:This article is about the philosopher. There was also a Greek mythological Leucippus (mythology). A genus of hummingbirds also is named Leucippus. Leucippus or Leukippos (Greek: , first half of 5th century BC) was among the earliest philosophers of atomism, the idea that everything is composed entirely of various imperishable, indivisible elements called atoms. He was born at Miletus or Abdera

There are no existing writings which we can attribute to Leucippus, since his writings seem to have been folded into the work of his famous student Democritus (q.v. for more on atomism). In fact, it is virtually impossible to identify any views about which Democritus and Leucippus disagreed.

Leucippus was a contemporary of Zeno, Empedocles and Anaxagoras of the Ionian school of philosophy. Leucippus was most influenced by Zeno, who possessed a great interest in the problems and paradoxes of space. He studied at the school in Elea, but it is not certain whether this was before or after the death of Parmenides. Around 440 B.C. or 430 B.C. Leucippus founded a school at Abdera, which his pupil, Democritus, was closely associated with. His fame was so completely overshadowed by that of Democritus, who systematized his views on atoms, that Epicurus doubted his very existence, according to Diogenes Laertius x. 7.

However Aristotle and Theophrastus explicitly credit Leucippus with the invention of Atomism. Leucippus agreed with the Eleatic argument that true being does not admit of vacuum. And there can be no movement in the absence of vacuum. Leucippus contended that since movement exists, there has to be vacuum. However, he concludes that vacuum is identified with non-being, since it cannot really be. Leucippus differed from the Eleatics in not being encumbered by the conceptual intermingling of being and non-being. Plato made the necessary distinction between grades of being and types of negation.

The most famous among Leucippus' lost works were titled Megas Diakosmos (The Great Order of the Universe or The great world-system) and Peri Nou (On mind).

A single fragment of Leucippus survives:

A.A. Long (ed.), The Cambridge Companion to Early Greek Philosophy (pgs. xxiii, 185)

Diels-Kranz, Die Fragmente der Vorsokratiker [I] 67A

Diogenes Laertius, Diogenes Lartius: Lives of Eminent Philosophers, IX.30-33

* Stanford Encyclopedia of Philosophy entry