Part of the Other Perspectives section of the outline of Epicurean philosophy. Updated October 24, 2026.
1. The Demiurge vs. Self-Moving, Eternal Atoms
Plato's cosmos requires a mind to set it in motion: a benevolent craftsman-god who imposes order on inert, pre-existing material. Epicurus's Elementary Principles leave no room for any such incorporeal orderer. Matter is not inert; motion is inherent in the atoms themselves, by virtue of weight, so no external mover -- divine or otherwise -- is needed to explain why the universe moves at all. See the companion article Epicurus and the Pleasure of Rebelling Against Plato, Physics section.
He was good, and one who is good can never have any grudge against anything. And being free from jealousy, he desired that all things should come as near as possible to being like himself.
- Page scan: Plato, Timaeus 29e (tr. Jowett)
- Online text: Plato, Timaeus 29e (tr. Lamb, Loeb) -- Perseus Digital Library
His argument, however, was no worse than that of Aristotle... So with volition, and apart from it the sole causes in the universe were the blind motions of the atoms... Thus to him motion was inherent in matter and no external cause of motion existed, while to Plato matter was inert and the cause of motion was external to it.
[Noting a further point of objection, beyond the parallels catalogued by Munro:] The emphasis laid upon the idea of cause at the outset[,] though for opposite ends. [Both systems open by fixing the idea of cause, Plato to install a designing mind behind the cosmos, Lucretius to deny that any such mind is needed.] ... The common background of chaos derived from Hesiod and the Pre-Socratics[, from which Plato's demiurge imposes order by design, while Lucretius's atoms fall into their combinations by chance collision alone].
2. Being vs. Becoming: An Eternal Realm of "Being" vs. One Continuum of Nature
Before he can describe how the cosmos was built, Plato sorts everything that exists into two kinds: what always is and never becomes, and what is always becoming and never really is. Only what reason grasps -- the Forms -- qualifies as fully real; everything the senses touch is demoted to a lesser, "becoming" status. Epicurus does not simply delete Plato's "Being" -- he relocates permanence into the physical world itself. Compounds arise and perish ("becoming"), but the atoms that compose them do not change at all. Nature runs, without a break, from imperishable atom to perishable compound, and the senses can reach every part of it -- there is no separate, higher order of Being that only reason can enter. See the companion article Epicurus and the Pleasure of Rebelling Against Plato, Physics section.
First then, in my judgment, we must make a distinction and ask, What is that which always is and has no becoming; and what is that which is always becoming and never is? That which is apprehended by intelligence and reason is always in the same state; but that which is conceived by opinion with the help of sensation and without reason, is always in a process of becoming and perishing and never really is.
Moreover, we must suppose that the atoms do not possess any of the qualities belonging to perceptible things, except shape, weight, and size, and all that necessarily goes with shape. For every quality changes; but the atoms do not change at all, since there must needs be something which remains solid and indissoluble at the dissolution of compounds, which can cause changes... For this reason it is essential that the bodies which shift their position should be imperishable and should not possess the nature of what changes, but parts and configuration of their own.
The distinction between permanent and transitory being and the protest, though with different application, against confounding the two by the double meaning of the verb "to be." [Shorey independently names this same issue -- Plato's and Lucretius's shared vocabulary for "being" masking a live disagreement over what, if anything, is permanent -- as one of the clearest points of contact, and of friction, between the two systems.]
Plutarch presents the Platonist view that there are two kinds of ways of being, one of things which properly are (i.e. of the Ideas) and the other, of things which are forever becoming (τὰ γιγνόμενα) [citing Plato, Timaeus 27d5-7 -- the same passage quoted above]. Colotes, a student of Epicurus and nominal target of the work, and the Epicureans in general, are accused of saying that all that, according to them, is part of reality (body and void) exists in the same way [i.e. rejecting Plato's two-tier distinction between real Being and mere Becoming outright, on the authority of Epicurus's own pupil Colotes, in a work titled On the Impossibility of Living According to the Doctrines of the Other Philosophers, aimed squarely at Plato].
3. A Finite, Spherical Cosmos vs. An Infinite Universe
Plato's Timaeus describes a single, finite, deliberately-shaped sphere with no "outside," and therefore no meaningful up or down. Epicurus's universe is infinite in every direction, stocked with an infinite supply of atoms in infinite void. DeWitt notes that Epicurus took direct aim at Plato's finitism by name, refusing even to grant the terms of the argument. See the companion article Epicurus and the Pleasure of Rebelling Against Plato, Physics section.
Plato flouted this theory on the ground that the universe was spherical, which implied that it was finite... Epicurus in a single paragraph essays to immunize the minds of his disciples against certain views propounded by Plato and by Aristotle.
There are infinite worlds both like and unlike this world of ours.
4. Worn, Divisible Geometric Atoms vs. Truly Uncuttable Atoms
Plato, in the Timaeus, imagined the smallest particles of the elements as geometric solids with edges that could wear down over time -- his mechanism for explaining the decay of old age. Epicurus's atoms are by definition "uncuttable," and he devoted a whole treatise, /The Corner in the Atom/, to attacking Plato's geometric-solid theory directly. DeWitt traces the same geometric-atomism to the root of the theory of Forms itself: deny that atoms are perfect, unchanging geometric solids, and the analogy Plato uses to argue from geometry to an eternal Form of Justice collapses with it. See the companion article Epicurus and the Pleasure of Rebelling Against Plato, Physics section.
[DeWitt infers the point of Epicurus's lost treatise /The Corner in the Atom/ from the fact] that Plato had accounted for the phenomena of old age by postulating the detrition of the sharp edges of his angular atoms.
[Epicurus's principles state that] the universe consists of nothing but atoms and void, and that the atoms -- "uncuttable" by definition -- can neither be created nor destroyed.
5. Geometry and Dialectic as the Path to Truth vs. Irrelevant to the Happy Life
Plato's curriculum in the Academy ran through geometry and astronomy as the disciplines that trained the mind to grasp eternal, unchanging truth -- the same faculties that let the philosopher glimpse the Forms. Epicurus threw the whole apparatus out of his own curriculum, rejecting geometry as having no bearing on the happy life. See the companion articles Epicurus and the Pleasure of Rebelling Against Plato, Physics section, and Let All Who Would Free Themselves From the False Claims Of The Geometers Enter Here.
[Plato's Academy curriculum ran through geometry and astronomy as disciplines that trained the mind to grasp eternal, unchanging truth, and thereby to glimpse the Forms themselves.]
In his rejection of dialectic and mathematics Epicurus was motivated partly by his animosity toward Platonism... Geometry was repudiated as having no bearing upon the happy life.
6. God as World-Governor vs. God as Object of Emulation Only
Plato assigned god two distinct jobs: world-governor and object of human emulation. Epicurus, as David Sedley observes, accepted only the second. His gods are worth contemplating and emulating precisely because they are blessed and untroubled -- models of the pleasant life at its most complete -- but they never govern anything. See the companion article Epicurus and the Pleasure of Rebelling Against Plato, Physics section.
Plato had assigned god a double role: world governor and object of human emulation. Epicurus argued vehemently against the first role, but endorsed the second.
Are we born already possessing some kind of awareness of the gods, albeit in a suppressed form, in the way that Platonists believe us to be born with latent knowledge of the Forms? That idea can be quickly eliminated as unacceptable to Epicureans: notoriously, the Platonist version of innatism relies on the hypothesis that the soul pre-existed its present incarnation ... a doctrine which cannot fail to be anathema to any Epicurean.
7. Reason (the Divided Line) vs. Sensation as the Test of Truth
Plato's Divided Line and Allegory of the Cave rank sense-perception at the bottom of a hierarchy topped by reason contemplating the Forms -- the senses show only shadows, and only the trained philosopher who turns from them ever sees the truth. Epicurus's Canon rejects this wholesale and turns it on its head: sensations, anticipations, and feelings -- not reason -- are the tests of truth. See the companion article Epicurus and the Pleasure of Rebelling Against Plato, Canonics section.
In the judgment of Epicurus Plato also ranked as a skeptic, because he belittled the sensations as undependable and phenomena as deceptive, the only real and eternal existences being the ideas.
Not even reason can refute the sensations, for reason depends wholly upon them.
8. Dialectic (Definition by Division) vs. Names As People Find Them
Plato practices /diaeresis/ -- definition by division -- at length in dialogues like the Sophist and the Statesman, elevating categories like "Same," "Other," and "Essence" to the status of fundamental realities. Epicurus considered this "sound without sense" once the Ideas behind such categories were denied, and rejected dialectic as a method through which one could wander for a lifetime without ever touching the question that actually matters: does this get me closer to living well? See the companion article Epicurus and the Pleasure of Rebelling Against Plato, Canonics section.
[DeWitt points to Plato's Timaeus, where categories like "Same," "Other," and "Essence" are elevated to the status of fundamental realities, as exactly the kind of abstraction Epicurus considered "sound without sense" once the Ideas behind them were denied.]
- Page scan: DeWitt, Epicurus and His Philosophy, Ch. VII
Dialectic they reject as superfluous, for it should suffice physicists to get along with the names of things as they find them.
9. The Political, Tripartite Soul vs. Pleasure As Every Creature's Own Guide
Plato's Republic builds its account of the virtuous soul directly out of the structure of the ideal city -- reason, spirit, and appetite in the soul, mirrored by guardians, auxiliaries, and producers in the state -- so that access to the good depends on training and station most people never receive. Epicurus starts from the opposite premise: the good life is something nature communicates directly to every living creature at birth, before it has acquired any opinions at all, and requires no philosopher-king to certify it. See the companion article Epicurus and the Pleasure of Rebelling Against Plato, Ethics section.
Model in words a kind of multifarious and many-headed beast that has, in a circle, all sorts of heads of tame and wild beasts and is able to change and produce out of itself all such growths.
Every living creature, the moment it is born, reaches out for pleasure and rejoices in it as the highest good, shrinks from pain as the greatest evil.
10. Unlimited Desire (the Many-Headed Beast) vs. Pleasure's Natural Ceiling
Plato's many-headed appetitive beast craves more and more without limit -- one reason he denies pleasure can be any kind of stable, self-limiting good. Epicurus insists pleasure has a natural ceiling, fixed by Nature and reachable by anyone regardless of wealth or station: the removal of all pain. DeWitt is explicit that Epicurus established this ceiling directly against Plato. See the companion article Epicurus and the Pleasure of Rebelling Against Plato, Ethics section.
This was the fixed ceiling for pleasure, which he endeavors to establish in opposition to Plato, who compared the appetitive part of the soul to "a many-headed beast" and held to the opinion that desires increase endlessly and that pleasure defied the fixing of a limit.
The removal of all pain is the limit of the magnitude of pleasures, and wherever a pleasant feeling is present, for as long as it is present, there is no feeling of pain.
11. Pleasure As Mere "Becoming" vs. Pleasure As Complete "Being"
Plato argues in the Philebus that pleasure is a /genesis/ -- a "generation," a process aimed at something beyond itself -- and for that reason cannot be /ousia/, real "being." This is the being/becoming distinction from Plato's physics, redeployed against ethics: whatever is merely "becoming" cannot be the good. Epicurus holds that a pleasure is a motion when looked at as it unfolds and a complete state when the whole of a life is in view, with PD3 fixing the exact point of completeness. The Epicureans' own image for that completeness was a /filled/ vessel, not Plato's static "being." See the companion articles Epicurus and the Pleasure of Rebelling Against Plato, Ethics section, and The Completeness Argument, Cicero's Knowledge Of It, And The Epicurean Response.
Then, as I said at first, we ought to be very grateful to him who first pointed out that pleasure was a generation only, and had no true being at all; for he is clearly one who laughs at the notion of pleasure being a good.
...he then perceived that the vessel itself did cause the corruption and that by its corruption all the things that came into it and were gathered from abroad, however salutary were spoilt within it; partly because he saw it to be leaky and full of holes so that it could never by any means be filled full...
12. Mixed Pleasure and Pain vs. Pleasure's Presence Excluding Pain by Definition
Plato's Philebus builds an entire class of "mixed" pleasures -- the itch that is pleasant because it is also painful to scratch, grief mixed with the pleasure of a sad story -- because on his view pleasure and pain can genuinely coincide. Epicurus's PD3 leaves no logical room for that coincidence: wherever pleasure is present in full, pain is simply not there to be mixed in. The ancient commentator Damascius recognized PD3 as a direct rejoinder to Plato on exactly this point. See the companion article Epicurus and the Pleasure of Rebelling Against Plato, Ethics section.
Epicurus thinks that pain cannot [simultaneously] mix with pleasure ... Plato, on the contrary, holds that this does occur, both in the soul and in the body and in combination.
The removal of all pain is the limit of the magnitude of pleasures, and wherever a pleasant feeling is present, for as long as it is present, there is no feeling of pain.
13. The Soul's Pre-Existence and Imprisonment in the Body vs. Soul Born and Dying With the Body
For Plato, the soul exists before birth and may be recollecting truths seen in a prior, disembodied state (the doctrine of /anamnesis/ worked out in the Phaedo and the Meno); life in the body is itself a kind of confinement. Epicurus's soul, by contrast, is born and dies with the body -- there is no pre-existence and no afterlife. See the companion article Epicurus and the Pleasure of Rebelling Against Plato, Ethics section.
[Plato inherited from Pythagoras] the belief that the body was a tomb or prison-house, which blurred the vision of reason and prevented perfection of knowledge.
- Page scan: DeWitt, Epicurus and His Philosophy, Ch. I
There was for Epicureans no pre-existence, as Plato believed, and no afterlife, as the majority of mankind believed.
- Page scan: DeWitt, Epicurus and His Philosophy, Ch. XII
14. The Lover's Flattering Nicknames: A Model of Philosophic Love vs. A Diagnosis of Self-Deception
Paul Shorey notes that H. A. J. Munro, in his edition of Lucretius, had already catalogued a set of close verbal parallels between Lucretius and Plato that most likely reached Lucretius by way of Epicurus. This is not a case of agreement: Plato and Lucretius describe the identical human habit -- lovers coining flattering pet names for a beloved's physical defects -- and draw opposite morals from it. Socrates uses the catalogue approvingly, as a charming illustration of how the true philosopher, like an indiscriminate lover, finds something to love in every kind of knowledge. Lucretius uses the identical catalogue as a clinical diagnosis of the self-deception bred by uncontrolled passion, immediately before warning that this same blindness is what traps a man in the "strong bonds of Venus." Same observation of human psychology; opposite verdicts on whether it is admirable or a warning sign to be guarded against.
Source of this observation: Paul Shorey, "Plato, Lucretius, and Epicurus," /Harvard Studies in Classical Philology/, Vol. 12, Goodwin Volume (1901), pp. 201-210, footnote 1 on p. 204-205, where Shorey lists "the hypocoristic lover 4, 1160 with Republic 474 D" among the parallels he says are "cited by Munro."
Is not this a way you have with the fair: one has a snub nose, and you praise his charming face; the hook-nose of another has, you say, a royal look; while he who is neither snub nor hooked has the grace of regularity; the dark visage is manly, the fair are children of the gods; and as to the sweet "honey pale," as they are called, what is the very name but the invention of a lover who talks in diminutives, and is not averse to paleness if appearing on the cheek of youth? In a word, there is no excuse which you will not make, and nothing which you will not say, in order not to lose a single flower that blooms in the spring-time of youth.
For this men usually do, blinded by passion, and attribute to the beloved those advantages which are not really theirs. We therefore see women in ways manifold deformed and ugly to be objects of endearment and held in the highest admiration... The black is a brune, the filthy and rank has not the love of order; the cat-eyed is a miniature Pallas, the stringy and wizened a gazelle; the dumpy and dwarfish is one of the graces, from top to toe all grace; the big and overgrown is awe-inspiring and full of dignity.
15. The Soul Feared to Disperse Like Smoke vs. The Soul That Actually Does
In the Phaedo, Cebes voices the ordinary person's fear about death: that the soul, on leaving the body, might simply disperse like smoke or breath and vanish into nothing. Socrates treats this as a fear to be argued away, and spends the rest of the dialogue building proofs that the soul is imperishable. Lucretius takes the identical image -- the soul dissolving like smoke -- and affirms it as the literal, physical truth, then draws the opposite conclusion from Socrates: since the soul cannot survive the body's dissolution, there is no posthumous subject left to suffer, and death is nothing to fear. Both philosophers start from the same picture of what death might mean for the soul; one treats it as the nightmare to be disproven, the other as the sober fact that removes the nightmare.
Source of this observation: Paul Shorey, "Plato, Lucretius, and Epicurus," /Harvard Studies in Classical Philology/, Vol. 12, Goodwin Volume (1901), pp. 201-210, footnote 1 on p. 204-205, where Shorey lists "the dissipation of the soul like smoke or vapor, 3, 456 with Phaedo 70" among the parallels he says are "cited by Munro."
[Men fear] that when [the soul] has left the body her place may be nowhere, and that on the very day of death she may perish and come to an end -- immediately on her release from the body, issuing forth dispersed like smoke or air, and in her flight vanishing away into nothingness.
It naturally follows then that the whole nature of the soul is dissolved, like smoke, into the high air; since we see it is begotten along with the body and grows up along with it and, as I have shown, breaks down at the same time worn out with age.
16. The Child's Fear of the Dark: Cured By Proof of Immortality vs. Cured By Nature
Both philosophers reach for the identical image of a child terrified of imaginary hobgoblins in the dark as their picture of the irrational fear of death -- and both propose an antidote administered like a "charm," repeated until the fear is gone. There the agreement ends. Socrates's charm is philosophical argument for the soul's immortality: face the fear down by proving there is no ultimate loss to fear. Lucretius's charm is the opposite doctrine applied to the same fear: not the light of the sun, but the study of nature, showing that the soul does not survive to suffer anything after death at all. The two men agree, almost word for word, on the diagnosis and on the method of cure (a repeated argument, not brute reassurance) -- and flatly disagree on which argument does the curing.
Source of this observation: Paul Shorey, "Plato, Lucretius, and Epicurus," /Harvard Studies in Classical Philology/, Vol. 12, Goodwin Volume (1901), pp. 201-210, footnote 1 on p. 204-205, where Shorey lists "the comparison of our fear of death to the terrors of children in the dark, 2, 55, Phaedo 77 E" among the parallels he says are "cited by Munro."
There is a child within us to whom death is a sort of hobgoblin; him too we must persuade not to be afraid when he is alone in the dark. ... Let then the voice of the charmer be applied daily until you have charmed away the fear.
- Page scan: Plato, Phaedo 77d-e (tr. Jowett)
- Online text: Plato, Phaedo 77d (tr. Fowler, Loeb) -- Perseus Digital Library
For even as children are flurried and dread all things in the thick darkness, thus we in the daylight fear at times things not a whit more to be dreaded than what children shudder at in the dark and fancy sure to be. This terror therefore and darkness of mind must be dispelled, not by the rays of the sun and glittering shafts of day, but by the aspect and law of nature.
17. Articulate Speech As A Divine Gift vs. Articulate Speech As Mere Anatomy
In Protagoras's myth, man invents "articulate speech and names" only once he already possesses the divine-derived skill stolen from the gods by Prometheus -- language belongs to a story of theft from, and kinship with, the gods. Lucretius locates the same capacity for articulate speech in nothing more exalted than the tongue and lips mechanically shaping breath forced up from the chest -- an entirely natural, anatomical account with no myth and no debt to any god, consistent with his fuller argument elsewhere (Book V) that language grew up by natural utility, not divine bestowal.
Source of this observation: Paul Shorey, "Plato, Lucretius, and Epicurus," /Harvard Studies in Classical Philology/, Vol. 12, Goodwin Volume (1901), pp. 201-210, footnote 1 on p. 204-205, where Shorey lists "the use of articulat[e] 4, 551 with that of διηρθρώσατο Protag. 322 A" among the parallels he says are "cited by Munro."
Now man, having a share of the divine attributes, was at first the only one of the animals who had any gods, because he alone was of their kindred; and he would raise altars and images of them. He was not long in inventing articulate speech and names.
When therefore we force these voices forth from the depths of our body and discharge them straight out at the mouth, the pliant tongue, deft fashioner of words, gives them articulate utterance and the structure of the lips does its part in shaping them.
18. Justice As A Strawman To Be Refuted vs. Justice As The Correct Account
Glaucon, at the opening of Republic II, states the conventionalist theory of justice -- that it is merely a compact among the weak, neither to do nor suffer wrong, adopted only because no one is strong enough to always get away with injustice -- precisely so that Socrates can spend the rest of the dialogue refuting it in favor of justice as an intrinsic good, part of the soul's own health, worth choosing even for a man wearing the ring of Gyges. Epicurus does not answer this challenge on Plato's terms. He embraces, as the correct and sufficient account of justice, exactly the compact-among-the-weak theory Glaucon offers as a foil to be defeated. There is no deeper metaphysical fact -- no Form of Justice, no intrinsic virtue of the soul -- for Epicurean justice to answer to.
Source of this observation: Paul Shorey, "Plato, Lucretius, and Epicurus," /Harvard Studies in Classical Philology/, Vol. 12, Goodwin Volume (1901), pp. 201-210, footnote 1 on p. 204-205, where Shorey lists "the social compact 5, 1020 with Republic 358-359" among the parallels he says are "cited by Munro."
They say that to do injustice is, by nature, good; to suffer injustice, evil... when men... have had experience of both, [and being] not able to avoid the one and obtain the other, they think it expedient to make a compact with one another to have neither... this they affirm to be the origin and nature of justice; it is a mean or compromise between the best of all, which is to do injustice and not be punished, and the worst of all, which is to suffer injustice without the power of retaliation.
Then too neighbors began to join in a league of friendship mutually desiring neither to do nor suffer harm; and asked for indulgence to children and womankind... And though harmony could not be established without exception, yet a very large portion observed their agreements with good faith, or else the race of man would then have been wholly cut off, nor could breeding have continued their generations to this day.
19. The Soul As "Attunement": Refuted By An Argument From Degree, Then Mocked By The Same Argument Turned On Itself
In the Phaedo, Simmias proposes that the soul is merely an "attunement" (harmonia) of the body, the way a lyre's tuning is a property of its strings. Socrates refutes this with an argument from degree: no soul is more fully a soul than another, but attunement plainly does come in degrees (an instrument can be more or less in tune), so soul and attunement cannot be the same thing. David Sedley reports that Epicurus, whose own opposition to Plato's dialectic was total, did not answer this with a rival theory of the soul but with a parody exposing the argument-form itself as worthless: sweetness comes in degrees, Epicurus pointed out, yet no one concludes that honey itself is therefore "not really honey." If Socrates's inference were valid, it would dissolve identities everywhere, not just refute the harmony theory -- proof, for Epicurus, that this kind of argument by degree is a trick of dialectic rather than a genuine path to truth, exactly the complaint pressed at length in the Canonics section of the companion article Epicurus and the Pleasure of Rebelling Against Plato.
We have already admitted that no soul is more a soul than another; which is equivalent to admitting that harmony is not more or less harmony, or more or less completely a harmony... And that which is not more or less harmonized cannot have more or less of harmony, but only an equal harmony... And having neither more nor less of harmony or of discord, one soul has no more vice or virtue than another, if vice be discord and virtue harmony.
[Sedley's summary of the testimony:] Epicurus' parodic equivalent [to Socrates's argument in the Phaedo] was to argue that in that case honey is not (or not essentially?) sweet, on the grounds that there are degrees of sweetness but not of honey.
- Page scan: David Sedley, "Epicurus on Dialectic," p. 88, citing Philoponus, In Aristotelis De Anima 143.3-6
- Online text: Epicurus, testimony preserved in Philoponus, In Aristotelis De Anima, reported in David Sedley, "Epicurus on Dialectic," in Epicurus and Philosophical Debates in the Hellenistic and Roman World (2024) -- Perseus Digital Library (Diogenes Laertius X, tr. Hicks, Loeb)