Leucippus and Atomism

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Leucippus and Atomism



Man of Mystery . Certainly the most original fifth-century contribution to the debate on the nature of change was that of Leucippus (Leukippos) of Miletus. Little is known about his life, except that he lived around 430 b.c.e., wrote two books (On Mind and The Great World System), and was the teacher of the famous Democritus of Abdera. It is through his pupil that Leucippus’s revolutionary insights into the world of nature have mainly been preserved. In turn, the list of works attributed to Democritus runs to more than seventy titles, and includes studies on such diverse subjects as mathematics, farming, medicine, grammar, ethics, and literature. In what remains of his writings on physics or natural science, the atomic theory that Leucippus proposed and Democritus further developed marks a highpoint in ancient speculation.

The Atom . The main features of this theory are direct responses to the demand for an eternally changeless reality offered by Parmenides; and like the answer of the Pluralists, the Atomists too adopted an Eleatic description of their fundamental substance. This material was the atom—from the Greek word atomon, meaning “indivisible.” Each atom is ungenerated, uniform, unalterable, and incapable of any further division. (Note that this last characteristic distinguishes ancient Greek atoms from the splittable ones of modern physics.)

Three Differences . Infinite in number, the atoms of Democritus differ from each other in three respects only: shape (as the letter ‘A’ differs from ‘N’), arrangement (as ‘AN’ differs from ‘NA’, and relative position (as ‘N’ is ‘Z’ turned on its side). Their different shapes are countless, ranging from the smooth, rounded atoms that compose water to the rough, jagged, and uneven ones out of which iron is made. The only other natural reality allowed by Leucippus and Democritus is an infinite void that separates each atom from the others and provides the empty space in which they all continuously move in all directions, often with a whirling motion, and bump into each other. Chance collisions among atoms account for the world of sense experience, since the couplings of hooked atoms or atoms whose shape in some way fit that of others give rise to compound objects. In a fragment from his lost work on Democritus, Aristotle explains the theory as follows:

The atoms are carried about in the void . . . and as they are carried about, they collide and are bound together in a binding that makes them touch and get close to each other, but which does not actually produce any other single thing. . . . He explains how these entities remain together by reference to how the atoms get entangled with and stuck to each other. For some of them are rough, some hooked, some concave, some convex, and others have countless other different aspects. He thinks they keep hold of one another and stay together until such time as a stronger force from outside touches them, shakes them, and scatters them apart.

Infinity . The apparent coming-to-be and passing-away of things is thus really a rearrangement—joining and separation—of invisible, infinite, and indestructible entities. Moreover, since atoms and void are both infinite, and since motion has always existed, Democritus believed that there must have always been an infinite number of worlds. Each is made of precisely the same unchangeable atoms in different configurations.


Heraieus of Mytilene. He had no hair on his head, but an abundant growth on his chin. He was ashamed because he was laughed at by others. He slept in the Temple. The god, by anointing his head with some drug, made hair grow there.

Arata, a woman of Lacedaemon [in southern Greece], suffering from dropsy. While she remained in Lacedaemon, her mother slept in the Temple and saw a dream. It seemed to her that the god cut off her daughter’s head and hung up her body in such a way that her throat was turned downwards. Out of it came a large quantity of fluid. Then he took down the body and fitted the head back on the neck. After she had seen this dream the mother went back to Lacedaemon, where she found her daughter in good health. She had seen the same dream.

A man with an abscess in his stomach. When asleep in the Temple he saw a dream. It seemed to him that the god ordered the servants who accompanied him to grip him and hold him tightly so that he could cut open his abdomen. The man tried to get away, but they gripped him and bound him to a door knocker. Then Asclepius cut his belly open, removed the abscess and, having stitched him up again, released him from his bonds. Then he walked out sound, but the floor . . . was covered with blood.

Source: Emma Edelstein and Ludwig Edelstein, Asdepim: Collection and Interpretation of the Testimonies (Baltimore & London: Johns Hopkins University Press, 1945).

Senses . Both the breadth of Democritus’s interests and the rational consistency of his atomism are clear from how he applied his theory to explain sense perception, and so also to address the problem of knowledge. First, he believed that our experience of the world is ultimately sensual, the result of physical contact between atoms streaming from objects and entering our organs of perception. Waves of atoms thrown off the surface of a table, for instance, make a kind of impression in the air which then passes as an image into a person’s eyes. Different shapes and arrangements of atoms are directly responsible for the variety of possible sensations. For example, the atoms of honey are generally round and smooth in shape, in contrast to the sharp, thin ones of a pungent substance such as vinegar.

Illusion . The data provided by the five senses concern only the shape and arrangement of atoms, however, not the atoms themselves. Everything perceived by the senses is therefore “secondary” and, in a sense, unreal. The chance combinations of atoms do not “actually produce any other single thing,” but instead only create the illusion of permanent objects. In actual fact, the atomic arrangements responsible for our sensations of sight, sound, taste, touch, and smell are really impermanent and illusory. The only things that truly exist are atoms per se and the void. Since the senses cannot provide direct access to atoms themselves, only to their shapes and configurations, the rational mind alone has claim to knowledge of reality.


David Furley, Two Studies in the Greek Atomists (Princeton: Princeton University Press, 1967).

Samuel Sambursky, The Physical World of the Greeks (New York: Macmillan, 1956).