Stamp issued by Greece on Sept. 26, 1983, to honor an International Conference on Democritus and his work
Democritus was a pre-Socratic Greek philosopher (born at Abdera in Thrace around 460 BC; lived to be very old, but died at an unknown date). Democritus was a student of Leucippus, and co-originator of the belief that all matter is made up of various imperishable indivisible elements which he called atoms. It is virtually impossible to tell which of these ideas were unique to Democritus, and which are attributable to Leucippus. Democritus is also the first philosopher we know who realized that what we perceive as the Milky Way is the light of distant stars. Other philosophers, including later Aristotle, argued against this. Democritus was among the first to propose that the universe contains many worlds, some of them inhabited:
He was also a pioneer of mathematics and geometry in particular. We only know this through citations of his works (titled On Numbers, On Geometrics, On Tangencies, On Mapping, and On Irrationals) in other writings, since most of Democritus' body of work did not survive the Middle Ages. Aristotle tells us that his theory of matter, commonly called atomism[?], was a reaction to Parmenides, who denied the existence of motion, change, or the void. Parmenides argued that the existence of a thing implied that it could not have "come into being", because "nothing comes from nothing[?]". Moreover, he argued, movement was impossible, because one must move into "the void" and (as he identified "the void" with "nothing") the void does not exist and cannot be "moved into".
Democritus agreed that everything which is must be eternal, but denied that "the void" can be equated with nothing. This makes him the first thinker on record to argue for the existence of an entirely empty "void". In order to explain the change around us from basic, unchangeable substance he argued that there are various basic elements which always existed but can be rearranged into many different forms. He argued that atoms only had several properties, particularly size, shape, and mass; all other properties that we attribute to matter, such as color and taste, are but the result of complex interactions between the atoms in our bodies and the atoms of the matter that we are examining. Furthermore, he believed that the real properties of atoms determine the perceived properties of matter--for example, something that tastes sharp is made of small, pointy atoms, while something sweet is made of large, round atoms; the interactions of those atoms with the atoms of the tongue give the impression of taste. Some types of matter are particularly solid because their atoms have hooks to attach to each other; some are oily because they are made of very fine, small atoms which can easily slip past each other. In Democritus' own words, "By convention sweet, by convention bitter, by convention hot, by convention cold, by convention colour: but in reality atoms and void."