Leucippus

Leucippus, of Miletus or Abdera, was the first to say that the world is made of indivisible bodies moving in an empty space — the answer of a natural philosopher to the Eleatic proof that motion and plurality are impossible. Aristotle treats him as the originator of the theory that Democritus developed, and quotes the argument that took him to it: what is must be either one and unmoved, as Parmenides held, or many, and if many there must be void between the many. One sentence of his own work survives, from the On Mind: Nothing happens at random, but everything from reason and by necessity. Epicurus was said to have denied that he ever existed.