175. Leukippos affirmed the existence both of the Full and the Empty, terms which he may have borrowed from Melissos.[946] As we have seen, he had to assume the existence of empty space, which the Eleatics had denied, in order to make his explanation of the nature of body possible. Here again he is developing a Pythagorean view. The Pythagoreans had spoken of the void, which kept the units apart; but they had not distinguished it from atmospheric air (§ 53), which Empedokles had shown to be a corporeal substance (§ 107). Parmenides, indeed, had formed a clearer conception of space, but only to deny its reality. Leukippos started from this. He admitted, indeed, that space was not real, that is to say, corporeal; but he maintained that it existed all the same. He hardly, it is true, had words to express his discovery in; for the verb “to be” had hitherto been used by philosophers only of body. But he did his best to make his meaning clear by saying that “what is not” (in the old corporealist sense) “is” (in another sense) just as much as “what is.” The void is as real as body. Footnote 946: Arist. _Met._ Α, 4. 985 b 4 (R. P. 192). Cf. Melissos, fr. 7 _sub fin._ It is a curious fact that the Atomists, who are commonly regarded as the great materialists of antiquity, were actually the first to say distinctly that a thing might be real without being a body. [Sidenote: Cosmology.] 176. It might seem a hopeless task to disentangle the cosmology of Leukippos from that of Demokritos, with which it is generally identified; but that very fact affords an invaluable clue. So far as we know, no one after Theophrastos was able to distinguish the doctrines of the two men, and it follows from this that all definite statements about Leukippos in later writers must, in the long run, go back to him. If we follow this up, we shall be able to give a fairly clear account of the system, and we shall even come across some views which are peculiar to Leukippos and were not adopted by Demokritos.[947] Footnote 947: Cf. Zeller, “Zu Leukippus” (_Arch._ xv. p. 138). We shall start from the fuller of the two doxographies in Diogenes, which comes from an epitome of Theophrastos.[948] It is as follows:—