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There is practically nothing known about the life of Leucippus and his book appears to have been incorporated into the collective works of Democritus. No writer subsequent to Theophrastos seems to have been able to distinguish his teachings from that of his more famous disciple. Indeed his very existence has been denied, though on insufficient grounds particularly as Aristotle gives a clear account as to how Leucippus's theory arose.
Leucippus, in opposition to Parmenides' denial of the void, proposes the atomic theory, which supposes that everything in the universe is either atoms or voids; a theory which, according to Aristotle, was stimulated into conception so to purposely contradict Parmenides' argument.
He admitted that there could be no motion if there was no void and he inferred that it was wrong to identify the void with the non-existent. Leucippus rectified the Pythagorean theory of air inhabiting space with the notion of a vacuum.
Weight for the early atomists is only a secondary phenomena, rising in a manner to be explained from excess of magnitude. It will be observed that in this respect, the early atomists, who were far more scientific than Aristotle or Epicurus. Leucippus explained the phenomena of weight from the size of the atoms and their combustions, but did not regard weight itself as the primary property of bodies. However, Aristotle distinctly claimed that none of his predecessors ascribed weight to the atom which is clearly unprovable and Plato expressly rejected this claim.
The solitary fragment of Leucippus that we possess is to the effect that, "Naught happens for nothing, but all things from a ground (logos) and of necessity." Some suppose that this implies that 'nothing is random'.
