions. The principle of democratic freedom: ruling and being ruled in turn, and living as one likes. Democratic institutions: selection by lot, payment for office (enabling the poor to serve), short terms, no repeated tenure. How to organize the various magistracies (financial, military, market, urban, rural) in a democratic way. Oligarchic counterparts: property qualifications, fines for non-attendance by the wealthy to ensure they participate, special taxes on the rich to fund public services (offsetting popular resentment). The overarching theme: sustainable constitutions require institutional design that mitigates the natural tendency of each regime to become more extreme over time.
Book VII: The ideal city
1–3 1323a14–1325b32
The best life for individual and city
What is the best life — and does it differ for the individual and the city? The best life requires virtue and external goods (health, wealth, friends, good fortune) — but virtue is primary and self-sufficient while external goods have a natural limit beyond which excess is harmful. The best city aims at the same happiness as the best individual: virtue in action. Contra the imperialist view (that the best city is the most powerful), the best city pursues internal excellence rather than domination over others. The practical/political life and the philosophical/contemplative life are both compatible with the best state — but the city as a whole exercises practical virtue by maintaining justice, education, and noble institutions.
4–12 1325b33–1332b11
Population, territory, and the ideal citizen character
Material conditions of the ideal city. Population: large enough for self-sufficiency, small enough for mutual acquaintance and ordered government. Territory: large enough to support the population in leisure, with access to the sea (for trade and naval defense). Location: defensible, well-watered, healthy (facing east for sun; sheltered from north winds). Natural character of the citizens: the ideal populace combines the spiritedness (thumos) of northern peoples with the intelligence of Asians — as the Greeks do by geographical fortune. Social classes: farmers, artisans, warriors, wealthy, priests, judges/deliberators — but citizenship and rule should be restricted to those who possess virtue and leisure (warriors when young, deliberators when old, priests when elderly).
13–17 1332a38–1337a7
Education — body, then habit, then reason
Education is the legislator's chief task — for a constitution can only be preserved if the citizens' character matches it. Three elements of human goodness: nature (natural capacity), habit (training and habituation), and reason (instruction and deliberation). Education must follow nature's own development: first the body (physical training for the young), then the appetites (habituation in virtue), then the intellect (reasoned education). Children's upbringing: diet, exercise, appropriate stories and music; avoidance of vulgar speech and company. From age 7 to puberty: gymnastic training (not excessively brutal — Sparta's error) and literacy. The overall principle: education for leisure and noble activity, not merely for work or warfare.
Book VIII: Education
1–7 1337a11–1342b34
Public education, music, and the modes
Education must be public (the same for all citizens) and communal (not left to individual families) because each citizen belongs to the city, not to himself alone. What should be taught? The useful (reading, writing, drawing, gymnastics — for practical life), and the noble (music — for leisure and the development of character). Music receives extensive treatment: different modes (Dorian, Phrygian, Lydian) produce different emotional effects and shape character differently. The Dorian mode is the most stable and manly, suitable for education; the Phrygian is enthusiastic/ecstatic, suitable for catharsis; the Lydian is relaxing, suitable for the elderly. Musical instruments: the flute is rejected for education (it distorts the face, prevents speech while playing, and is too orgastic); the lyre is preferred as moderate and rational. The work breaks off abruptly — perhaps the rest is lost, or Aristotle never completed this section.
Athenian Constitution
The sole survivor of Aristotle's project of 158 constitutional studies. Lost for two millennia, rediscovered on papyrus in Egypt in 1879 (a fragment) and 1891 (the main text, now in the British Library).
Part I: Historical narrative (chs. 1–41)
1–11 Chs. 1–11
Draco, Solon, and the earliest constitutional history
From the earliest constitutional history recoverable. Cylon's attempted tyranny (c. 632) and the resulting curse on the Alcmaeonidae. Draco's legislation (c. 621): codified law but retained harsh penalties — 'his laws were written in blood.' Solon's reforms (594/3): the seisachtheia (shaking off of burdens — cancellation of debts, liberation of those enslaved for debt), the property-class system (pentakosiomedimnoi (500-bushel men), hippeis (horsemen), zeugitai (yoke-men), thetes (laborers)), the creation of the Council of 400, the popular courts, and the right of any citizen to bring suit on behalf of an injured party. Aristotle praises Solon's moderation: he gave the people enough power for self-defense but not enough for aggression.
12–22 Chs. 12–22
Tyranny, Cleisthenes' reforms, and the Persian Wars
The Peisistratid tyranny (561–510): Peisistratus seized power three times, finally ruling successfully by maintaining Solon's laws, fostering agriculture, and keeping the peace. His sons Hippias and Hipparchus continued until Harmodius and Aristogeiton murdered Hipparchus (514) and Hippias was overthrown by the Alcmaeonidae with Spartan help (510). Cleisthenes' reforms (508/7): the founding of radical democracy — reorganized Attica into ten tribes (phylai), each composed of demes from city, coast, and inland regions (mixing old regional loyalties). Created the Council of 500 (50 from each tribe), introduced ostracism. The Persian Wars (490–480) and the Areopagus's temporary prestige; Themistocles and the naval program.
23–32 Chs. 23–32
Radical democracy, the Peloponnesian War, oligarchic coups
The growth of radical democracy. After the Persian Wars, the Areopagus Council dominated (478–462). Ephialtes' revolution (462/1): stripped the Areopagus of its political powers, transferring them to the assembly, courts, and Council of 500 — this established full radical democracy. Pericles' additions: pay for jury service (enabling the poor to participate), restriction of citizenship to those of Athenian parentage on both sides. The Peloponnesian War (431–404): the strains of war led to oligarchic conspiracies. The oligarchic coup of 411: the Four Hundred seized power briefly, then the Five Thousand (a moderate oligarchy) ruled before democracy was restored.
33–41 Chs. 33–41
The Thirty Tyrants and the democratic restoration
The Thirty Tyrants (404–403): after Athens' defeat, Sparta installed an oligarchic junta led by Critias and Theramenes. They executed 1,500 citizens without trial and confiscated property wholesale. Theramenes opposed the extremists and was himself executed. Democratic exiles under Thrasybulus rallied at Phyle, seized Piraeus, and eventually restored democracy (403). The reconciliation agreement (a remarkable act of amnesty — 'no one shall bear malice for the past'). The constitution of Aristotle's own day (after 403): Aristotle counts eleven constitutional changes in Athenian history and sees the current moderate democracy as the final, stable settlement.
Part II: Contemporary institutions (chs. 42–69)
42–49 Chs. 42–49
Citizenship, the ephēbeia, and the Council of 500
Citizenship and its institutions. Registration in demes at age 18; the scrutiny (dokimasia) to verify parentage and age. The ephēbeia (civic military training): two years of military training for young citizens (first year at Piraeus, second patrolling the borders — equipped with spear and shield at state expense). The Council of 500 (Boulē): 50 members from each tribe, chosen by lot, serving for one year. The prytany system: each tribal group of 50 presides for one-tenth of the year. Powers of the Council: prepares the agenda for the assembly, oversees finances and magistrates, manages public buildings and the navy, and tries certain cases. The epistates (chairman) holds the state seal and keys for one day only — preventing any individual from accumulating power.
50–62 Chs. 50–62
Magistracies — archons, generals, financial officers
The magistracies (archai). Most are selected by lot from all citizens (a democratic principle — sortition gives all an equal chance). The nine archons: the eponymous archon (oversees family law, festivals of Dionysus), the basileus (king-archon — religious cases, ancient rites, homicide), the polemarch (originally military commander, by this period handles cases involving metics and foreigners), and the six thesmothetai (organize the courts, introduce legislative reviews). Ten generals (stratēgoi): elected (not chosen by lot) because military command requires expertise. Financial magistrates: the apodektai (receivers of revenue), kolakretai (disbursers), poletai (auctioneers of state contracts). Market officials (agoranomoi), grain-inspectors (sitophylakes), weights-and-measures inspectors (metronomoi).
63–69 Chs. 63–69
The law courts, jury allotment, and trial procedure
The law courts (dikastēria): the most distinctive institution of Athenian democracy. A panel of 6,000 jurors is enrolled annually by lot. For each trial day, jurors are assigned to specific courts by an elaborate allotment machine (klērōtērion — Aristotle describes its mechanism in detail) to prevent corruption and intimidation. Jury sizes: private cases 201 or 401 jurors; public cases 501 or more (up to 2,501 for the most important). Trial procedure: speeches by prosecution and defense within timed water-clock (klepsydra) limits, witness testimony, document readings. Voting: by bronze ballot-discs (solid = acquittal, hollow = conviction), deposited secretly in urns. Jury pay: three obols per day (established by Pericles, raised by Cleon). The account is invaluable as the most detailed ancient description of how Athenian courts actually functioned.
Rhetoric & Poetics
Rhetoric
The art of persuasion as a counterpart to dialectic. Covers the three modes of proof (ethos, pathos, logos), the emotions, virtues, and style of effective speech.
Book I: Rhetoric and proof
1–3 1354a1–1358b20
Three modes of persuasion and three genres of rhetoric
Rhetoric is the counterpart (antistrophos) of dialectic — both deal with probable matters accessible to everyone, not with a specialized subject-matter. Rhetoric is the faculty of observing in each case the available means of persuasion. Previous writers on rhetoric focused only on arousing emotions in the audience; Aristotle insists that the core of rhetoric is proof — specifically the enthymeme (rhetorical syllogism from probable premises), which he calls 'the body of proof' (sōma tēs pisteōs). Three modes of persuasion: (1) ethos — the character of the speaker as it appears in the speech; (2) pathos — putting the audience into a certain emotional state; (3) logos — the argument itself, proving or seeming to prove. Three genres of rhetoric: deliberative (advising about future action — expediency), forensic/judicial (accusing or defending regarding past action — justice), epideictic/display (praising or blaming regarding present qualities — honor/beauty).
4–15 1359a30–1377b12
Topics for deliberative, forensic, and epideictic speech
Specific topics for each genre. Deliberative rhetoric: the orator must know about finance, war and peace, defense, imports/exports, and legislation — the kinds of knowledge a statesman needs. What promotes happiness and its components (good birth, friends, wealth, health, beauty, strength, good fortune, virtue). Forensic rhetoric: causes of wrongdoing (people do wrong from desire for pleasure, honor, or gain when they think they can escape detection or punishment or that the profit exceeds the penalty). Who commits injustice and against whom. What constitutes written and unwritten law. Epideictic rhetoric: the virtues (justice, courage, temperance, magnificence, magnanimity, liberality, wisdom, prudence) and how to amplify them through comparison. Common topics applicable to all three genres: the possible/impossible, past/future fact, and degree (greater/lesser).
Book II: Emotions and character
1 1377b16–1378a30
Ethos — wisdom, virtue, and goodwill
The three speaker-qualities that produce persuasion via ethos: practical wisdom (phronēsis — the audience believes the speaker knows what they're talking about), virtue (aretē — they trust the speaker's motives), and goodwill (eunoia — the speaker appears to wish the audience well). A speaker who manifests all three will be believed even without proof. The rest of Book II systematically provides the knowledge needed to manipulate pathos and deploy character-types in argument.
2–11 1378a31–1388b30
The emotions — anger, fear, shame, pity, envy
A systematic treatise on the emotions (pathē) — the first such work in Western thought. For each emotion, Aristotle specifies: (1) what state of mind disposes a person to feel it, (2) toward whom it is directed, (3) on what grounds. Anger (orgē): a desire for conspicuous revenge for a perceived slight — directed at individuals, not at classes. Calm (praotēs): the settling of anger when the slight is seen as unintentional or the offender repents. Fear (phobos): pain at the prospect of imminent evil — we fear what has the power to destroy us. Confidence (tharsos): the absence of feared dangers. Shame (aischunē): pain at present, past, or future evils that seem to bring dishonor. Pity (eleos): pain at apparent evil befalling someone who does not deserve it, when we feel it could happen to us. Indignation (nemesis): pain at undeserved good fortune in others. Envy (phthonos): pain at deserved good fortune in those like us.
12–17 1388b31–1391b7
Character by age and fortune — youth, old age, prime
Character (ēthos) as it varies with age and fortune — a brilliant piece of practical psychology. Youth: passionate, impulsive, hopeful, trusting, brave (from inexperience of evil), honorable, shame-sensitive, idealistic. Old age: cautious, suspicious, cynical, small-minded, cowardly (from experience of failure), self-interested, living by memory rather than hope. The prime of life: a balance of youth's spirit and age's prudence — roughly age 30–35 for body, 49 for mind. Character as affected by fortune: wealth produces arrogance and softness; power produces ambition and a sense of superiority; good birth produces contempt for others. The orator must know these types to frame arguments that appeal to each audience.
18–26 1391b8–1403a16
Enthymemes, examples, and lines of argument
The argumentative core of Book II: logos. The enthymeme (enthumēma): a syllogism from probable premises (eikota) or signs (sēmeia), in which one premise is often left unstated because the audience supplies it. Types of signs: infallible (tekmēria — blood on hands = violence), fallible (this person has a fever; pregnant women are pale). The example (paradeigma): rhetorical induction — citing historical parallels or invented parables. Twenty-eight lines of argument (topoi) for constructing enthymemes: from opposites, from more and less, from definition, from consequences, from cause, from turning the opponent's argument against them, etc. Nine apparent enthymemes (fallacies): homonymy, composition, exaggeration, the sign-fallacy. These chapters are the most technical part of the Rhetoric and show its continuity with the Topics and Analytics.
Book III: Style and arrangement
1–12 1403b6–1414a29
Style — clarity, metaphor, rhythm, vividness
Style (lexis): the art of saying the right thing in the right way. The chief virtue of style is clarity (saphēneia) — speech must be understood. Secondary virtue: appropriate elevation — neither too grand (bombastic) nor too humble (trivial), but fitting the subject. Metaphor (metaphora) is the most important device: it gives clarity, pleasure, and an impression of intelligence. Good metaphors reveal genuine likenesses (well-chosen analogies). Other stylistic devices: simile (explicit comparison), antithesis (balanced opposition), energeia (vividness — making the audience 'see' the thing), periodic sentences (balanced clauses that satisfy the ear), prose rhythm (not verse, but rhythmic patterns — the paeanic rhythm is best for prose). Foreign words and coinages should be used sparingly; clear, ordinary language is the foundation.
13–19 1414a30–1420a8
Arrangement — introduction, narrative, proof, epilogue
Arrangement (taxis): the parts of a speech. Minimally, every speech requires two parts: statement (prothesis — what you claim) and proof (pistis — the evidence). In practice, four parts: (1) introduction (prooimion — to win attention and goodwill; in forensic speeches, to state the case; in deliberative speeches, to preview the argument); (2) narrative (diēgēsis — statement of facts; should be brief, clear, and relevant — not everything that happened, but what matters for the proof); (3) proof (pistis — the arguments supporting your case, with refutation of the opponent); (4) epilogue (epilogos — recapitulation, amplification of your side, diminution of the opponent's, and arousing the audience's emotions for a final time). Each genre has its preferred emphasis: deliberative speeches stress proof; forensic speeches stress narrative and proof; epideictic speeches stress amplification.
Poetics
Aristotle's theory of literature — primarily tragedy. Introduces concepts of mimesis, catharsis, plot (mythos), and the six elements of tragedy. A second book on comedy is lost.
Chapters 1–5: Mimesis and forms of poetry
1–3 1447a8–1448a24
All poetry as mimēsis — means, objects, manner
All forms of poetry (epic, tragedy, comedy, dithyramb, music for aulos (double-pipe) and kithara (lyre)) are modes of mimēsis (imitation/representation) — they differ in three respects: (1) the means of imitation (rhythm, language, melody — used separately or in combination), (2) the objects of imitation (people better than us, worse than us, or like us), and (3) the manner of imitation (narrative in one's own person, narrative through characters speaking, or direct dramatic presentation). These three variables generate all the existing forms of literature and performance. Homer and Sophocles both imitate 'people better than us,' but Homer narrates while Sophocles presents directly through actors. Comedy imitates people worse than us; tragedy and epic imitate people better.
4–5 1448b4–1449b20
Origins of poetry in human nature
The origins of poetry in human nature: mimēsis is natural to humans from childhood (we learn our first lessons through imitation) and we take pleasure in recognizing imitations. Poetry split into two branches according to the character of the poets: serious-minded poets imitated noble actions (hymns, encomia → epic → tragedy), while lighter poets imitated the actions of the ignoble (invectives → iambic → comedy). Tragedy evolved from improvisations by leaders of the dithyramb; comedy from leaders of phallic songs. Historical development of tragedy: Aeschylus introduced the second actor and reduced the chorus; Sophocles added the third actor and scene-painting. Epic differs from tragedy in length (epic is unlimited in time) and meter (epic uses hexameter only; tragedy uses varied meters), but both imitate serious subjects.
Chapters 6–12: Tragedy defined
6 1449b21–1450b20
Tragedy defined; plot as the soul of tragedy
The famous definition: tragedy is the imitation of an action that is serious (spoudaia), complete (teleia), and of a certain magnitude (megethos); in language embellished with each kind of artistic ornament applied separately in its parts; in dramatic rather than narrative form; through pity (eleos) and fear (phobos) effecting the catharsis (purification) of such emotions. Six constituent elements, in order of importance: (1) plot (mythos — the arrangement of incidents), (2) character (ēthos), (3) thought (dianoia — the intellectual content), (4) diction (lexis — the verbal expression), (5) melody (melos), (6) spectacle (opsis). Plot is 'the soul of tragedy' — without plot there is no tragedy, but there can be tragedy with minimal character-portrayal. A good plot must have beginning, middle, and end, and be of appropriate length (graspable by memory).
7–11 1450b21–1452b13
Unity, reversal, recognition, and complex plots
Plot structure in detail. A proper magnitude: long enough to allow a probable or necessary sequence from misfortune to good fortune (or vice versa), short enough to be grasped as a unity. Unity of plot: not unity of hero (not everything that happens to one person), but unity of action — events connected by probability or necessity so that removing any one would dislocate the whole. Simple vs. complex plots: simple plots have a continuous movement without reversal or recognition; complex plots (superior) include reversal (peripeteia — a change to the opposite of what was intended, e.g., the messenger coming to comfort Oedipus reveals his true parentage) and/or recognition (anagnōrisis — a change from ignorance to knowledge, producing love or hatred). The finest tragedies combine both reversal and recognition in a single event.
12 1452b14–1452b27
Quantitative parts — prologue, episode, exode, chorus
The quantitative parts of tragedy (as opposed to the qualitative elements of ch. 6): prologue (everything before the first choral entry), episode (a complete section of dialogue between choral songs), exode (everything after the last choral song), and the choral parts — parodos (the first full choral song) and stasimon (subsequent choral songs without anapaests or trochees). A brief schematic classification to be distinguished from the qualitative analysis that dominates the rest of the work.
Chapters 13–22: Craft and diction
13–14 1452b28–1454a15
The ideal tragic hero and hamartia
The ideal tragic plot: what kind of change of fortune produces the strongest pity and fear? Not a thoroughly good person falling from good fortune to bad (merely shocking, not tragic); not a thoroughly bad person rising from bad to good (not pitiable, not fearful, not satisfying); not a villain falling (satisfying but not tragic — no pity). The ideal protagonist: a person 'like us' or 'better than us' who falls through some error (hamartia) — not through vice or wickedness but through a mistake or misjudgment. (The popular rendering 'tragic flaw' is misleading; most scholars hold that Aristotle's hamartia denotes an intellectual error or misjudgment rather than a character defect, though this remains debated.) Examples: Oedipus, Thyestes. The best recognition is one where the fear and pity arise from the plot-structure itself (the logic of events), not from spectacle (stage effects are a crude substitute for good writing).
15–18 1454a16–1456a32
Character requirements and six types of recognition
Character in tragedy: four requirements. (1) The character must be good (chrēstos) — possessing moral purpose appropriate to their type (even a woman or slave can be good in their sphere). (2) Appropriate (harmoton) — manliness is appropriate for a warrior but not for a woman character. (3) Likeness (homoion) — the character should be recognizable as human. (4) Consistent (homalon) — if inconsistent, consistently inconsistent. Recognition (anagnōrisis): six types ranked from worst to best — by tokens/signs, contrived by the poet, through memory, through reasoning, through compound inference, and best of all through the incidents themselves (as in Oedipus). The proper length of a tragedy and how to construct complex plots with multiple reversals.
19–22 1456a33–1459a16
Diction, metaphor, and Homer's supreme style
Thought (dianoia): the intellectual content of speeches — how characters prove, refute, arouse emotions, amplify, or diminish. For this, see the Rhetoric. Diction (lexis): the art of verbal expression. The elements of language: letter (stoicheion), syllable, conjunction, noun, verb, case, sentence. Types of nouns: standard (kurios — ordinary language), foreign (glōtta — from another dialect or language), metaphor (transfer from genus to species, species to genus, species to species, or by analogy), coined word (pepoiēmenon), lengthened, curtailed, altered. The excellence of diction: clear without being pedestrian. Metaphor is the greatest sign of genius — it cannot be taught, because seeing likenesses between dissimilar things requires a natural eye for resemblance. Homer's supreme achievement in diction.
Chapters 23–26: Epic
23–24 1459a17–1460a26
Epic — unity of action and Homer's supremacy
Epic poetry shares with tragedy the requirement of unity of action (not unity of hero, not unity of time-period). Homer is praised above all other poets for understanding this: the Iliad and Odyssey each focus on a single action (the wrath of Achilles, the return of Odysseus) and incorporate other events only insofar as they contribute to that action — unlike cyclic poets who tried to narrate the entire Trojan War. Epic differs from tragedy in permitting greater length (multiple simultaneous actions can be narrated) and in admitting the wonderful/irrational more easily (because we do not see the events but only hear them described — what would be absurd on stage passes in narrative).
25–26 1460a27–1462b18
Solving Homeric problems; tragedy surpasses epic
How to solve critical problems (luseis) in Homer: alleged impossibilities, irrationalities, contradictions, improprieties, and technical errors. Solutions: the poet imitates things as they are, as they are said to be, or as they ought to be; a metaphor or obsolete usage may be mistaken for an error; what seems contradictory may refer to different aspects of the situation. Chapter 26: which is the superior art — epic or tragedy? Against those who think epic is more dignified: tragedy has everything epic has (meter, narrative possibility, diction, thought) plus two additional pleasures (music and spectacle), is more concentrated and unified (achieves its effect in a shorter time), and has greater vividness. Therefore tragedy is the superior art. The text breaks off; the promised second book on comedy is lost.
Lost Book II: On comedy
—
The lost second book on comedy
Aristotle planned or composed a parallel treatment of comedy. The Poetics itself refers to a future discussion of comedy and iambic poetry ('we will speak of these later'). Now lost — either it perished in the general loss of Aristotle's library, or Aristotle never completed it. The 10th-century Tractatus Coislinianus (a Byzantine manuscript) may preserve a much-condensed outline: it defines comedy as an imitation of an action that is ludicrous and imperfect, through pleasure and laughter effecting the catharsis of such emotions. It lists comic plot-types, comic characters, and comic diction. Whether this reflects Aristotle's actual views or is a later student construction remains debated.
Lost & Disputed
Lost Works (Exoteric Writings)
Aristotle's published works for general readers — mainly Platonic-style dialogues — were widely admired in antiquity. Cicero called his style 'a river of gold'. None survive intact.
LostAll lost. Knowledge comes from fragments quoted in Cicero, Plutarch, Iamblichus, Alexander of Aphrodisias, and other ancient authors.
Major lost dialogues
Eudemus
On the soul and its immortality
On the soul. Argued for its immortality in a more Platonic vein than the surviving De Anima — possibly including arguments for the soul's pre-existence and recollection of a prior life. Written on the occasion of the death of Aristotle's friend Eudemus of Cyprus (c. 354 BCE). Cicero reports that it was written 'in imitation of Plato's Phaedo.' The fragments suggest a young Aristotle still working within a Platonic framework but beginning to develop his own views on the soul-body relationship. Its doctrine of immortality was contrasted with De Anima's hylomorphism by later commentators (Alexander, Simplicius) who debated whether Aristotle changed his mind.
Protrepticus
An exhortation to the philosophical life
An exhortation to philosophy (protreptic = 'turning toward') addressed to Themison, a ruler in Cyprus. Argues that philosophy is not merely one pursuit among others but the highest and most necessary activity: all other goods (wealth, power, health) are good only if used wisely, and wisdom alone can direct them well. Substantial fragments preserved by Iamblichus (who copied long passages into his own Protrepticus) enable partial reconstruction. Key arguments: the practical value of theoretical knowledge (the astronomer is more useful to navigation than the experienced sailor); the life of contemplation as the proper end of human nature; 'we should philosophize' is established even by the attempt to refute it (since that attempt is itself philosophizing).
On Philosophy
History of wisdom, critique of Forms, natural theology
Three-book dialogue on the history and nature of philosophy. Book I: the history of wisdom from the Magi and Egyptians through the Greeks. Book II: critique of Plato's Theory of Forms and Ideas-Numbers (important evidence for Plato's 'unwritten doctrines'). Book III: Aristotle's own positive theology — arguments for the existence of the divine from the regularity of celestial motions, from the graduated perfection of beings, and from human experience of prophetic dreams and the soul's powers at the moment of death. This work was widely read in antiquity and influenced Stoic theology and Cicero's De Natura Deorum. Its arguments anticipate both Physics VIII and Metaphysics XII.
On the Good
Plato's oral lecture recorded and critiqued
Records and critiques Plato's oral lecture 'On the Good' (peri tagathou), which famously disappointed its audience by being entirely about mathematics. Aristotle's account is a key source for Plato's 'unwritten doctrines' — the derivation of all things from the One and the Indefinite Dyad. Several students (Speusippus, Xenocrates, Heraclides, Hestiaeus) reportedly took notes; Aristotle's version was apparently the most complete and critical. Fragments preserved in Simplicius and Alexander suggest Aristotle objected that mathematical principles cannot serve as causes of sensible things.
On Ideas
Systematic critique of the Theory of Forms
A systematic critique of the Theory of Forms — more technical than the polemic in Metaphysics I and XIII. Important fragments preserved by Alexander of Aphrodisias in his commentary on the Metaphysics. Contains the 'Third Man' argument in its most rigorous logical form, the 'argument from relatives' (if we posit Forms for things that have relatives, we must posit Forms of relations themselves — leading to absurdities), and arguments from the sciences (if scientific knowledge requires Forms, then there must be Forms corresponding to every predicate, including negations and artifacts). Probably composed during Aristotle's time in the Academy while Plato was alive.
On Justice (4 books)
The nature of justice and the ideal community
A major early dialogue in four books, possibly Aristotle's counterpart to Plato's Republic. The fragments suggest it discussed: the nature of justice, the relationship between justice and law, whether the just life is happier than the unjust, and the ideal political community. Cicero and Lactantius quote from it; some scholars attempt to reconstruct its argument from parallels in NE V and Politics III. Its four-book length suggests it was among the most substantial of the lost dialogues, rivaling the Protrepticus and On Philosophy in scope and ambition.
Other dialogues
On Poets, Rhetoric, Wealth, Prayer, Nobility, and more
On Poets (at least 2 books — discussed Homer, the pre-Socratic poets, and the function of poetry; related to the Poetics but more historical). On Rhetoric / Gryllus (critiqued existing rhetorical handbooks; named for Xenophon's son who died at Mantinea). On Wealth (argued that wealth is a means, not an end). On Prayer (discussed whether petitionary prayer is coherent given divine nature). On Nobility (eugeneia — discussed whether noble birth confers genuine advantage or merely reputation). On Pleasure. On Education. All lost except for isolated quotations in later authors — collectively they represent the accessible, polished literary side of Aristotle that made him famous in antiquity.
Other lost works
Constitutions
158 constitutional studies; only the Athenian survives
A vast comparative-politics project: Aristotle and his students collected and analyzed 158 constitutions of Greek and non-Greek states. Only the Athenian Constitution survives. Ancient catalogues list constitutions of Sparta, Corinth, Crete, Aegina, Thessaly, and many others. Each reportedly contained a historical narrative followed by a description of current institutions (as in the surviving Athenian example). The project provided the empirical basis for the Politics — its theoretical conclusions about constitutional types, revolutions, and stability rest on this massive dataset. Fragments are quoted by lexicographers, scholiasts, and historians throughout antiquity.
Homeric Problems
Six books of scholarly commentary on Homer
Six books of detailed scholarly commentary addressing difficulties (problēmata) in Homer's Iliad and Odyssey — apparent contradictions, obscure usages, implausible events. Fragments show Aristotle resolved problems by appealing to obsolete word-meanings, variant readings, speaker-context (a character's statement need not reflect the poet's view), and the principle that poetry aims at the probable rather than the actual. This work was foundational for the Hellenistic tradition of literary scholarship in Alexandria (Aristarchus and others continued the method). Some material is preserved in the Byzantine scholia on Homer and in Porphyry's Homeric Questions.
Records
Pythian victors, Olympic lists, and dramatic records
Aristotle (with his nephew Callisthenes) compiled the list of victors at the Pythian Games (the Pythionikai) and contributed to the compilation of Olympic victor lists. He also compiled records of dramatic performances (didascaliai) at the Athenian Dionysia — who produced what play, when, with what result. These chronological reference works were fundamental to Greek historical dating and literary history. The Pythian victor-list required research at Delphi; the didascaliae drew on Athenian archives. Both projects exemplify Aristotle's commitment to systematic collection of empirical data as the foundation for theoretical work.
Spurious & Doubtful Works
Numerous works transmitted under Aristotle's name in the medieval manuscripts are now generally judged to be by his students, by later Peripatetics, or by unrelated authors.
SpuriousThese works are in the traditional corpus but not by Aristotle himself. They range from valuable Peripatetic works (Problems, Mechanics) to clearly later compositions.
Probably Peripatetic compilations
Problems
~900 scientific questions in 38 books
Bekker 859a–967b. About 900 scientific questions ('why does...?') organized in 38 books covering medicine, acoustics, optics, meteorology, botany, music, mathematics, ethics, and physiology. Questions and answers are brief (typically a paragraph). Many display genuine Aristotelian methodology (explaining phenomena through the four causes), and some may derive from Aristotle's own teaching. But the collection was clearly expanded over generations by Peripatetic students and later compilers — internal inconsistencies, varying levels of sophistication, and post-Aristotelian references make single authorship impossible. It remains invaluable as a window into the research program of the Lyceum.
Mechanics
Theoretical mechanics from the principle of the lever
Bekker 847a–858b. The earliest surviving treatise on theoretical mechanics. Begins from the principle of the lever (longer arm moves with greater force) and applies it to the wheel, the wedge, the pulley, the balance, oars, rudders, nutcrackers, and other mechanisms. The theoretical framework: all mechanical effects reduce to properties of the circle — points on a larger circle move faster than points on a smaller. Likely by an early Peripatetic — perhaps Strato of Lampsacus (head of the Lyceum after Theophrastus) or another student with strong mathematical interests. The work influenced Archimedes and became foundational for Renaissance mechanics.
Generally judged spurious
On the Universe
A theological cosmology addressed to Alexander
Bekker 391a–401b. A theological cosmology addressed to 'Alexander' — in the style of a letter from Aristotle to his former student. Describes the cosmos in grandiloquent Stoic-influenced language: God pervades all things as a sustaining power, seated at the summit of the cosmos but acting through all levels of being. The style, vocabulary, and philosophical content point to the 1st century BCE — probably a Middle Platonist or eclectic philosopher writing under Aristotle's name to give authority to a synthesis of Peripatetic cosmology and Stoic theology. Nevertheless, it was widely read in late antiquity and the Islamic world.
On Colors
Simple colors, mixtures, and light in media
Bekker 791a–799b. Discusses the nature of colors: simple colors (white and black) and their mixtures. Colors arise from the interaction of light with the transparent medium and with surfaces. Likely by Theophrastus or Strato — the theory is consistent with Aristotle's De Sensu but develops it in directions more characteristic of Theophrastus's systematic empiricism. The work shows sophisticated observation of color phenomena (mixing, reflection, refraction through different media) and attempts physical explanations involving the interaction of fire (light) with air and water.
On Things Heard
Acoustics — production and quality of sounds
Bekker 800a–804b. A short treatise on acoustics: the production, transmission, and quality of sounds. Discusses why some voices are clear and others rough, why sounds differ in pitch, and how echoes arise. The physical theory (sound as a motion of air, varying with the force and shape of the striking body) is broadly Peripatetic. The work is too brief and lacks the argumentative structure characteristic of Aristotle — more likely a set of teaching notes or student compilation from the Lyceum's acoustics research.
Physiognomonics
Inferring character from physical appearance
Bekker 805a–814b. The art of inferring character from physical appearance: bodily signs (hair color, eye shape, gait, voice quality) are correlated with character traits. Three methods: (1) inferring from animal resemblances (aquiline nose → nobility, like an eagle), (2) from ethnic types (Egyptians are shrewd, Thracians are brave), (3) from emotional expressions (anger reddens the face; therefore a ruddy person is prone to anger). Aristotle mentions physiognomics favorably in Prior Analytics II.27 and History of Animals I.8–9, but this treatise is likely by an early Peripatetic who developed the hints into a systematic manual.
On Plants
Classification of plants via Arabic and Latin translations
Bekker 815a–830b. Aristotle wrote a genuine botanical work, but it is lost (Theophrastus's botanical works largely supplant it). This surviving text is a medieval Latin translation of an Arabic translation of a Greek original — probably by Nicolaus of Damascus (1st century BCE), a Peripatetic philosopher and historian. The content is a general classification of plants and their parts, reproduction, growth, and nutrition — drawing on Theophrastus but much simplified. The double translation makes the Greek original nearly unrecoverable.
On Marvelous Things Heard
Geographical and natural curiosities
Bekker 830a–847b. An anonymous Hellenistic miscellany of geographical and natural curiosities — wonders, paradoxes, and marvels from around the Mediterranean and beyond. Hot springs, strange animals, unusual ores, rivers that petrify objects, islands with peculiar properties. No argumentative structure; purely a collection of peri thaumasiōn ('about wonders'). Compiled gradually from the 3rd century BCE onward by various hands, drawing on earlier paradoxographical collections. Attributed to Aristotle solely because it entered the corpus at some point in its transmission history.
On Indivisible Lines
Refutation of Xenocrates' minimal magnitudes
Bekker 968a–972b. Refutes the doctrine of 'indivisible lines' (atomoi grammai) attributed to Xenocrates — the claim that there are minimal magnitudes that cannot be further divided. The refutation uses Aristotelian principles about continuity and divisibility (from Physics VI). Possibly by Theophrastus: the method and interests align with his known works on mathematical and physical topics. Alternatively, an early Peripatetic student working through the school's official position against Academic mathematics.
On Winds
Wind directions and their characteristics
Bekker 973a–973b. An extremely short geographical fragment (barely one Bekker page) on wind directions and their characteristics. Too brief to judge authorship definitively — possibly a fragment of a longer work, possibly notes from a lecture. The content is consistent with Meteorologica II but adds nothing substantial.
On Melissus, Xenophanes, Gorgias
Doxography of three Presocratic thinkers
Bekker 974a–980b. A doxographical work presenting and critiquing the doctrines of three Presocratic thinkers: Melissus (monism, denial of motion), Xenophanes (theology, epistemology), and Gorgias (his nihilistic treatise 'On Non-Being'). Authorship much debated: some assign it to Aristotle himself (early period, possibly lecture notes from the Academy), others to a later Peripatetic (Theophrastus or a student). The treatment is competent but compressed — more a summary for teaching purposes than a polished philosophical work.
Rhetoric to Alexander
Practical rhetorical handbook by Anaximenes
Bekker 1420a–1447b. A complete and practical rhetorical handbook — how to compose deliberative, epideictic, and forensic speeches; techniques of proof and amplification; the parts of a speech. Almost certainly by Anaximenes of Lampsacus (a contemporary of Aristotle and tutor to Alexander), not by Aristotle himself. The work lacks Aristotle's theoretical framework (no discussion of enthymeme, no emotional analysis, no systematic logic of proof) and follows the older pre-Aristotelian handbook tradition. It entered the corpus because of its prefatory letter (probably forged) addressing Alexander.
On Virtues and Vices 1249a26–1251b37
Schematic catalogue of virtues and their vices
Bekker 1249a–1251b. A schematic catalogue of virtues, vices, and their characteristic actions. Lists the cardinal virtues — prudence (phronēsis), justice (dikaiosunē), courage (andreia), temperance (sōphrosunē) — and adds several others: liberality, magnanimity, gentleness, wisdom. For each virtue, the corresponding vices of excess and deficiency are named, and the typical actions of each are listed in brief clauses (e.g., 'it belongs to courage to be undismayed by fears of death'). No philosophical argumentation or defense of the classifications — purely descriptive and definitional. The style is formulaic and scholastic rather than discursive, and the philosophical vocabulary occasionally departs from standard Aristotelian usage, suggesting a post-Aristotelian compiler working within a broadly Peripatetic-Platonic tradition rather than Aristotle himself. Almost universally regarded as spurious — probably composed by an eclectic Hellenistic or early Imperial author.