From Chapter IX., Leukippos of Miletos
Leukippos affirmed the existence both of the Full and the Empty, terms which he may have
borrowed from Melissos.24 He had to assume 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.
24. Arist. Met. A, 4. 985 b 4 (R. P. 192). Cf. Melissos, fr. 7 sub fin.