The Atomism of Democritus

An Introductory Essay by Dr. Jan Garrett

Most Recent Modification October 10, 2003


Democritus of Abdera lived from about 460 to 370 B.C. Along with Leucippus, an older philosopher whose dates are uncertain, he is the founder of the atomic philosophy of nature. Atomism is the most influential of the philosophies of nature to be developed prior to the time of Socrates (d. 399 B.C.). With Socrates the interest of philosophy shifts for awhile away from nature. After Aristotle's death the atomist philosophy is revived, with some modifications, by Epicurus. In the Roman period it was popularized in its Epicurean form in Lucretius' lengthy poem On the Nature of the Universe. In the seventeenth century (i.e., before the development of what can be recognized as modern chemistry), something like ancient atomism was revived in the philosophy of Pierre Gassendi.

Immediately following is your instructor's reconstruction of the Democritean philosophy, based on the surviving fragments of Democritus himself. The "fragments" are citations and paraphrases of Democritus' writings found in various ancient authors. We do not possess any complete text from Democritus. The interested student is invited to look up the extant fragments of Democritus in any collection of the writings of the Pre-socratics. See "For Further Reading" at the end of this essay.

I. Background: Early Natural Philosophy

From the beginning of natural philosophy people have wondered about the ultimate cause or nature of the physical world. Sometimes the inquiry has taken them in the direction of a controlling power, a single divine force or principle which governs the multiplicity and changes which can be observed by the senses.

At other times inquirers have been led to ask about the components or parts of the bodies that seem to make up the physical world. How many of them are there? Can they be classified into kinds on the basis of similarities? How do they interact with one another? How minutely can they be divided? If there is a limit to their divisibility, what are the ultimate bodies like?

Early thinkers about nature were impressed by the apparent pervasiveness of opposites or contraries in nature, for instance, hot and cold, up and down, wet and dry. For any such pair, the first is not the second, and vice-versa. For each member of each pair, it is itself, and is not its opposite.

Yet motion or change seems to be pervasive as well; short things grow tall; wet things become dry; big things shrink to small ones (for example, cut grass left in the sun). For any part or segment of such processes, being is mixed with not-being. For instance, at any interval in a process of growth (becoming large from having been small [not-large], being-larger seems to be mixed with not-being-larger.

Heraclitus (ca. 500 B.C.) is a philosopher who takes such observations to heart; for him, reality is characterized throughout by the unity of opposites. Everything that is, is also its opposite. As he puts it poetically, "the road up and the road down are one and the same."

II. The Absolute Existents: Atoms

Yet the atomists, who prefer a more logical and less poetic way of speaking, do not agree with him. Where existence or reality is concerned, there must be something that fully and unambiguously exists, with no admixture of nonbeing. It is one thing to talk about small things not being large, or wet things not being dry, or Homer (who lived earlier than Hesiod) not being later than Hesiod. Yet when it comes to existence, in the unqualified sense, some things must exist absolutely. Something must be absolutely before we can truly speak of its not being in a qualified sense (for instance, not-hot, not-cold, not older, not-younger).

Atomists hold that the absolute existents are the ultimate parts or components of visible bodies, though these absolute existents can exist separately from these visible bodies. These existents are completely full or solid; they contain no gaps, no holes, no empty places. They cannot be subdivided, cut, cracked, split, or penetrated; for this would imply that nonbeing has gained a foothold in them. These absolute existents are called atoms, from the Greek word atomon, which means "that which cannot be divided."

Atoms do not come into being or pass away; for if they come into being (or pass away), then they would have to partially exist and partially not exist; but partial existence makes no sense for ultimate things.

The "parts" of atoms do not move relative to one another. (Of course, atoms do not have parts if by "parts" we mean components that can be detached from one another, but we can think of atomic "parts" if we can think of the left and right sides of an indissoluble solid.) These "parts" could move relative to one another only if the atoms were not completely solid. However, atoms are completely solid. Thus, atoms are entirely inflexible.


II. The Void

The atomist philosophy would be extremely simple if it could limit itself to saying that ultimately only the atoms exist (with visible bodies gaining their [dependent] existence from the atoms that make them up). Now, what would reality be like if only atoms existed? Reality would be filled up, in every direction, with atoms. At the limit of one atom, there would be another atom; there would, in fact, be no point on any surface of any atom that failed to touch the surface of a neighboring atom. Each atom would be hemmed in on all sides by others. No atom could move relative to other atoms. In fact, no change of any sort would be possible.

If this were so, it might even make sense to say that there is just one atom, infinitely large in all directions, for there would be no gaps between the "parts" of this monstrous solid, and these parts could never come apart. If this were true, philosophy would find itself in the position of Melissus of Samos,[1] according to whom there is just one thing, which is indivisible, while change, motion, and plurality--the existence of more than one thing--are illusions.

However, Democritus' predecessor, the atomist Leucippus, indicated a way out. Atomists can keep the doctrine of the atoms, together with the testimony of the senses regarding the existence of change and plurality, provided that they are willing to admit some role for not-being.

To clarify this point, let it be said that atomists do not wish to admit all sorts of not-being. The only ultimate kind of not-being they admit is the void, that is, empty extension which stretches upwards, downwards, forwards and backwards, to the left and to the right (from whatever position one chooses to measure) infinitely, without end.

Of course, it is not entirely empty, because in it there are the dense, indestructible atoms. Apart from these atoms (and the larger compound bodies of which the atoms are sometimes parts), there is nothing but the infinite void.

Leucippus and Democritus maintain the existence of atoms and the void in part because, thanks to notions of atoms and the void, philosophers are able to explain, or give a rational account (logos) of, the observable world-order (kosmos), of how things come into being and pass away. What ultimately is, atomists say, is the atoms, and the not-being called the void also is. Neither of these come into being or pass away. Since they exist in a basic sense, they cannot cease to be; they are everlasting.

IV. Answers to Objections

These atoms are too small to be visible to the naked eye, but from them composite bodies, aggregates of atoms, "come to be." These composites are frequently large enough to be visible--we ourselves are composites of atoms. Composites "grow" through the addition of atoms to those that provide an initial core; they "pass away" through the separation of atoms from the composite.

You may think it absurd to suppose the existence of entities which even atomists, who proclaim their existence, admit to be so small that they cannot be perceived individually. But when you look out of a sturdy building and see trees swaying, you do not deny the existence of the wind, though you cannot perceive it directly. The reason is that you observe its effects, for example, in the swaying of trees.*(2)

Atoms too are revealed through their effects. You will admit that wet clothes hanging in the sun gradually become dry; imperceptibly, the water leaves them. Atomists say that this occurs because atoms leave the clothes one at a time, and individually they are not visible. (The other alternative would seem to be that the water simply ceases to be--a point which seems absurd; for if water could simply cease to be, why has not the whole world turned to desert by now?)*

Atomism teaches that all visible objects, which are composites or collections of linked atoms, have within them a good amount of void, though some have more than others. Perhaps you find it difficult to accept that hard objects are actually partially composed of void. But you will admit that sounds travel through walls that look solid; heat will travel through metals; light will travel through glass. This would not be possible, atomists maintain, unless these were full of "pores," that is, small quantities of void between the atoms of the composites. Atoms that cause our sensation of heat are able to get through metals, atoms that cause our sensation of color are able to pass through glass, and so forth.*

And how do you explain why a block of wood and an equally large hunk of lead have different weights? The answer, according to the atomists, must be that these objects have different quantities of void within them.*

V. Atomic Diversity

How many kinds of atoms are there? If atoms were of just one kind, that is, if they all had the same shape and size, then we would not experience the variety of nature which we actually do experience. Different effects require different causes. Our experiences are the effects of which the atoms--their shapes, sizes, arrangements and movements--are the causes.

Some interesting differences in experience are the direct result of differences in kind of atoms--in their size and/or shape. For example, sweet tastes are caused by round atoms, of a good size. Sour tastes are caused by atoms that are bulky, jagged, and many-angled, without curves. Pungent tastes are caused by atoms that are round, fine, angular and crooked. Salty tastes are caused by angular atoms which are of a good size, twisted, with two sides equal. Bitter tastes arise from atoms that are curved and smooth but very crooked and small in size. Oily tasting things consist of atoms that are fine, round and small. [Source: Robinson, An Introduction to Early Greek Philosophy (1968), p. 200]

Each kind of atoms--by "kind of atoms" is meant a group of atoms alike in shape and size--must include a very large number of atoms. For example, if there were not a virtually endless supply of the atoms which cause us to see surfaces as green in color or to taste foods as sweet, our visions of green things and tastes of sweet things would be far more limited than they actually are.*

Besides differing in kind, atoms also differ in how they are ordered and "turned" relative to one another. One can illustrate the point using as examples letters of the alphabet. A large A and a smaller A differ in size. A and H differ in shape. AN and NA differ in ordering. Z and N differ in turning. Some of the differences we experience arise not from differences in the shapes or sizes of the atoms encountered, but in how they are combined (in what order) or in how they are turned. [Source: Aristotle, Metaphysics 985b4-b18]

VI. Atomism and the Soul

Some people believe that living beings, or animals, or perhaps just human beings, are distinct from other composite bodies -- they claim that besides the minute bodies that make up any visible body, these beings, or some of them, possess something that survives death. The atomist view is that this is unlikely. Animals, of course, do possess something which rocks lack--they possess life and breath; but in the atomist view this "soul" is nothing more than a special very small, fast-moving group of atoms that operate within the living being and help it sense and act upon its environment. Human beings, of course, have the power of thought, but in the atomist view thought is nothing but a special way of being alive and an animal.

Every animal contains a complex system of tiny tubes. These extend between the sense organs, on or near the exterior of the body, and the mind, or center of consciousness, probably in the chest area. How sensation occurs can be explained as follows: Atoms from external objects strike the sense organ and push into movement small soul atoms in tubes near the organs; these small atoms jog their further neighbors into movement, and these in turn jog their neighbors; the motions travel very quickly through the tiny tubes, eventually arriving at the mind, or center of consciousness.*

How mental decisions cause physical motions can be explained as follows: The decisions of the mind, by which our ideas of what we wish to do cause our limbs to move or our lips to speak, are in themselves nothing but special movements of atoms in the center of consciousness. Motion from these atoms is communicated to the muscles in the body's remote members through tubes similar to, or the very same as, those involved in perception, only in the reverse direction.*

Because, for atomism, the soul or "life" of an animal is nothing but a collection of atoms that exist and operate together only if they are encased in a body, the soul cannot survive the destruction of the body. When the soul is destroyed, it is broken up, and as that happens, the atoms that once made up the soul scatter just as water in a jar will scatter when the jar is broken. Because the body passes away, the soul does also. Of course, the atoms of which the soul and body are composed do not cease to be--no atom comes into being or passes away--but atoms individually are not alive (how could anything totally inert be alive?), so there is no place for immortality in the philosophy of atomism.

VII. Two Kinds of Knowledge

Atomists teach that there are two kinds of knowledge, genuine and illegitimate. Genuine knowledge tells us about the atomic structure of things, and concerns the size, shape, arrangement and turning of the atoms. Yet what most mortals take to be knowledge is nothing of the sort; they speak of colors, smells, tastes, and so on--the experiences which are revealed to our senses. But our senses by themselves reveal nothing of the true reality which underlie them.

According to atomists, among the atoms and the void, there are no colors, smells, sounds, tastes: these are experiences born of the impact of atoms upon our senses (themselves aggregates of atoms). We all know that if our senses are altered, as occurs when a sick person becomes healthy, the same external stimulus produces a different experience. Therefore, the senses, without the true interpretation provided by the atomist philosophy, tell us nothing about reality. They give us only an illegitimate knowledge.

Democritus would not deny that it is of some use for mortals to have "illegitimate knowledge," to think, for example, that something is hot even though they may have no idea about the nature of the atoms that cause this sensation. Yet philosophers like him do not seek knowledge for the sake of utility; they seek to know for the pure joy of understanding.


1. The philosophy of Melissus of Samos is a variation of the Eleatic philosophy whose original source is Parmenides (b. ca. 515, d. after 450 B.C.), a much more profound (and difficult) thinker.

2. Arguments in the asterisked paragraphs have as their textual basis Lucretius' lengthy work in the atomist tradition deriving from Epicurus. I have felt justified in attributing them to the philosophy of Democritus because they seem to pertain to the parts of the theory shared by Democritus and the Epicureans. In my view, Democritus might have made these arguments, but I cannot claim as a matter of historical knowledge that he did.

For Further Reading

Allen, R. E., ed. Greek Philosophy: Thales to Aristotle. New York: The Free Press, 1991. Contains many of the surviving original fragments of the Presocratics, including Democritus.

Brumbaugh, R. S. The Philosophers of Greece. Albany: State University of New York Press, 1981. Chapter 9.

Guthrie, W.K.C. The Greek Philosophers: From Thales to Aristotle. New York: Harper and Row, 1960. Chapter 3.

Hussey, Edward. The Presocratics. New York: Charles Scribner's Sons, 1972. Chapter 7.

Lloyd, G. E. R. "Leucippus and Democritus." Encyclopedia of Philosophy, vol. 4, pp. 446-451. (Available in Reference Room, at WKU Library.)

McKirahan, Richard D. Philosophy Before Socrates. Indianapolis: Hackett, 1994. Chapter 16.

Ring, Merrill. Beginning with the Presocratics. Palo Alto, CA: Mayfield Publishing Company, 1987. Chapter 10.

This web version of "The Atomism of Democritus" is based on an article designed for use by Introduction to Philosophy students. Its most recent substantial revision was no later than July 1995.