Aristotle - Introduction and Epicurean Guide

Why Aristotle Matters to Epicureans

Aristotle (384–322 BC) is one of the most influential philosophers in the history of the West. For twenty years he studied in Plato’s Academy. He then tutored the young Alexander of Macedon, and in 335 BC he founded his own school at Athens, the Lyceum, whose members came to be called Peripatetics. His surviving works fill a shelf of volumes and cover nearly every subject: logic, physics, astronomy, biology, the soul, metaphysics, ethics, politics, rhetoric and poetry. Thomas Aquinas built Catholic theology on his foundations, and Dante, who placed Epicurus among the heretics in Hell, honored Aristotle as the master of those who know.

Epicurus (341–270 BC) was born when Aristotle was forty-three. The two men never debated in person, but their lives overlapped. Diogenes Laertius records that Epicurus came to Athens in his eighteenth year, “when Xenocrates was at the Academy and Aristotle was living in Chalcis” (DL X.1). Aristotle had withdrawn to Chalcis after the death of Alexander, and he died there the following year. When Epicurus opened his own school in Athens in 307/306 BC, the Lyceum was flourishing under Aristotle’s successor Theophrastus. For the whole of Epicurus’s teaching life, Aristotle’s school was one of the two great established schools of the city, the other being Plato’s Academy. Their teaching was the philosophical establishment that Epicurus set out to overturn.

Aristotle matters to Epicureans for three main reasons.

First, Aristotle was a major builder of the system that Epicurus attacked. Plato left behind dialogues, myths and questions. Aristotle turned them into a complete account of the world, worked out subject by subject. In that account the universe is a single, finite, eternal sphere. There is no void. Matter is not made of atoms. The heavens are made of a divine fifth element and move in perfect circles forever. Their motion is caused by a god who is pure thought and who moves the world as an object of love. Nature does nothing in vain, and every living thing exists for the sake of an end. The highest part of the human soul is divine and immortal. Happiness is the activity of the soul in accordance with virtue, and the best life is spent in contemplating the eternal. Pleasure is welcome only when it follows from the right activity, and the man who makes pleasure his goal is called a slave who prefers “a life suitable to beasts.” Point by point, this is the world that Epicurus denied.

Second, Aristotle’s system outlived Epicurus’s by more than a thousand years. When the ancient world gave way to the Christian one, Epicurus was condemned and his books were lost. Aristotle was taken up, first by Islamic and Jewish philosophers and then by the Latin Church. His unmoved mover became the God of the theologians, and his account of the soul was made to support its immortality. His ethics of virtue and contemplation was fitted to the Christian life. Much of what Epicureans today must argue against comes to us in Aristotle’s words or by way of his arguments.

Third, Aristotle is the opponent most often mistaken for an ally. Many modern readers think of Aristotle as the down-to-earth student who turned away from Plato’s other-worldly Forms toward the study of nature and the evidence of the senses. Raphael’s famous painting The School of Athens (1511) shows Plato pointing up to the heavens and Aristotle holding his hand flat toward the earth. From this picture it is a short step to the idea that Aristotle and Epicurus were natural allies against Plato, both scientists and both “empiricists.” This picture is badly mistaken. On every question that mattered most to Epicurus, Aristotle stood with Plato against Democritus, and Epicurus stood against them both.

The rest of this introduction surveys what Aristotle taught about each of the three divisions of Epicurean philosophy: the Canon, or how we know the truth; Physics, or the nature of things; and Ethics, or how to live. Each section states Aristotle’s position in his own words, with links to the passages in the full translations on this site, and then sets out the Epicurean response. The works themselves follow, each with an Epicurean guide of its own and a linked chapter-by-chapter outline:

Posterior Analytics: scientific knowledge and demonstration.
Physics: nature, cause, chance, the infinite, place, void, time, motion and the first mover.
On the Heavens: the single, finite and eternal heaven, the fifth element, the elements and their natural places.
On Generation and Corruption: coming to be and passing away, and the case against the atomists.
On the Soul: the soul as the form of the body, sensation, imagination and intellect.
On Sense, Memory, Sleep and Dreams: five of the short natural treatises, including Aristotle’s account of prophetic dreams.
Metaphysics: “first philosophy,” Aristotle’s history of the earlier philosophers, and his god.
Nicomachean Ethics: happiness, virtue, pleasure, friendship and the contemplative life.

Aristotle and Epicurus: The Historical Record

What Epicurus Said About Aristotle

Only a little of what Epicurus wrote about Aristotle survives, and none of it is friendly. Diogenes Laertius lists the names Epicurus gave to rival philosophers. He called “Plato himself ‘The golden man,’ and Aristotle ‘The debauchee,’ saying that he devoured his inheritance and then enlisted and sold drugs” (DL X.8). Athenaeus fills in the story from Epicurus’s letter On Vocations: “after he had devoured his inheritance he entered the army, and on meeting with poor success in the campaign he betook himself to drug-selling. Afterwards, Epicurus says, Plato opened his school, and Aristotle went so far as to hazard himself there, and attended the lectures, being no dullard, and gradually assumed the contemplative habit” (Usener 171).

Athenaeus remarks that Epicurus is the only source for these stories, but the barb at the end is worth noticing. For Aristotle the contemplative life was the highest and most divine life a man could live. Epicurus presents it as the last stop of a drifting young man who had failed at everything else. The insult is aimed at the very thing Aristotle valued most.

The Epicurean Spokesman Velleius on Aristotle’s God

One of the fullest Epicurean criticisms of Aristotle that survive is in Cicero’s dialogue On the Nature of the Gods. There the Epicurean Velleius reviews the theology of the earlier philosophers and turns to Aristotle’s lost work On Philosophy:

“And Aristotle in the Third Book of his Philosophy has a great many confused notions, <not> disagreeing with the doctrines of his master Plato; at one moment he assigns divinity exclusively to the intellect, at another he says that the world is itself a god, then again he puts some other being over the world, and assigns to this being the rôle of regulating and sustaining the world-motion by means of a sort of inverse rotation; then he says that the celestial heat is god — not realizing that the heavens are a part of that world which elsewhere he himself has entitled god. But how could the divine consciousness which he assigns to the heavens persist in a state of such rapid motion? Where moreover are all the gods of accepted belief, if we count the heavens also as a god? Again, in maintaining that god is incorporeal, he robs him entirely of sensation, and also of wisdom. Moreover, how is motion possible for an incorporeal being, and how, if he is always in motion, can he enjoy tranquillity and bliss?” (Cicero, On the Nature of the Gods I.33, tr. Rackham)

Two points stand out. Velleius classes Aristotle with Plato’s school (“not disagreeing with the doctrines of his master Plato”), right before turning to Plato’s other pupils Xenocrates and Heracleides. And he puts his finger on the problem that runs through all of Aristotle’s theology: a god who has no body, who is busy turning the heavens, or who is the heavens, cannot also be a blessed living being who enjoys his own existence. For the Epicurean, a god must be a living being that is happy, and happiness belongs to beings that perceive and enjoy.

The Stoics Took Over Aristotle’s Arguments for Divine Stars

In the second book of the same dialogue, the Stoic Balbus makes his case that the world is governed by divine providence, and he leans on Aristotle again and again. He cites Aristotle’s argument that living creatures must be born in the heavens, so that “the stars occupy the region of aether, and as this has a very rarefied substance and is always in lively motion, it follows that the animal born in this region has the keenest senses and the swiftest power of movement” (ND II.42). He praises Aristotle’s argument that since the stars move neither by nature nor by force, “it remains therefore that the motion of the heavenly bodies is voluntary” (ND II.44). And he quotes at length Aristotle’s famous picture of men who had always lived underground, who come up into the light, see the earth, the sea and the sky, and conclude at once that “the gods exist and that these mighty marvels are their handiwork” (ND II.95).

None of these three passages survives in Aristotle’s own writings. All three come from his dialogue On Philosophy, which is lost. They are known only because Cicero reported them, and they are printed among the fragments of that dialogue in Valentin Rose’s standard collection, Aristotelis qui ferebantur librorum fragmenta (Leipzig: Teubner, 1886). The men who lived underground are fragment 12 (p. 29), and the arguments about the stars are fragments 23 and 24 (p. 38). Sextus Empiricus preserves another passage from the same lost work, in which “Aristotle said that the conception of Gods arose amongst mankind from two originating causes, namely from events which concern the soul and from celestial phenomena” (Sextus, Against the Physicists I.20). The surviving works translated here carry the same theology forward: the eternal first mover of the Physics (Book VIII) and the Metaphysics (Book XII), and the living, divine heavens of On the Heavens.

Epicurus answered exactly these claims. In the Letter to Herodotus he writes that the motions of the heavenly bodies “must not be thought to be due to any being who controls and ordains or has ordained them and at the same time enjoys perfect bliss together with immortality,” and that we must not believe that the heavenly bodies, “which are but fire agglomerated in a mass, possess blessedness, and voluntarily take upon themselves these movements” (DL X.77). The phrase “voluntarily take upon themselves these movements” answers the Aristotelian argument for voluntary star-motion almost word for word. The Stoics and the Peripatetics disagreed about many things, but they stood together against Epicurus on the divinity of the heavens. Aristotle supplied many of their arguments.

The Peripatetic School in Epicurus’s Time

While Epicurus taught, Aristotle’s school was led first by Theophrastus (head from 322 to about 287 BC) and then by Strato of Lampsacus. The Epicureans engaged both.

Theophrastus. Epicurus wrote a work Against Theophrastus in at least two books. Plutarch quotes from its second book Epicurus’s argument that colours are not intrinsic to bodies but “a result of certain arrangements and positions relative to the eye” (Usener 29–30). Epicurus’s student Leontion also wrote a book against Theophrastus, which so offended Cicero’s Academic spokesman that he called it an example of the licence of the Garden (ND I.93).
Praxiphanes. The chronicler Apollodorus claimed that Epicurus studied under Praxiphanes, a Peripatetic, but “Epicurus himself denies this in his letter to Eurylochus, and says he was his own teacher” (DL X.13).
Strato. Strato abandoned much of Aristotle’s theology and explained nature without a governing god. On one point of physics the later commentator Simplicius groups him with Epicurus: both held, against Aristotle, that every body has weight and that light things rise only because heavier things push them up (Usener 276).

Diogenes of Oinoanda Names Aristotle Among the Doubters

The great Epicurean inscription set up at Oinoanda in the second century AD names Aristotle directly. After attacking those who discard the study of nature by claiming “that things are inapprehensible,” Diogenes continues:

“Now Aristotle and those who hold the same Peripatetic views as Aristotle say that nothing is scientifically knowable, because things are continually in flux and, on account of the rapidity of the flux, evade our apprehension. We on the other hand acknowledge their flux, but not its being so rapid that the nature of each thing [is] at no time apprehensible by sense-perception.” (Diogenes of Oinoanda, Fragment 5, tr. M. F. Smith)

This may seem a surprising charge against the man who wrote the Posterior Analytics. But it makes sense once we see what Aristotle meant by “scientific knowledge.” As the section on the Canon below will show, Aristotle held that the senses grasp only changing particulars, and that knowledge in the strict sense is of what cannot be otherwise. The world of the senses, for Aristotle, is not itself the object of science. Diogenes’s answer is the Epicurean one: things change, but the senses still grasp their nature.

The Later Commentators Preserve the Epicurean Replies

The Greek commentators on Aristotle, writing many centuries later, preserve valuable evidence that Epicurus answered Aristotle point by point. Two examples, both from Simplicius’s commentary on the Physics, Book VI:

Aristotle had argued that if magnitudes were made of partless units, a moving body could never be in the act of moving over a partless unit, only have moved over it. Simplicius reports that “despite his having formulated it and produced his solution, the Epicureans, who came along later, said that this is precisely how motion does occur” (Usener 278).
Aristotle had argued that if there were indivisible distances, quicker and slower bodies would have to cross them in the same time. Simplicius reports: “And that is why the Epicureans too think all bodies move at equal speed through indivisible distances, so that they can avoid having their atomic quantities be divided” (Usener 277).

In both cases Epicurus did not back away from the consequence that Aristotle thought was absurd. He accepted it and built it into his physics. Modern scholars, especially David Furley in Two Studies in the Greek Atomists (1967), have shown how much of Epicurus’s doctrine of minimum parts and of atomic motion was shaped as a reply to Aristotle’s Physics. The Italian scholar Ettore Bignone argued in L’Aristotele perduto e la formazione filosofica di Epicuro (1936) that the young Epicurus also wrote against Aristotle’s early published works, such as On Philosophy, which are now lost. Velleius’s criticism of the third book of On Philosophy, quoted above, is a clear surviving trace of that debate.

The Myth of the “Empiricist” Aristotle

Before turning to the doctrines, we have to clear away a common misunderstanding. Readers who come to Epicurus from a modern education often think of Aristotle as the scientist of antiquity, the man who studied animals and plants and trusted his eyes, in contrast to Plato with his eternal Forms. On that view, Aristotle and Epicurus look like two members of the same team. The ancients did not see it that way, and neither should we.

The ancients put Aristotle with Plato. Cicero has the spokesman of the Old Academy, Varro, say that through Plato “a system of philosophy was established which was one and identical, though under two names; the system namely of the Academics and Peripatetics. For these two schools agreed in reality, and differed only in name” (Cicero, Academic Questions I.17). Sextus Empiricus names Aristotle first among the Dogmatists, the philosophers who “believe they have discovered” the truth (Outlines I.3). He reports that “Aristotle and Theophrastus and the Peripatetics in general,” because they divide things into the sensible and the intelligible, “admit a twofold criterion, sense of things sensible and intellect of things intelligible,” and that intellect is “first in potency” (Against the Logicians I.217–218). And in his list of the main positions on the reliability of the senses, Sextus sets “the Stoics and Peripatetics,” who “have abolished some and established others,” against “Epicurus and Protagoras,” who “have established all” (Against the Logicians I.369). In every ancient line-up, Aristotle stands on the other side from Epicurus.

Aristotle kept the essentials of Plato’s view of the world. Aristotle did reject Plato’s theory that the Forms exist apart from things, and he said so sharply. In the Metaphysics he writes that “to say that they are patterns and the other things share in them is to use empty words and poetical metaphors” (I.9). He begins his attack on the Form of the Good in the Nicomachean Ethics by explaining that although the Forms “have been introduced by friends of our own,” “piety requires us to honour truth above our friends” (I.6). But he kept the conviction that lies behind the theory: that what is truly knowable and truly real is form, not matter; the universal, not the particular; the unchanging, not the changing. For Aristotle, the “form” of a thing is its essence, the “what it is” that a definition states, and this form is the source of its activity and its goal. Form, not atoms and void, is what explains the world. The highest being of all is pure form without any matter: a god who is nothing but thought thinking itself. Part of the human soul shares in this divine nature and is “immortal and eternal.” This is not a rejection of Plato’s “true world.” It is that world brought down into things and given a new name.

Aristotle’s science serves his theology. Aristotle observed animals carefully, and much of his biology is useful. But his physics and astronomy were built to support conclusions that no observation could establish. The heavens must be made of an eternal fifth element because circular motion must belong to a divine body. There must be one world and not many. There can be no void, because motion through a void would have no natural place to end. The first mover must be “without parts and without magnitude.” Over and over, Aristotle argues from what is fitting, perfect, or prior “by nature,” and the answers come out as the theology of the Academy required.

For these reasons Aristotle is best viewed as within the Platonist tradition and among those that adulterate the philosophy of Epicurus. Through the medieval church his system also became the philosophical backbone of supernatural religion, and his ethics of virtue has become a favorite of modern humanism.

The Canon: How Aristotle Says We Know

Praise of the Senses That Stops Short

Aristotle’s Metaphysics opens with a sentence Epicureans can applaud: “All men by nature desire to know. An indication of this is the delight we take in our senses; for even apart from their usefulness they are loved for themselves; and above all others the sense of sight.” In On the Soul he goes further. “Perception of the objects of the special senses is true, or subject to the minimum of error,” he says, and again: “sensations are always true, but imaginings prove for the most part false.” On a first reading this sounds close to Epicurus, who held that “all sensations are true” and that error lies in the opinion we add to them (DL X.31–32; DL X.50–51).

The resemblance is real but shallow. For Aristotle, the senses report only particulars: this white thing, this sound, here and now. They do not reach what he considers knowledge. In the Posterior Analytics he defines knowledge in the strict sense, which the Oxford translators call “scientific knowledge,” as knowing “the cause on which the fact depends, as the cause of that fact and of no other, and, further, that the fact could not be other than it is.” It follows that “the proper object of unqualified scientific knowledge is something which cannot be other than it is.” And Aristotle draws the consequence without hesitation:

“Scientific knowledge is not possible through the act of perception. … Seeing, therefore, that demonstrations are commensurately universal and universals imperceptible, we clearly cannot obtain scientific knowledge by the act of perception: nay, it is obvious that even if it were possible to perceive that a triangle has its angles equal to two right angles, we should still be looking for a demonstration.”

This is the hinge on which the two philosophies turn. For Epicurus, the senses are the first and indispensable standard of truth, and nothing can overrule them: “nor can one sensation refute another,” and “nor again can reason, for all reason is dependent upon sensations” (DL X.32). For Aristotle, the senses are the starting point, but knowledge in the proper sense lives somewhere else: in demonstration from necessary first principles, about objects that “cannot be other than they are.”

Demonstration and the Higher Faculty

How then are the first principles of demonstration known? Aristotle’s answer comes at the end of the Posterior Analytics, and it contains both a close approach to Epicurus and a sharp departure from him.

The approach is his account of how general notions arise. “So out of sense-perception comes to be what we call memory, and out of frequently repeated memories of the same thing develops experience; for a number of memories constitute a single experience.” From experience comes “the universal now stabilized in its entirety within the soul.” Aristotle compares the process to “a rout in battle stopped by first one man making a stand and then another, until the original formation has been restored.” An Epicurean will recognize something like his own account of the preconception, which Diogenes Laertius describes as “a recollection of what has often been presented from without, as for instance ‘Such and such a thing is a man’” (DL X.33).

The departure is where Aristotle ends up. The first principles, he says, are grasped by a faculty that is “truer than scientific knowledge” itself:

“…since except intuition nothing can be truer than scientific knowledge, it will be intuition that apprehends the primary premisses…”

The word translated “intuition” is nous, mind or intellect. In On the Soul Aristotle tells us what this intellect is. The intellect that “makes all things” is “separable and impassive and unmixed, being in its essential nature an activity,” and “this, its essential nature, alone is immortal and eternal.” So the foundations of Aristotle’s science rest, in the end, on a faculty that he describes as divine, separable from the body and deathless. Sextus Empiricus summed it up well: for the Peripatetics, sense comes first in order, but intellect is “first in potency” (Against the Logicians I.218).

Epicurus had no place for any such faculty. For him, the preconceptions are themselves formed from sensations and are tested against them. Reason works with what the senses supply and is always “dependent upon sensations.” There is no higher court, and no part of the mind that touches truths the senses could never confirm. The Epicurean canon has three standards, all of them natural and all of them shared with the animals in some degree: the sensations, the preconceptions, and the feelings of pleasure and pain (DL X.31). Aristotle’s canon has a fourth, and it is the one he trusts most.

The Atomists’ “Mistake,” According to Aristotle

Aristotle thought he knew exactly where the atomists went wrong in their theory of knowledge. Discussing those who say that contradictory appearances are all true, he writes that this is “why Democritus, at any rate, says that either there is no truth or to us at least it is not evident. And in general it is because these thinkers suppose knowledge to be sensation, and this to be a physical alteration, that they say that what appears to our senses must be true.”

The charge is revealing. Aristotle assumes that if knowledge rests on sensation, and sensation is a bodily process, then truth is either impossible or relative. Democritus himself drifted toward that conclusion, which is one of the places where Epicurus corrected him. Epicurus kept the atomist account of sensation as a physical process and refused the skeptical conclusion. Sensations are true precisely because they are caused by real things acting on our bodies: “the visions of the insane and those in dreams are true, for they cause movement, and that which does not exist cannot cause movement” (DL X.32). Truth comes from the contact between real bodies, not from a separable intellect. Aristotle’s dilemma, either a divine intellect or no knowledge at all, is the false choice Epicurus refused.

Logic, Definitions and Dialectic

Aristotle invented formal logic. His Prior Analytics is the first systematic account of the syllogism, and his Topics is a handbook for winning arguments in dialectical debate. The Posterior Analytics insists that real knowledge is gained “by demonstration,” meaning “a syllogism productive of scientific knowledge.” Definitions, divisions into genus and species, and chains of syllogisms were for Aristotle the tools of science.

The Epicureans treated this whole apparatus with suspicion. “Logic they reject as misleading,” reports Diogenes Laertius. “For they say it is sufficient for physicists to be guided by what things say of themselves” (DL X.31). Epicurus told his students not to begin with definitions but with the plain meaning of words: “it is essential that the first mental image associated with each word should be regarded, and that there should be no need of explanation” (DL X.38). Cicero complained that Epicurus “does away with the process of definition; he has nothing to teach about subdivision or partition; he lays down no method for constructing and shaping an argument” (Cicero, On Ends I.22, tr. Reid). The complaint was accurate, and it describes a choice Epicurus made on purpose. Words take their meaning from the things we have perceived, not from definitions built up by division. An argument that runs off from what can be perceived, however neat its form, proves nothing about the world.

This difference has practical consequences. Aristotle’s science aims at the single necessary explanation. Epicurus distinguished two kinds of question. Where only one explanation agrees with the phenomena, as with the doctrine that “the universe consists of bodies and the intangible,” we must hold to it. But many things, especially in the heavens, “admit of more than one cause of coming into being and more than one account of their nature which harmonizes with our sensations” (DL X.86). To insist on one explanation there is to fall back “on the useless course of thinking that things could only happen in one way” (DL X.97). Much of Aristotle’s astronomy is a demonstration that things in the heavens can happen in only one way, and that this way requires a god.

Truth About the Future

One logical question divided the schools sharply. Is every statement about the future already true or false? Aristotle took it up in a famous chapter of On Interpretation (Chapter 9, 18a28–19b4), using the example of a sea-fight that may or may not take place tomorrow. He held to the law of contradiction as “the most certain of all” principles. But he saw that if one of the two statements, “there will be a sea-fight tomorrow” and “there will not be a sea-fight tomorrow,” were already true today, then the future would already be fixed, and there would be no point in deliberating about anything.

He did reach an answer, though scholars still argue over exactly what it means. The whole statement “either there will or there will not be a sea-fight tomorrow” is necessarily true, but neither half of it is yet true or false. In E. M. Edghill’s Oxford translation (Vol. I, 1928): “A sea-fight must either take place to-morrow or not, but it is not necessary that it should take place to-morrow, neither is it necessary that it should not take place, yet it is necessary that it either should or should not take place to-morrow.” Of the two statements, “we cannot say determinately that this or that is false, but must leave the alternative undecided. One may indeed be more likely to be true than the other, but it cannot be either actually true or actually false” (19a30–19b4). So Aristotle kept the law of contradiction for the statement as a whole and gave up, for the future only, the rule that each statement must already be either true or false.

Epicurus came to the same problem from the side of fate. If every statement about the future were already true, then the future would already be fixed, and the Stoic doctrine of fate would follow. Rather than accept that, Epicurus denied that every proposition about future contingent events is true or false now. Cicero reports with disgust that the Epicureans “say that propositions of this sort are neither true nor false” (Cicero, On Fate 37). Cicero adds that when the Epicureans were “ashamed of that,” they said instead that the whole disjunction is true “but that the statements contained in the propositions are neither of them true” (the same passage). That is Aristotle’s own answer. On this one point Epicurus and Aristotle stood together against the Stoics, who held that every statement about the future is already true or false and so made fate inescapable. Here again Epicurus preferred the evidence of experience, that our choices are real, over the claims of formal logic. He did not let a rule of logic overrule what we perceive about ourselves.

Summary: Two Different Canons

Question	Aristotle	Epicurus
Are the senses true?	Mostly, about their special objects; knowledge is not perception	All sensations are true; error is in the opinion added
What is knowledge of?	The universal and necessary, what “cannot be other than it is”	The real nature of things, including changing particulars
How are first principles known?	By intellect (nous), separable and immortal	By preconceptions formed from sensation and checked against it
What is the role of logic?	Demonstration by syllogism is the form of science	Formal logic is unnecessary and misleading for the student of nature
How many explanations?	The single necessary one	One where only one fits the evidence; several where several do
Is the future already true or false?	Troubled, but holds to the law of contradiction	Statements about future chance events are neither true nor false now

Physics: Aristotle’s Universe Against Epicurus’s

Epicurus summed up the nature of things in a few propositions. Nothing comes from nothing, and nothing passes away into nothing. The universe has always been as it is now and always will be. It consists of bodies and void. The bodies are either compounds or the indivisible atoms of which compounds are made. The universe is infinite, both in the number of its atoms and in the extent of its void, and it contains innumerable worlds, some like ours and some unlike it (DL X.38–45, X.39, X.41). Aristotle denied every one of these propositions except the first. His physics is, in effect, a point-by-point rival to the physics of the atomists, and Epicurus’s physics is in large part a reply to Aristotle.

One Finite World, Not Infinite Worlds

For Aristotle the universe and the world are the same thing: a single sphere with the earth at its center and the heaven of fixed stars at its edge. Beyond that edge there is nothing at all. “It is clear then that there is neither place, nor void, nor time, outside the heaven.” On the Heavens devotes a series of chapters to proving that no body can be infinite (I.5–7) and then turns, in Aristotle’s words, to show “why there cannot be more than one heaven.” Chapter 9 announces that “we must show not only that the heaven is one, but also that more than one heaven is impossible.”

What lies “beyond” the outermost heaven, if not body, place or time? Aristotle answers in the language of theology. The beings there “continue through their entire duration unalterable and unmodified, living the best and most self-sufficient of lives.”

Epicurus answered: “the universe is boundless. For that which is bounded has an extreme point: and the extreme point is seen against something else” (Letter to Herodotus, DL X.41). Since the atoms are infinite in number, they cannot all have been used up in one world, or in any limited number of worlds. “There are infinite worlds both like and unlike this world of ours” (DL X.45). Lucretius put the argument in a famous picture: wherever you set the boundary of the universe, a man standing there could throw a spear beyond it (Lucretius I.968–983). For Epicurus, life is not a privilege of one central world; “in all worlds there are living creatures and plants and other things we see in this world” (DL X.74).

No Void, and the Argument Epicurus Turned Around

Aristotle rejected the void outright. “The void is thought to be place with nothing in it,” he writes, and he spends four chapters of the Physics (IV.6–9) arguing that there is no such thing. One of his arguments is especially important. If there were a void, he says, a moving body would have no reason to stop: “no one could say why a thing once set in motion should stop anywhere; for why should it stop here rather than here?” And since speed depends on the resistance of the medium, bodies moving through a void, which offers no resistance, would all move at the same speed: “Therefore all will possess equal velocity. But this is impossible.”

Epicurus accepted both of the “impossible” consequences and made them part of his physics. The atoms do move forever until something stops them, and they do all move at the same speed through the void: “the atoms must move with equal speed, when they are borne onwards through the void, nothing colliding with them. For neither will the heavy move more quickly than the small and light” (DL X.61). What Aristotle offered as a reduction to absurdity, Epicurus treated as a discovery. Epicurus was right. Galileo later showed that heavy and light bodies fall at the same rate when the resistance of the air is removed, and Newton’s first law states that a body in motion continues in motion unless something acts on it. On both points the atomists, not Aristotle, had grasped the truth.

As for the void itself, Epicurus’s argument was simple: “if there were not that which we term void and place and intangible existence, bodies would have nowhere to exist and nothing through which to move, as they are seen to move” (DL X.40). Motion is a fact of perception. Void follows from it.

Against the Atoms

Aristotle rejected the atoms on several grounds, which he set out in On the Heavens, On Generation and Corruption and the Physics. He held that “a view which asserts atomic bodies must needs come into conflict with the mathematical sciences,” because geometry treats every magnitude as divisible without end. In Physics VI he argued that nothing continuous can be made of indivisible parts, because indivisibles could not touch one another part to part, and that indivisible distances would require indivisible movements and equal speeds for all bodies.

Yet Aristotle took the atomists more seriously than he took most of his predecessors. In a passage of On Generation and Corruption he praises Democritus’s method over the method of his own teacher’s school:

“those who dwell in intimate association with nature and its phenomena grow more and more able to formulate, as the foundations of their theories, principles such as to admit of a wide and coherent development: while those whom devotion to abstract discussions has rendered unobservant of the facts are too ready to dogmatize on the basis of a few observations.” And: “whereas the Platonists argue that there must be atomic magnitudes ‘because otherwise “The Triangle” will be more than one’, Democritus would appear to have been convinced by arguments appropriate to the subject, i.e. drawn from the science of nature.”

Later in the same book he concedes that “Leucippus, however, thought he had a theory which harmonized with sense-perception and would not abolish either coming-to-be and passing-away or motion and the multiplicity of things.” These are valuable ancient testimonies to the scientific seriousness of the atomists, and they come from their most formidable opponent. They should not be mistaken for agreement. Aristotle praises the atomists’ method in order to reject their conclusions.

Epicurus’s answer to Aristotle’s mathematical objections was his doctrine of minimum parts. An atom is indivisible in fact, but it has extension, and it is made up of the smallest units of magnitude that can exist. These minimum parts are not points. They are the units by which sizes are measured. “We must not suppose that in a limited body there can be infinite parts or parts of every degree of smallness” (DL X.56). Simplicius, as quoted above, reports that the Epicureans accepted the consequences Aristotle had drawn about motion over indivisible distances (Usener 277–278). Aristotle’s argument shaped the details of Epicurean atomism. It did not overturn it.

Natural Places, Lightness and the Fifth Element

In Aristotle’s universe every simple body has a natural place and a natural motion. Earth moves down toward the center, fire moves up toward the edge, and air and water lie between. Fire is “light” in an absolute sense, not merely less heavy than earth. Epicurus rejected this. All atoms have weight, and things that seem light rise only because heavier things press beneath them (Lucretius II.184–215). As we have seen, Simplicius groups Strato and Epicurus together as holding that “every object possessed weight” (Usener 276).

The heavens, for Aristotle, are made of a fifth element unlike the four elements below. It moves naturally in a circle, and so, he argues, it has no contrary and can neither come to be nor perish. This “primary body” is “eternal and not subject to increase or diminution, but unaging and unalterable and unmodified.” Then Aristotle tells us why he is so confident:

“For all men have some conception of the nature of the gods, and all who believe in the existence of gods at all, whether barbarian or Greek, agree in allotting the highest place to the deity, surely because they suppose that immortal is linked with immortal and regard any other supposition as inconceivable. If then there is, as there certainly is, anything divine, what we have just said about the primary bodily substance was well said.”

Here the theology drives the physics. The heavens must be eternal because the gods live there, and the gods must live there because that is what “all men” believe. Epicurus agreed that there are gods and that men have a true preconception of them as immortal and blessed. But he denied that the gods have anything to do with the heavens. The heavenly bodies “are but fire agglomerated in a mass” (DL X.77), and they come to be and pass away like everything else in a world.

Does Motion Need a Mover?

Behind the dispute over heavy and light lies a larger question, and it is one that readers of Epicurus still ask. Can the atoms move on their own? Or must something outside them push or pull them, as Aristotle held?

Aristotle’s answer is that nothing moves itself. Book VII of the Physics opens with the rule: “Everything that is in motion must be moved by something.” In Book VIII he applies it even to the natural motion of falling stones and rising fire. A heavy body does not move itself, he says. It “contains within itself the source of motion—not of moving something or of causing motion, but of suffering it.” What really moves it is whatever first made it heavy, or whatever removed the thing that was holding it back. His conclusion is that “all things that are in motion must be moved by something” (VIII.4). From this rule the rest of Book VIII builds its chain of movers, which must end in a first mover that is itself unmoved (see “The Unmoved Mover” below).

Aristotle also saw that the atomists did not accept his rule, and he complained of it more than once. Leucippus and Democritus, “who say that the primary bodies are in perpetual movement in the void or infinite,” should be asked what kind of motion is natural to them (On the Heavens III.2). In the Metaphysics he says of Leucippus and Plato that “they say there is always movement. But why and what this movement is they do not say,” and he adds: “Now nothing is moved at random, but there must always be something present to move it” (XII.6).

Epicurus answered the question the atomists had left open, and his answer is the opposite of Aristotle’s. Motion is not given to the atoms from outside. It belongs to them by their own nature. “The atoms move continuously for all time,” he writes, and “these motions have no beginning, since the atoms and the void are the cause” (DL X.43–44). Democritus had given the atoms only size and shape. Epicurus added weight, and the reason he gave was motion: “it is necessary, he argues, that bodies be moved by the blow of their weights, for otherwise they would not move” (Usener 275). Lucretius says the same: the first-beginnings “move on either by their own weight or sometimes by the blow of another” (Lucretius II.80–85, tr. Bailey). Weight is not a push from somewhere else. It is a property of every atom, like its size and shape, and it is the atom’s own cause of motion. Through the void, where nothing stands in the way, every atom moves “with equal speed,” the heavy no faster than the light (DL X.61).

The swerve is a motion of the same kind. According to Lucretius, atoms falling through the void by their own weight “at times quite undetermined and at undetermined spots… push a little from their path” (II.216–220). Nothing outside the atom causes the swerve. That is just why Epicurus needed it. Weight and blows alone would make every motion the necessary result of earlier motions, and the human mind would be “constrained like a conquered thing.” So, Lucretius argues, “in the seeds too you must needs allow likewise that there is another cause of motion besides blows and weights, whence comes this power born in us, since we see that nothing can come to pass from nothing… this is brought about by the tiny swerve of the first-beginnings in no determined direction of place and at no determined time” (II.284–293, tr. Bailey).

Epicurus’s opponents said that a swerve with no outside cause was a motion with no cause at all. Cicero made the charge in On Fate: Epicurus “is compelled to admit, if not by his words, by the facts themselves,” that the swerve comes about without a cause (Usener 281). But in the same book Cicero reports how the Academic Carneades thought the Epicureans should have answered. “Without cause” means “without an external and antecedent cause,” not “without a cause of some kind.” The right way to put it is “that it is the nature of the atom itself to be kept in motion by weight and gravity, and that its nature is itself the cause of its travelling in this manner” (Cicero, On Fate 24–25). That is the Epicurean position. The atom’s motion has a cause, and the cause is the atom itself.

Epicurus’s view contradicts Aristotle’s argument for a first mover. Aristotle and Epicurus agreed that motion never began and never ends. But Aristotle’s chain of movers depends on the rule that nothing moves itself, and Epicurus denied that rule at the level of the atoms. If every atom carries the cause of its own motion, then eternal motion needs no eternal mover. Nothing has to start it, keep it going or steer it. This is one more reason why the Epicurean gods have nothing to do with running the world, a point taken up again under “The Unmoved Mover” below.

Living, Divine Stars

Aristotle did not stop at making the heavens eternal. He made the stars alive. Faced with puzzles about their motions, he writes: “We may object that we have been thinking of the stars as mere bodies, and as units with a serial order indeed but entirely inanimate; but should rather conceive them as enjoying life and action.” In his lost dialogues he argued that their motion is voluntary, as we have seen from Cicero’s Stoic speaker, and in the Metaphysics he assigns to each heavenly sphere its own unmoved mover, so that the gods of the heavens number fifty-five or forty-seven (Metaphysics XII.8).

Epicurus rejected the whole conception, and he explained why it mattered. The belief that the heavenly bodies are blessed beings who move by their own will, or that a god directs them, is the source of “the principal disturbance in the minds of men” (DL X.81). It leads men to fear the heavens and to see in thunder, eclipses and comets the signs of divine anger. “Do not let the divine nature be introduced at any point into these considerations,” he wrote to Pythocles, “but let it be preserved free from burdensome duties and in entire blessedness” (DL X.97).

Chance, Necessity and Purpose in Nature

One of the most important differences between Aristotle and Epicurus in physics concerns purpose. Aristotle’s Physics II is the classic statement of the view that nature acts for ends. He begins by attacking those who explain the world by chance, and among them the atomists:

“There are some too who ascribe this heavenly sphere and all the worlds to spontaneity. They say that the vortex arose spontaneously, i.e. the motion that separated and arranged in its present order all that exists. This statement might well cause surprise.”

He then states the rival view forcefully, and Epicureans should read the passage closely, because it is an ancient forerunner of the theory of natural selection:

“A difficulty presents itself: why should not nature work, not for the sake of something, nor because it is better so, but just as the sky rains, not in order to make the corn grow, but of necessity? … Wherever then all the parts came about just what they would have been if they had come to be for an end, such things survived, being organized spontaneously in a fitting way; whereas those which grew otherwise perished and continue to perish, as Empedocles says his ‘man-faced ox-progeny’ did.”

And Aristotle rejects it: “Yet it is impossible that this should be the true view.” His reason is that useful arrangements occur “invariably or normally,” while chance produces only what is occasional. “It is plain then that nature is a cause, a cause that operates for a purpose.” In On the Heavens he gives the principle its shortest form: “But God and nature create nothing that has not its use.” In On the Soul: “nature makes nothing in vain.”

The Epicurean answer is the one Aristotle rejected. Lucretius tells how the earth in its youth produced many creatures that could not feed, defend themselves or reproduce, and how they died out, so that the kinds we see today are those that could survive (Lucretius V.837–877). The appearance of design is the result of this weeding out, not of planning. And Lucretius denies Aristotle’s principle at its root: “nothing at all was born in the body that we might be able to use it, but what is born creates its own use” (Lucretius IV.833–835, tr. Bailey). Eyes were not made for seeing. Seeing came about because there were eyes.

Aristotle’s argument that what happens “invariably or normally” cannot be the result of chance does not touch the Epicurean view. Epicurus never said that living things arise by pure chance each time. He said that the regularities of nature come from the fixed natures of the atoms and from the weeding out of forms that could not survive, so that the same seeds always produce the same kinds. The order of nature needs no purpose behind it, and no mind to supply one.

The Unmoved Mover

Aristotle’s physics ends in theology. The eighth book of the Physics argues that motion is eternal, that every motion requires a mover, and that the chain of movers must end in a first mover that “must be unmoved” and “without parts and without magnitude.” The twelfth book of the Metaphysics tells us what this first mover is. It moves the heavens not by pushing them but as an object of desire and love moves those who desire it. It is pure activity, and its activity is thought:

“On such a principle, then, depend the heavens and the world of nature. And it is a life such as the best which we enjoy, and enjoy for but a short time (for it is ever in this state, which we cannot be), since its actuality is also pleasure.”

What does this god think about? Only the best thing, which is itself: “its thinking is a thinking on thinking.”

It is worth noticing that Aristotle, too, calls the life of his god a life of pleasure. On this one point he and Epicurus agree: the happiest being enjoys its existence. Everything else about Aristotle’s god is the opposite of Epicurus’s. Aristotle’s god has no body, no senses and no friends. It is the cause on which “the heavens and the world of nature” depend. And Aristotle draws from it a political lesson. The universe, he says, is ordered toward its good “as an army does; for its good is found both in its order and in its leader, and more in the latter.” He closes the book by quoting Homer: “‘The rule of many is not good; one ruler let there be.’” The ruler of the universe becomes the model for the ruler of men.

Epicurus drew no such lesson, and the difference shows again how far apart the two men stood. Aristotle reasons from the order of the heavens down to the order of the state: because the universe has one ruler, the rule of one is best. Epicurus had no ruler of the universe from which to reason, and he never said that the rule of one is better than the rule of many, or the reverse. He judged every form of government by a single test, the security it gives: “To secure protection from men anything is a natural good, by which you may be able to attain this end” (Principal Doctrine 6). The manuscripts of this saying add the words “rule and kingship” as examples of such means. Editors disagree about whether Epicurus wrote them, and Bailey’s commentary sets out the dispute. But even if he did, kingship is good only as a means to safety, never as the best order of things.

Lucretius gives the Epicurean history of government, and it favors no form for its own sake. The first kings built cities “to be for themselves a strong-hold and a refuge.” In time the kings were put to death, and “things would pass to the utmost dregs of disorder, when every man sought for himself the power and the headship.” Then men were taught “to appoint magistrates and establish laws,” and they accepted them because they were “worn out with leading a life of violence” (Lucretius V.1105–1160, tr. Bailey). The only clear preference Lucretius states is a personal one, not a political one: “it is far better to obey in peace than to long to rule the world with kingly power and to sway kingdoms.” Epicurus himself wrote a book On Kingship (Usener 5–6), but Plutarch complains that the Epicureans wrote “about kingship to make us shun the company of kings” (Usener 8). The wise man, says Diogenes Laertius, “will pay court to a king, if occasion demands” (DL X.121). That is advice for living safely under whatever government one has, not a theory of the best state. The bluntest judgment in the surviving Epicurean texts may be a single sentence from a damaged column of Philodemus’s On Rhetoric: “Rhetors prefer to live in a democracy, the worst form of government” (Book VII, tr. H. M. Hubbell, 1920, p. 339). Even here the point is not that one ruler is better than many. The papyrus is too broken to show whether Philodemus is speaking for himself or reporting another’s view, and the sentence is about the orators, who thrive where crowds decide. For the Epicureans the question of who should rule was never settled by appeal to the heavens. It was settled, case by case, by which arrangement best lets men live in safety.

Epicurus’s gods are the reverse in every respect. They do not move the heavens or govern anything. “The blessed and immortal nature knows no trouble itself, nor causes trouble to any other, so that it is never constrained by anger or favor” (Principal Doctrine 1). Velleius’s objection to Aristotle, quoted above, goes to the heart of the matter: a being that is “always in motion,” or that sustains the motion of the heavens, cannot “enjoy tranquillity and bliss” (ND I.33). A god who must keep the universe turning is a laborer, not a blessed being.

Myths “With a View to the Persuasion of the Multitude”

One passage of the Metaphysics deserves special attention, because in it Aristotle says openly what Epicurus accused the religion of his day of doing. Aristotle explains that the ancients rightly thought the heavenly bodies were gods:

“Our forefathers in the most remote ages have handed down to their posterity a tradition, in the form of a myth, that these bodies are gods, and that the divine encloses the whole of nature. The rest of the tradition has been added later in mythical form with a view to the persuasion of the multitude and to its legal and utilitarian expediency; they say these gods are in the form of men or like some of the other animals…”

Aristotle thought the stories of gods in human form were tools of social control, added to keep the many in line, while the “true” core of the tradition was that the stars are divine. Epicurus held almost exactly the reverse. The preconception that the gods exist in human-like form and live in blessedness is true, for it comes from “clear vision.” What is false, and what does the damage, is the belief that the gods govern the heavens and the affairs of men and reward and punish. “The statements of the many about the gods are not conceptions derived from sensation, but false suppositions, according to which the greatest misfortunes befall the wicked and the greatest blessings (the good) by the gift of the gods” (DL X.124). Aristotle kept the divine heavens and approved the useful lie. Epicurus rejected both.

The Eternity of the World

On one point Aristotle and Epicurus agreed against Plato. Plato’s Timaeus had described the world as made by a divine craftsman, and Aristotle notes that “Plato alone asserts the creation of time, saying that it had a becoming together with the universe.” Aristotle held that the world never had a beginning, and Epicurus held that the universe never had a beginning. Epicureans should not make too much of this agreement. For Aristotle the eternal world is an eternal order: the same heavens, the same species, the same divine motion, forever. For Epicurus the universe is eternal, but every world within it, including ours, is born and will die (Lucretius V.235–415). Aristotle’s world was not made by a god, but it is everywhere directed toward ends, and its motion depends on a god. The Epicurean arguments against Plato’s creator, and against the Stoic providence that carried the same creationism forward, apply with equal force to Aristotle’s god-governed order.

The Soul

Aristotle defined the soul as the form of a living body: “soul is the first actuality of a natural body having in it the capacity of life.” On this view the soul is not a thing in its own right, as it was for Plato, but the organization and activity of the body. Some modern readers have taken this as a materialist view, close to Epicurus. It is not.

First, Aristotle rejected the atomist account of the soul in detail. In Book I of On the Soul he reports that “Democritus affirms the soul to be a sort of fire or heat. For the “shapes” or atoms are infinite and those which are spherical he declares to be fire and soul,” and he devotes much of the book to refuting this and similar views. For Aristotle the soul is not a body at all. Epicurus answered that “the soul is a body of fine particles distributed throughout the whole structure” (DL X.63).

Second, Aristotle exempted the highest part of the soul from death. As we saw above, the active intellect is “separable and impassive and unmixed,” and “this, its essential nature, alone is immortal and eternal” (On the Soul III.5). Interpreters have argued for two thousand years over what this means, but the words are plain enough, and the Christian scholastics read them as support for the immortality of the soul. Epicurus allowed no exception: “if the whole structure is dissolved, the soul is dispersed and no longer has the same powers nor performs its movements, so that it does not possess sensation either” (DL X.65).

Perception: Forms Without Matter, or Images?

How do we perceive? Aristotle’s answer is that “sense is that which is receptive of sensible forms apart from their matter, as wax receives the imprint of the signet-ring apart from the iron or gold of which it is made.” Nothing material passes from the object to the eye. The medium between them, such as air or water, is changed by the object, and the change is passed along to the sense-organ.

The atomists said that something material does pass: thin films or images that stream off the surfaces of things and enter the eye. Aristotle rejected this. In On Sense and the Sensible he says that to “say with the ancients that colours are emanations, and that the visibility of objects is due to such a cause, is absurd,” and he criticizes Democritus for explaining “seeing as mere mirroring.”

Epicurus defended the images: “there are images like in shape to the solid bodies, far surpassing perceptible things in their subtlety of texture,” which preserve “the respective position and order which they had before in the solid bodies: these images we call idols” (DL X.46). The difference matters for the Canon. On the Epicurean view, the sensation is caused by a real material image of the object, which is why it can be trusted. On Aristotle’s view, what reaches us is a “form” without matter, and the grasp of forms leads, step by step, up to the immaterial intellect.

Dreams Are Not Sent by God

On the subject of dreams Aristotle took a position close to Epicurus’s but not identical. In his short treatise On Prophesying by Dreams, he doubts that dreams come from the gods, for “it is absurd to combine the idea that the sender of such dreams should be God with the fact that those to whom he sends them are not the best and wisest, but merely commonplace persons.” Since animals dream too, “it may be concluded that dreams are not sent by God, nor are they designed for this purpose.” Most prophetic dreams that come true are coincidences, “like that of persons who play at even and odd.”

Even here Aristotle does not quite let go. Dreams “have a divine aspect, however, for Nature [their cause] is divinely planned, though not itself divine.” And he mentions Democritus’s explanation of dreams by “images” and “emanations” only to offer a different one. Epicurus agreed that the gods do not send dreams to warn or reward us. But he gave dreams a more important place: the images of the gods that reach us in sleep are one source of our true preconception of what the gods are like (Lucretius V.1169–1182).

Ethics: Virtue and Contemplation Against Pleasure

Happiness Is the Goal, but What Is Happiness?

Aristotle and Epicurus agreed on the form of the question. Both held that there is a single highest good, desired for its own sake and not for the sake of anything else, and both called it happiness. Aristotle writes that “both the general run of men and people of superior refinement say that it is happiness, and identify living well and doing well with being happy; but with regard to what happiness is they differ.” Epicurus agreed that everything is done for the sake of the blessed life.

They disagreed about what happiness is, and the disagreement could not be sharper. Epicurus: “we call pleasure the beginning and end of the blessed life. For we recognize pleasure as the first good innate in us, and from pleasure we begin every act of choice and avoidance, and to pleasure we return again, using the feeling as the standard by which we judge every good” (DL X.129). Aristotle, after his famous argument from the “function” of man, concludes that “human good turns out to be activity of soul in accordance with virtue, and if there are more than one virtue, in accordance with the best and most complete.”

The whole of Aristotle’s ethics follows from this definition. Virtue is not a means to happiness, as it is for Epicurus. The activity of virtue is happiness. And since the best virtue belongs to the best part of the soul, the best life of all will turn out to be the life of the divine intellect.

”A Life Suitable to Beasts”

Aristotle opens his review of the candidates for happiness with the life of pleasure, and he dismisses it in the language that the enemies of Epicurus would repeat for the next two thousand years:

“To judge from the lives that men lead, most men, and men of the most vulgar type, seem (not without some ground) to identify the good, or happiness, with pleasure; which is the reason why they love the life of enjoyment. For there are, we may say, three prominent types of life—that just mentioned, the political, and thirdly the contemplative life. Now the mass of mankind are evidently quite slavish in their tastes, preferring a life suitable to beasts…”

Notice how the argument works. Aristotle never shows that pleasure is not the good. He identifies pleasure with the tastes of “the mass of mankind,” calls those tastes “slavish,” and moves on. Later in the work he uses the same device. Bodily pleasures cannot be happiness, he says, because “any chance person—even a slave—can enjoy the bodily pleasures no less than the best man; but no one assigns to a slave a share in happiness.” The argument assumes what it sets out to prove: that happiness belongs to “the best man,” defined by his virtue, and not to anyone who simply lives pleasantly.

Epicurus answered this kind of argument in the Letter to Menoeceus. When we say that pleasure is the end, “we do not mean the pleasures of profligates and those that consist in sensuality, as is supposed by some who are either ignorant or disagree with us or do not understand” (DL X.131). Pleasure for Epicurus includes all experience that is not painful: the pleasures of the body, but also friendship, conversation, learning, memory and confident expectation. And the reason we choose it is not that the crowd chooses it, but that nature has given every living creature the feelings of pleasure and pain as its guide.

Eudoxus: The Hedonist Aristotle Could Not Refute

Aristotle knew the case for pleasure well, because it had been made inside Plato’s Academy by the astronomer and mathematician Eudoxus of Cnidus. Aristotle’s report of Eudoxus’s argument is the earliest surviving statement of what Epicureans call the cradle argument:

“Eudoxus thought pleasure was the good because he saw all things, both rational and irrational, aiming at it, and because in all things that which is the object of choice is what is excellent, and that which is most the object of choice the greatest good … He believed that the same conclusion followed no less plainly from a study of the contrary of pleasure; pain was in itself an object of aversion to all things…”

Aristotle adds a revealing remark: Eudoxus’s “arguments were credited more because of the excellence of his character than for their own sake; he was thought to be remarkably self-controlled, and therefore it was thought that he was not saying what he did say as a friend of pleasure, but that the facts really were so.” In other words, the argument for pleasure was respectable only when it came from a man who did not seem to enjoy himself.

Aristotle could not bring himself to reject Eudoxus’s starting point. In Book I he says that “Eudoxus also seems to have been right in his method of advocating the supremacy of pleasure.” In Book VII he goes further: “the fact that all things, both brutes and men, pursue pleasure is an indication of its being somehow the chief good.” And in Book X, against those who say that what all things aim at is not necessarily good, he replies that they are “talking nonsense. For we say that that which every one thinks really is so.” Yet in the end he refuses the conclusion. Pleasure, he decides, is good, but it is not the good. The best pleasures are those that accompany the best activities, and so the activity, not the pleasure, is what matters.

Epicurus took Eudoxus’s argument and followed it to its conclusion. “Every creature, as soon as it is born, seeks after pleasure and delights therein as in its supreme good, while it recoils from pain as its supreme evil” (Torquatus in Cicero, On Ends I.30, tr. Reid). Sextus Empiricus reports the Epicurean version: the animals, “as soon as they are born, when still unperverted, seek after pleasure and avoid pains” (Outlines III.194). Where Aristotle hesitated, Epicurus did not.

Higher Pleasures, Lower Pleasures, and the Good Man as Measure

Aristotle’s treatment of pleasure in Book X of the Ethics is subtle. He argues—against the Platonists—that pleasure is not a “process” or a “becoming,” but something complete at every moment, like seeing. He writes that “pleasure completes the activity not as the corresponding permanent state does, by its immanence, but as an end which supervenes as the bloom of youth does on those in the flower of their age.”

But Aristotle uses this account to divide pleasures into higher and lower kinds, and to declare that some pleasures are not really pleasures at all. Because each activity has its own pleasure, pleasures differ in worth as the activities do: “The pleasure proper to a worthy activity is good and that proper to an unworthy activity bad.” And who decides which activities, and therefore which pleasures, are worthy? The “good man:”

“But in all such matters that which appears to the good man is thought to be really so. If this is correct, as it seems to be, and virtue and the good man as such are the measure of each thing, those also will be pleasures which appear so to him, and those things pleasant which he enjoys. If the things he finds tiresome seem pleasant to some one, that is nothing surprising; for men may be ruined and spoilt in many ways; but the things are not pleasant, but only pleasant to these people and to people in this condition. Those which are admittedly disgraceful plainly should not be said to be pleasures, except to a perverted taste…”

This passage is the source of a way of speaking that Epicureans must reject: the habit of dividing pleasures into “real” ones and pleasures that are “not really pleasures,” and of handing the judgment to the virtuous man. For Epicurus, the feeling of pleasure is itself a standard of truth, as the senses are. A pleasure is always a pleasure. What can be wrong is not the feeling but the choice: a pleasure may be small, or short, or followed by pains that outweigh it. “No pleasure is a bad thing in itself; but the means which produce some pleasures bring with them disturbances many times greater than the pleasures” (Principal Doctrine 8). Aristotle makes the choice of the virtuous man the measure of pleasure. Epicurus makes pleasure the measure of choice.

Aristotle also gives us the image that has followed Epicurus ever since: “no one would choose to live with the intellect of a child throughout his life, however much he were to be pleased at the things that children are pleased at.” The argument is aimed at a straw man. No Epicurean text says that the pleasures of a child are the greatest available to an adult. The point of the Epicurean classification of desires, and of the “sober reasoning” Epicurus praised (DL X.132), is precisely to find the greatest pleasures available to a mature and informed human being.

Pleasure as Restoration, and the “Painless State”

In Book VII Aristotle reports the views of others in Plato’s school who denied that pleasure is a good at all. One of their arguments was that “A man of practical wisdom pursues what is free from pain, not what is pleasant.” Aristotle himself held that “the processes that restore us to our natural state are only incidentally pleasant,” and that true pleasures “are not processes nor do they all involve process—they are activities and ends.”

These passages matter for Epicureans because so much modern writing about Epicurus is built on them. The Academic view that the wise man seeks freedom from pain rather than pleasure treats painlessness as a higher but neutral state between pleasure and pain. Aristotle’s division between the pleasures of “restoration” and the pleasures of unimpeded activity has become the frame through which many scholars read Epicurus’s distinction between active and stable pleasures, and from there they conclude that Epicurus’s real goal was a quiet, painless “tranquility.” Both frames are foreign to Epicurus. He denied that there is any neutral state: “what was thought by some to be a middle term, the absence of all pain, was not only itself pleasure, but the highest pleasure possible” (Torquatus in Cicero, On Ends I.38, tr. Reid). For Epicurus, freedom from pain is pleasure, and it is reached by living, not by withdrawing from life. Readers who meet the “absence of pain” in Epicurus should remember that the idea of a painless neutral state, preferred by the wise man to pleasure, comes from Plato’s school by way of Aristotle’s report, and not from Epicurus.

Contemplation: “Make Ourselves Immortal”

At the end of the Ethics, Aristotle tells us what the best life really is. If happiness is activity in accordance with the highest virtue, it must be the activity of “the best thing in us,” and that is the intellect. The happiest life is the life of contemplation, the study of eternal and unchanging truths for their own sake. But this life, he admits, is more than human:

“But such a life would be too high for man; for it is not in so far as he is man that he will live so, but in so far as something divine is present in him … But we must not follow those who advise us, being men, to think of human things, and, being mortal, of mortal things, but must, so far as we can, make ourselves immortal, and strain every nerve to live in accordance with the best thing in us…”

The model for this life is the life of the gods. What do the gods do? Not just acts, or brave ones, or generous ones: “Therefore the activity of God, which surpasses all others in blessedness, must be contemplative.” And so the human life most akin to it is the happiest.

This is the heart of the matter. Epicurus also held that the gods are models of the happiest life, and that a wise man can “live like a god among men” (DL X.135). But Epicurus’s gods are living beings who enjoy their existence, and the godlike life is a life of pleasure among friends, not a life of pure thought in imitation of a god without a body. Aristotle tells the mortal to make himself immortal. Epicurus tells him that he is mortal, that this is no cause for grief, and that a mortal life well lived is complete. “Infinite time contains no greater pleasure than limited time, if one measures, by reason, the limits of pleasure” (Principal Doctrine 19).

Death: “The Most Terrible of All Things”

The contrast is sharpest on the subject of death. In his discussion of courage, Aristotle writes:

“Now death is the most terrible of all things; for it is the end, and nothing is thought to be any longer either good or bad for the dead.”

Epicurus begins from exactly the same premise and draws exactly the opposite conclusion. Death is the end, and nothing is good or bad for the dead. Therefore death is nothing to us: “So death, the most terrifying of ills, is nothing to us, since so long as we exist, death is not with us; but when death comes, then we do not exist. It does not then concern either the living or the dead, since for the former it is not, and the latter are no more” (DL X.125).

Aristotle goes further. The better a man is, he says, the more he should dread death: “the more he is possessed of virtue in its entirety and the happier he is, the more he will be pained at the thought of death; for life is best worth living for such a man, and he is knowingly losing the greatest goods, and this is painful.” For Aristotle, courage is the virtue of the man who faces this terror for the sake of what is noble, above all in battle. For Epicurus, the terror itself is a mistake, and the man who understands the nature of death is freed from it.

Aristotle was even unsure whether the dead are beyond harm. He discusses whether a dead man can be affected by the fortunes of his children and descendants, since “both evil and good are thought to exist for a dead man, as much as for one who is alive but not aware of them,” and concludes only that if anything good or bad reaches the dead, “it must be something weak and negligible.” Epicurus would not leave even this much uncertainty: “Death is nothing to us, for that which is dissolved is without sensation; and that which lacks sensation is nothing to us” (Principal Doctrine 2).

External Goods, Fortune, and the Man on the Rack

Aristotle held that the virtuous man needs external goods to be happy: friends, wealth, power, good birth, good children and good looks. “Yet evidently, as we said, it needs the external goods as well,” and “the man who is very ugly in appearance or ill-born or solitary and childless is not very likely to be happy.” Since these goods depend on fortune, the happiness of even the best man is exposed to chance. Aristotle draws the consequence in a sentence that seems aimed directly at the claim, later recorded as Epicurus’s, that the wise man is happy even under torture:

“Those who say that the victim on the rack or the man who falls into great misfortunes is happy if he is good, are, whether they mean to or not, talking nonsense.”

Epicurus held the opposite: “even if the wise man be put on the rack, he is happy,” though, Diogenes Laertius adds, “when he is on the rack, then he will cry out and lament” (DL X.118). He did not deny the pain. He denied that pain, which is either short or bearable, can outweigh the pleasures of memory, friendship and understanding that the wise man carries with him. “In but few things chance hinders a wise man, but the greatest and most important matters, reason has ordained” (Principal Doctrine 16). Epicurus himself proved the point on his last day, when he wrote that the pain of his illness was set against “the joy in my heart at the recollection of my conversations with you” (DL X.22).

Honour and the “Great-Souled” Man

Aristotle’s portrait of the man of “pride” or greatness of soul (Book IV, Chapter 3) describes the ideal citizen of the Greek city: a man who thinks himself worthy of great things and is worthy of them, and whose chief concern is honour. For Aristotle, “honour is the prize of virtue, and it is to the good that it is rendered.”

Epicurus regarded the craving for honour and fame as an empty desire, neither natural nor necessary, because such craving can never be satisfied and depends on the opinions of others. “Some men wished to become famous and conspicuous, thinking that they would thus win for themselves safety from other men” (Principal Doctrine 7). Fame is worth having only to the extent that it actually brings security. This is not a counsel of withdrawal. Epicurus and many of his followers were active in the life of their cities. But the Epicurean judged honour by what it brought him, not as the reward of virtue or the goal of a noble life.

Justice: By Nature or by Agreement?

Aristotle taught that “of political justice part is natural, part legal, natural, that which everywhere has the same force and does not exist by people’s thinking this or that.” Epicurus agreed that justice has a basis in nature, but he located that basis in mutual advantage: “The justice which arises from nature is a pledge of mutual advantage, to restrain men from harming one another, and save them from being harmed” (Principal Doctrine 31). And he denied that justice exists apart from agreements: “Justice never is anything in itself, but in the dealings of men with one another, in any place whatever, and at any time, it is a kind of compact not to harm or be harmed” (Principal Doctrine 33). For Aristotle, the natural part of justice is the same everywhere. For Epicurus, what is just is what is advantageous to those who make the agreement, and it can change as circumstances change (Principal Doctrines 36–38).

Friendship

Aristotle’s books on friendship (VIII and IX) are the parts of his ethics that Epicureans most often admire. “For without friends no one would choose to live, though he had all other goods.” Epicurus would agree: “Of all the things which wisdom acquires to produce the blessedness of the complete life, far the greatest is the possession of friendship” (Principal Doctrine 27).

But the agreement is narrower than it looks. Aristotle divides friendship into three kinds: for utility, for pleasure, and for virtue. The first two are inferior and unstable: “those who love each other for their utility do not love each other for themselves but in virtue of some good which they get from each other. So too with those who love for the sake of pleasure.” Only the third is complete: “Perfect friendship is the friendship of men who are good, and alike in virtue.” Friendship founded on pleasure is, for Aristotle, the friendship of the young, who “live under the guidance of emotion.”

Epicurus rejected this ranking. Friendship begins from need and from the pleasures and help it brings, and it is precisely for the sake of the pleasure and security it provides that the wise man values it so highly. “The same knowledge that makes one confident that nothing dreadful is eternal or long-lasting also recognizes, in the face of these limited evils, the security afforded by friendship” (Principal Doctrine 28). Because a friendship is valued for the good it brings to the friends, the Epicurean will go to great lengths for his friend, and “on occasion he will even die for a friend” (DL X.121). Aristotle’s “perfect” friendship is reserved for men who are good in his sense, and it looks down on the friendships of pleasure. The Epicurean values his friends because of the pleasure and security they bring, and he does not apologize for it.

Law, Compulsion and the Imposed Good

Aristotle’s ethics leads into his politics, and its last chapter shows where it is headed. Arguments, Aristotle says, are not enough to make most men good:

“…for most people obey necessity rather than argument, and punishments rather than the sense of what is noble. This is why some think that legislators ought to stimulate men to virtue and urge them forward by the motive of the noble…”

The state, for Aristotle, exists to make its citizens virtuous, and it may use law and punishment to do so. The good is defined by the virtuous few, and the many must be brought to it by compulsion. This is the pattern that Epicurus resisted, and that later critics of moral absolutism, Nietzsche above all, would recognize in the whole tradition from Plato onward: a “good” defined from above and imposed on others for their own good. Epicurus’s ethics begins instead from the feelings of each living being, and his justice from agreements made for mutual advantage. The Epicurean does not need a legislator to tell him what is good for him. He needs to understand the nature of things, so that his choices are guided by his own pleasure rightly understood.

Choice and Responsibility

On one important point of ethics Aristotle and Epicurus stood together against the Stoics and the determinists. Aristotle devotes the opening chapters of Book III to the voluntary and the involuntary, and argues that virtue and vice are “in our own power,” so that praise and blame are justified. Epicurus agreed that “that which is in our control is subject to no master, and to it are naturally attached praise and blame” (DL X.133). But Epicurus saw a danger that Aristotle did not face directly: if every motion of the atoms were fixed in advance, there would be no room for choice at all. His doctrine of the swerve of the atoms was meant to secure, within atomism, the freedom of choice that Aristotle took for granted. David Furley argued in Two Studies in the Greek Atomists that Epicurus’s account of voluntary action was shaped by Aristotle’s, and that the swerve was not meant to make each choice random but to break the chain of necessity that would otherwise run back before our birth.

Where Aristotle Helps the Epicurean Case

Aristotle is a hostile witness, but like Sextus Empiricus he can be a valuable one. A reader who keeps the fundamental disagreement in view can use his works in several ways.

He preserves the atomists. Much of what we know of Leucippus and Democritus comes from Aristotle’s reports. His summary of their doctrine in the Metaphysics is the classic statement: “Leucippus and his associate Democritus say that the full and the empty are the elements, calling the one being and the other non-being,” and the differences among atoms are “shape and order and position.” His accounts in On Generation and Corruption (I.2, I.8), in the Physics on the void (IV.6–9), and in On the Soul on the atomic soul (I.2) are all essential evidence.
He testifies to the scientific seriousness of the atomists. As we have seen, he says that Democritus argued from “the science of nature” while the Platonists argued from abstractions, and that Leucippus sought a theory that “harmonized with sense-perception.”
He states, in order to reject, an ancient forerunner of natural selection. A clear ancient statement of the argument that living things survive because they happen to be fitted to survive is Aristotle’s own, in Physics II.8. Epicureans can read it there in the form Aristotle thought he had refuted.
He attacks Plato. Aristotle’s criticisms of the separate Forms (Metaphysics I.9, XIII–XIV; Nicomachean Ethics I.6) and of the creation of the world in time (Physics VIII.1) are weapons Epicureans can use against Platonism, so long as they remember that Aristotle’s own system keeps the substance of what he criticizes.
He doubts god-sent dreams. His short treatise On Prophesying by Dreams gives natural explanations for dreams that seem to foretell the future, and says plainly that “dreams are not sent by God.”
He admits the force of the case for pleasure. He grants that “all things, both brutes and men, pursue pleasure,” that this “is an indication of its being somehow the chief good,” and that Eudoxus was “right in his method.” He calls the life of his god a life of pleasure. Each of these concessions is a foothold for the Epicurean argument.

None of this makes Aristotle an ally. Each concession serves an alternative order: forms in place of atoms, purpose in place of selection, a divine mover in place of a natural universe, virtue and contemplation in place of pleasure. The value of his testimony comes from the fact that he was an opponent who understood exactly what he opposed.

Aristotle’s Long Shadow

The Hellenistic Schools

After Strato, the Lyceum declined, and for two centuries Aristotle’s technical works were little read. The Stoics took over much of his logic and many of his arguments for the divinity of the heavens, while rejecting his fifth element and his separable intellect. In the first century BC Antiochus of Ascalon taught that the Academy, the Peripatetics and the Stoics agreed in substance and differed mainly in words, and he built a combined ethics of virtue and “the goods of nature” against Epicurus. Cicero gives this view to Varro in the Academic Questions and to Piso in the fifth book of On Ends. Against all of these combinations the Epicureans stood alone, and they knew it. In the ancient line-ups of schools, Aristotle’s followers sit with the Platonists and the Stoics on one side, and Epicurus on the other.

The Middle Ages

When Aristotle’s works were recovered in the Islamic world and then in the Latin West, they became the framework of one of the most powerful systems of thought Europe had known. Thomas Aquinas made Aristotle’s argument for a first unmoved mover the first of his “Five Ways” of proving the existence of God (Summa Theologiae I, question 2, article 3). Aristotle’s account of the soul as the form of the body, joined to his separable intellect, became the philosophical basis for the doctrine of the immortal soul. His ethics of virtue was fitted to the Christian virtues, and his contemplative life became the model for the contemplation of God. Dante placed Aristotle in Limbo among the virtuous pagans, honoured as the master of those who know, while he placed in burning tombs in the sixth circle of Hell “Epicurus all his followers, / Who with the body mortal make the soul” (Inferno X.14–15, tr. Longfellow).

The pattern was set for centuries. Aristotle was “the Philosopher,” and Epicurus was the name for the pleasure-seeker, the atheist and the denier of the soul. When atomism returned in the seventeenth century with Gassendi, Boyle and Newton, it returned as a challenge to Aristotelian physics, and the new science won its victories against Aristotle’s natural places, his denial of the void, his single closed universe and his purposive nature, in nearly every case on ground that Epicurus had held first.

The Modern Revival of Aristotle’s Ethics

In ethics Aristotle’s influence is again strong. Since the mid-twentieth century, “virtue ethics” has become one of the leading schools of moral philosophy, and many writers who reject Aristotle’s god and his immortal intellect embrace his account of the good life as the exercise of virtue. The Greek word for happiness is now routinely translated as “flourishing,” and the virtues are presented as the constituents of a flourishing life rather than as means to pleasure. This modern Aristotelianism is one of the main sources of the humanist misreading of Epicurus, in which the Epicurean pursuit of pleasure is reshaped into a quiet life of moderation, character and self-restraint.

Epicureans should recognize this move when they see it. When a modern author describes Epicurus’s goal as “flourishing,” treats the virtues as the content of happiness, or ranks pleasures as “higher” and “lower,” he is reading Epicurus through Aristotle. When a scholar explains Epicurus’s distinction between active and stable pleasures in terms of Aristotle’s distinction between pleasure as “activity” and pleasure as “restoration,” and concludes that Epicurus’s real goal was a painless calm, he is reading Epicurus through Aristotle’s report of Plato’s school. The Epicurean texts say something simpler and bolder: pleasure is the goal, the feelings are the standard, virtue is the means, and the full and active life of pleasure among friends is the best life a mortal can live.

The Surviving Works

Aristotle’s surviving works are lecture-treatises, written for use within his school. The polished dialogues he published for a wider audience, which Cicero praised for their “golden stream of eloquence,” are lost except for fragments. Since the edition of Immanuel Bekker (Berlin, 1831), every passage of Aristotle has been cited by Bekker’s page, column (a or b) and line, so that Physics 198b16 means page 198, column b, line 16 of Bekker’s Greek text. The translations on this site are marked with these references, and every one of them is a link target.

The table below lists the works traditionally included in the Aristotelian corpus, with the Oxford volume in which each appears. The works with full translations on this site are linked. The others can be read in the Oxford volumes at the Internet Archive.

Work	Bekker pages	On this site	Oxford translation
*Logic (the Organon)*
Categories, On Interpretation	1a–24b		Vol. I (1928)
Prior Analytics	24a–70b		Vol. I
Posterior Analytics	71a–100b	Full text	Vol. I
Topics, Sophistical Refutations	100a–184b		Vol. I
Nature
Physics	184a–267b	Full text	Vol. II (1930)
On the Heavens	268a–313b	Full text	Vol. II
On Generation and Corruption	314a–338b	Full text	Vol. II
Meteorology	338a–390b		Vol. III (1931)
On the Soul	402a–435b	Full text (Hicks)	Vol. III
Short natural treatises (Parva Naturalia)	436a–480b	Five treatises	Vol. III
History of Animals	486a–638b		Vol. IV (1910)
Parts, Movement, Progression and Generation of Animals	639a–789b		Vol. V (1912)
Minor works, many not by Aristotle (Opuscula)	various		Vol. VI (1913)
Problems (mostly by later Peripatetics)	859a–967b		Vol. VII (1927)
First Philosophy
Metaphysics	980a–1093b	Full text	Vol. VIII (1928)
Ethics and Politics
Nicomachean Ethics	1094a–1181b	Full text	Vol. IX (1925)
Magna Moralia, Eudemian Ethics, On Virtues and Vices	1181a–1251b		Vol. IX
Politics, Economics, Constitution of Athens	1252a–1353b		Vol. X (1921)
Rhetoric and Poetry
Rhetoric, Rhetoric to Alexander, Poetics	1354a–1462b		Vol. XI (1924)

Several of the works not on this site touch Epicurean concerns. On Interpretation Chapter 9 is the famous discussion of statements about the future. The Meteorology gives Aristotle’s explanations of thunder, lightning, comets and earthquakes, which Epicurus answered with the multiple explanations of the Letter to Pythocles. The Parts of Animals opens with Aristotle’s defence of the study of animals and of purpose in nature. The Politics begins with the claim that the city exists by nature and that “man is by nature a political animal.” The Rhetoric (I.11) defines pleasure as a movement by which the soul is restored to its natural state. Readers who want to pursue any of these questions can find the text in the Oxford volumes listed above.

The Most Important Passages for Epicureans

The Canon: How We Know

Knowledge in the strict sense is of what “cannot be other than it is,” and is gained by demonstration: Posterior Analytics I.2.
“Scientific knowledge is not possible through the act of perception”: Posterior Analytics I.31.
From perception to memory, experience and the universal, and the first principles grasped by intuition: Posterior Analytics II.19.
“All men by nature desire to know,” and the ranking of experience, art and wisdom: Metaphysics I.1–2.
The principle of contradiction, “the most certain of all”: Metaphysics IV.3–4.
Against Protagoras and Democritus on appearances, and “Democritus … says that either there is no truth or to us at least it is not evident”: Metaphysics IV.5–6.
Sensation of the special objects is true; imagination is mostly false: On the Soul III.3.
The separable, immortal intellect: On the Soul III.4–5.

Nature, Gods and the Soul

Aristotle’s history of the earlier philosophers, including Anaxagoras’s “mind” and the atomists’ “full and empty”: Metaphysics I.3–4.
Chance, spontaneity and the atomists’ “worlds”: Physics II.4–6.
Purpose in nature, the rain argument and the “man-faced ox-progeny”: Physics II.8.
Against the void, and the equal speeds of bodies in a void: Physics IV.6–9.
Against indivisible magnitudes and motions: Physics VI.1–2 and VI.10.
The eternity of motion and the unmoved first mover: Physics VIII.1, VIII.6 and VIII.10.
The fifth element and the divine heavens: On the Heavens I.2–3.
“God and nature create nothing that has not its use”: On the Heavens I.4.
One world only, and nothing outside it: On the Heavens I.8–9.
The stars as living beings: On the Heavens II.12.
Against the atomists’ motion and their atoms: On the Heavens III.2 and III.4.
Democritus’s method praised, and atomism attacked: On Generation and Corruption I.2 and I.8–9.
The atomic soul of Democritus rejected: On the Soul I.2–3.
The soul as “the first actuality of a natural body”: On the Soul II.1–2.
Perception as receiving “forms apart from their matter”: On the Soul II.12.
Against emanations and “mirroring”: On Sense and the Sensible 2–3.
Dreams are not sent by God: On Prophesying by Dreams 1–2.
God as thought thinking itself, whose “actuality is also pleasure”: Metaphysics XII.6–7.
Myths added “with a view to the persuasion of the multitude”: Metaphysics XII.8.
The universe ordered like an army, and “one ruler let there be”: Metaphysics XII.10.

Ethics

Happiness as the highest good, and the dismissal of the life of pleasure as “slavish”: Nicomachean Ethics I.4–5.
The function argument: happiness is “activity of soul in accordance with virtue”: I.7.
The virtuous life “has its pleasure in itself,” but needs external goods: I.8.
Can the dead be harmed? I.10–11.
Eudoxus “right in his method”: I.12.
Virtue concerned with pleasures and pains, and pleasure “most to be guarded against”: II.3 and II.9.
Voluntary action and responsibility: III.1–5.
Death, “the most terrible of all things,” and the brave man: III.6–9.
The great-souled man and honour: IV.3.
Natural and legal justice: V.7.
The first discussion of pleasure, and the man on the rack: VII.11–14.
Friendship and its three kinds: VIII.1–3.
The second discussion of pleasure: Eudoxus, pleasures higher and lower, and the good man as measure: X.1–5.
Contemplation and “make ourselves immortal”: X.6–8.
Law and compulsion: X.9.

About These Translations

The translations of seven of the works on this site are from The Works of Aristotle Translated into English, the Oxford translation edited by J. A. Smith and W. D. Ross and published by the Clarendon Press between 1908 and 1931:

Posterior Analytics, translated by G. R. G. Mure (Volume I, 1928).
Physics, translated by R. P. Hardie and R. K. Gaye; On the Heavens, translated by J. L. Stocks; and On Generation and Corruption, translated by H. H. Joachim (Volume II, 1930).
On Sense and the Sensible, On Memory and Reminiscence, On Sleep and Sleeplessness, On Dreams and On Prophesying by Dreams, translated by J. I. Beare (first published in 1908, reprinted in Volume III, 1931).
Metaphysics, translated by W. D. Ross (Volume VIII, second edition, 1928).
Nicomachean Ethics, translated by W. D. Ross (Volume IX, 1925).

On the Soul is given in the translation of R. D. Hicks, Aristotle: De Anima, with translation, introduction and notes (Cambridge University Press, 1907). Hicks also translated the Loeb edition of Diogenes Laertius, whose tenth book preserves the letters of Epicurus.

Some points to keep in mind:

The references are Bekker’s. Each page carries Bekker’s page, column and line numbers, as printed in the margins of the Oxford translation. The bold references at the start of each Bekker column link to the page of the scanned Oxford volume at the Internet Archive, so any passage can be checked against the printed book. Every reference is a link target: .../102-aristotle-physics/#198b15 goes to Physics 198b15. For On the Soul, Hicks’s English pages give only the Bekker range of each page, so the references within each page are estimated.
Chapters are the traditional ones, and each has its own link target, such as #ch-2-8 for Book II, Chapter 8.
The translators’ notes are omitted. So are Hicks’s Greek text, his marginal summaries and his commentary.
How the text was prepared. The Oxford texts were prepared from the transcription made for the University of Adelaide’s eBooks@Adelaide, checked word by word against the scanned Oxford volumes. Where the two disagreed, the printed page was followed. This corrected several hundred places where the transcription had dropped or changed words. The Hicks text was prepared by machine reading of the scanned pages and corrected by hand against the page images. Scattered errors may remain in all of these texts, and readers who need certainty about a passage should consult the scan.

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