From Chapter VIII., The Younger Eleatics

167. Reality Spatially Infinite
Melissos did indeed differ from Parmenides in holding that reality was spatially as well as temporally infinite; but he gave an excellent reason for this belief, and had no need to support it by such an extraordinary argument. What he said was that, if it were limited, it would be limited by empty space. This we know from Aristotle himself,⁵⁸ and it marks a real advance upon Parmenides. He had thought it possible to regard reality as a finite sphere, but it would have been difficult for him to work out this view in detail. He would have had to say there was nothing outside the sphere; but no one knew better than he that there is no such thing as nothing. Melissos saw that you cannot imagine a finite sphere without regarding it as surrounded by an infinite empty space;⁵⁹ and as, in common with the rest of the school, he denied the void (fr. 7), he was forced to say reality was spatially infinite (fr. 3). It is possible that he was influenced in this by his association with the Ionic school.

From the infinity of reality, it follows that it must be one; for, if it were not one, it would be bounded by something else (fr. 5). And, being one, it must be homogeneous throughout (fr. 6a), for that is what we mean by one. Reality, then, is a single, homogeneous, corporeal plenum, stretching out to infinity in space, and going backwards and forwards to infinity in time.

58. Arist. Gen. Corr. A, 8. 325 a 14, ἓν καὶ ἀκίνητον τὸ πᾶν εἶναί φασι καὶ ἄπειρον ἔνιοι· τὸ γὰρ πέρας περαίνειν ἂν πρὸς τὸ κενόν.. That this refers to Mehssos has been shown by Zeller (p. 612, n. 2).

59. Note the disagreement with Zeno (§ 162).