The Atomic Theory

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The Atomic Theory

Escaping the Logic of the Eleatic School.

Both Empedocles and Anaxagoras attempted to evade the ruthless logic of Parmenides and the Eleatic School of philosophers who argued that there are two opposites, "that which exists," which is matter, and "that which does not exist," which obviously does not exist. Since the world is composed of matter which does exist, it fills all the available space. Thus there can be no motion, for motion implies that there is empty space into which an object in motion can move, and there is no empty space. Parmenides' follower, Zeno, proved to his own satisfaction that an arrow in flight only appears to move. In actuality, at any given point in its apparent flight, it is at rest. To escape from this logic, someone had to produce a theory to prove that empty space was not the same thing as the Eleatic's "that which does not exist." The philosopher who provided the necessary leap of imagination to get over this Eleatic idea was Leucippus of Miletus, the same city that fathered Thales, Anaximander, and Anaximenes who had started the long tradition of Greek speculation about the nature of the universe. Unlike his predecessors, he is a shadowy figure, overshadowed by his more famous follower Democritus to such an extent that some Greeks even denied his existence. He was recognized, however, by such philosopher greats as Aristotle, who headed the school known as the Lyceum in Athens of the fourth century b.c.e., and his successor Theophrastus. Both men referred to Leucippus as the author of a work on the atomic theory titled the Great World System, although other philosophers—notably Epicurus (342–271 b.c.e.) and his followers—attributed this theory to Leucippus' pupil, Democritus of Abdera. Although Democritus was a prolific writer, none of his works survive to the present day.

The Atoms of Leucippus and Democritus.

Leucippus and Democritus conceived of particles of matter called "atoms" which moved through space like the flecks of dust that can be seen moving in a sunbeam. Some were large, some small, and some might be smooth and round and others might have an irregular shape. The atoms moved through void. Parmenides had argued that the universe was a plenum filled with matter, and there was nothing else, but Leucippus and Democritus argued that the opposite of a plenum—a vacuum—also existed. Each atom, however, which was so small as to be invisible, was itself a plenum, and could not be split. Atoms were atoma somata (bodies that cannot be divided). The atoms were perpetually spinning, like the "seeds" of Anaxagoras, and as they collided some stuck together while others were forced apart. Small, perfect atoms gravitated towards the outside of the universe and formed the dome of the sky, whereas heavier atoms gravitated towards the center and formed earth. The concept of weight and its opposite, lightness, was something the Greeks did not understand, for the force of gravity had not yet been defined. Leucippus explained that weight resulted from the size of the atoms and their combinations, but neither he nor Democritus seemed to have thought weight very important and they never committed the error that Aristotle made later, of arguing for the existence of absolute weight. Epicurus later assigned different weights to the atoms, and argued that the heavier atoms moved at a different speed than the lighter ones. For Leucippus and Democritus, weight was a relative thing and the atoms moved at random. But they collided, and from their collisions they formed the groups of atoms that make up every object in this world, including human beings. The atomists saw an analogy in the letters of the alphabet. Each letter is a separate symbol with its own form, but when arranged together in various ways they form words. So the various arrangements of the atoms form different objects in the same way as the different arrangements of letters make different words. It was taken for granted that the atoms would always keep moving unless something intervened to make them stop.

The Problem of the Soul.

The atomic theory of Leucippus and Democritus assumed that the soul, too, was made up of atoms and void. Soul atoms were round and very mobile, and the atomists argued that there was also a fiery quality about them. Fire-atoms exist in the universe, but had no influence on how material things move; men breathed them into their bodies, at which point they formed an aggregate of fiery atoms known as the soul, and on death, it dissolved. This theory hearkened back to the old Greek belief that the soul—the psyche—was the breath of life which departed from the body at death. According to the atomic theory, the soul that is composed of atoms leaves the body when the last breath is drawn and returns to mingle with the fire-atoms of the universe. There is no place in this theory for any belief in the immortality of the soul. Yet the soul that is within every living person endows him with his intellect and his senses and even governs the motion of his limbs. The senses allow humans to see, hear, and taste, for objects project images of themselves as emanations, and these are received by the soul. Animals apparently did not have souls of this sort, though they, too, breathed in air and exhaled it, and in fact, the concept of the soul according to the atomic theory seems to involve a good deal of inconsistency.

Democritus the Moralist.

Democritus wrote on a remarkable number of subjects, including mathematics, and among them was a theory of ethics which he fitted to his atomic philosophy. One treatise titled On Cheerfulness began with a warning against restless activity. Freedom from disturbance, he wrote, is what brings about human happiness. Cheerfulness is the ultimate good and it is a state in which the soul lives tranquilly, without being disturbed by any fear or superstition. Here we find a new conception of life for a person, not as a part of a social order such as a city, but rather as an individual. Human happiness was the sum total of all feelings that give pleasure—not just vulgar pleasures, though Democritus did not rule them out, but also pleasures in the beautiful. His thoughts about the gods are difficult to discern; one surviving fragment of his writings refers to them as providers to mankind of all that is good, and another fragment mentions them as images that approach human beings to impart knowledge of the future and of the divine. On morals, he was no relativist. As far as he was concerned, there was one standard of morality for everyone:

The same things are good and true for all mankind, but some men take delight in some things and others in others.


Paul Cartledge, Democritus (London, England: Routledge, 1999).

Marshall Clagett, Greek Science in Antiquity (London, England: Abelard-Schuman, 1957).

Thomas Cole, Democritus and the Sources of Greek Anthropology. American Philological Association Monograph, no. 25 (Cleveland: Press of Case Western Reserve University, 1967).

George N. Vlahakis, "Atomism," in Encyclopedia of Greece and the Hellenic Tradition. Vol. 2. Ed. Graham Speake (London, England: Fitzroy Dearborn, 2000): 201–202.

Gregory Vlastos, "Ethics and Physics in Democritus," in Studies in Greek Philosophy. Ed. Daniel W. Graham (Princeton, N.J.: Princeton University Press, 1996): 328–350.

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The Atomic Theory

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