B. 460–457 bc,
40 years after Anaxagoras acc. to his own statement quoted by Diogenes (4) Laertius. He travelled widely, acc. to various later accounts, and lived to a great age. In time he became known as ‘the laughing philosopher’, probably because he held that ‘cheerfulness’ was a goal to be pursued in life. There is a story that he visited Athens—‘but no one knew me’; this may be a reflection of the undoubted fact that Plato, although he must have known his work, never mentioned him by name.
Diog. Laert. mentions 70 titles, classified as follows: Ethics, Physics, Unclassified, Mathematics, Music (which includes philological and literary criticism), Technical, and Notes. None of these works survives. Of his physical theories, on which his fame rests, only meagre quotations and summaries remain; most of the texts that have come down to us under his name are brief and undistinguished moral maxims.
From the time of Aristotle, Democritus and Leucippus are jointly credited with the creation of the atomic theory of the universe (see atomism); it is now impossible to distinguish the contribution of each. Aristotle's account of the origin of the theory rightly relates it to the Eleatic School. Parmenides had argued that what is real is one and motionless, since empty space is not a real existent; motion is impossible without empty space, and plurality is impossible without something to separate the units. Division of what is real into units in contact, i.e. with no separating spaces, is ruled out because (a) infinite divisibility would mean there are no real units at all, and (b) finite divisibility is physically inexplicable. Against these arguments, says Aristotle, Leucippus proposed to rescue the sensible world of plurality and motion by asserting that empty space, ‘the non‐existent’, may nevertheless serve to separate parts of what exists from each other. So the universe has two ingredients: Being, which satisfies the Eleatic criteria by being ‘full’, unchanging, and homogeneous, and Non‐being or empty space. The pieces of real Being, since it is their characteristic to be absolutely indivisible units, are called ‘atoms’ (lit. ‘uncuttables’). They are said to be solid, invisibly small, and undifferentiated in material; they differ from each other in shape and size only (perhaps also in weight), and the only change they undergo is in their relative and absolute position, through movement in space.
By their changes of position the atoms produce the compounds of the changing sensible world. Compounds differ in quality according to the shape and arrangement of the component atoms, their congruence or otherwise (i.e. their tendency to latch together because of their shape), and the amount of space between them. It is a matter of controversy whether the atoms have a natural downward motion due to weight (as later in Epicurean theory: see epicurus, Doctrines ) or move randomly in the void until their motion is somehow directed by collisions with other atoms. In the course of time, groups of atoms form ‘whirls’ or vortices, which have the effect of sorting out the atoms by size and shape, like to like. Some of these are sorted in such a way as to produce distinct masses having the appearance of earth, water, air, and fire: thus worlds are formed—not one single world, as in most Greek cosmologies, but an indeterminate number scattered thoughout the infinite void, each liable to perish through random atomic motions, as they were originally formed. Leucippus and Democritus produced an account of the evolution within worlds of progressively more complex stages of organization, including human cultures.
Subjects: Classical Studies.