460 - 370 BC
Democritus was a Greek philosopher and one of the chief exponents of atomism. Democritus' explanation of the universe as made up entirely of minute particles (atoms) moving in empty space (the void) is considered the prototype of materialistic, mechanistic cosmologies.
Democritus was born in Abdera, in Thrace, probably about 460 BC. Although this date makes him 10 years younger than Socrates, he is rightfully considered the last of the pre-Socratic cosmological speculators. The atomic theory developed by Democritus was originally postulated by his teacher Leucippus. However, it is impossible to determine what each of these philosophers contributed to the theory.
Democritus was a prolific writer, but unfortunately only a meager remnant of his writings has been preserved. The ancient catalogs list over 60 works on a wide variety of topics, including cosmology, epistemology, ethics, astronomy, geography, medicine, mathematics, linguistics, and musical theory. Democritus' reputation for self-sufficiency, serenity, and cheerfulness is confirmed by the extant ethical fragments. Reports that he traveled extensively in pursuit of his investigations are probably exaggerated.
The atomists attempted to reconcile the obvious facts of the sensible world with the arguments of the Eleatics (Parmenides, Zeno, and Melissus), who denied the reality of the physical world and the possibility of change. The Eleatic dictum "Nothing cannot exist" was interpreted by the atomists as a denial of the existence of empty space (the void). The atomists thought that by positing the existence of the void they would be able to escape the paradoxes of the Eleatics and account for change and the physical world.
According to Democritus and Leucippus, the world consists of an infinite number of atoms that move in the void. Atoms are imperceptible, eternal particles, which, as their name implies, cannot be divided. They are said to differ only in shape, arrangement, and position, though they would also seem to differ in such qualities as size and speed. Each sensible object is a conglomeration of atoms: the more stable bodies are composed of atoms that are interlinked; the more fluid substances are made of atoms that do not intertwine. Perceptible change is a result of the movement, collision, and rebounding of atoms.
Sensation and thought are likewise explained by Democritus as effects of atoms in motion. Sensation arises when collections of atoms emitted from objects impinge upon the senses. Sensible qualities, such as colors and tastes, are said to exist only by convention, but in reality there exist only the atoms and the void. Knowledge gained through sense experience is obscure, whereas genuine knowledge is the understanding of the atomic theory, which comes solely through reason.
Epicurus adopted the atomic theory, and the exposition of it by his follower Lucretius in his poem De rerum natura (On the Nature of Things) had a marked influence on the development of modern science and philosophy.