This method Parmenides carries out with the utmost rigour. He will not have us pretend that we think what we must admit to be unthinkable. It is true that if we resolve to allow nothing but what we can understand, we come into direct conflict with the evidence of our senses, which present us with a world of change and decay. So much the worse for the senses, says Parmenides. To many this will doubtless seem a mistake on his part, but let us see what history has to say on the point. The theory of Parmenides is the inevitable outcome of a corporeal monism, and his bold declaration of it ought to have destroyed that theory for ever. If he had lacked courage to work out the prevailing views of his time to their logical conclusion, and to accept that conclusion, however paradoxical it might seem to be, men might have gone on in the endless circle of opposition, rarefaction and condensation, one and many, for ever. It was the thorough-going dialectic of Parmenides that made progress possible. Philosophy must now cease to be monistic or cease to be corporealist. It could not cease to be corporealist; for the incorporeal was still unknown. It therefore ceased to be monistic, and arrived at the atomic theory, which, so far as we know, is the last word of the view that the world is matter in motion. Having worked out its problems on those conditions, philosophy next attacked them on the other side. It ceased to be corporealist, and found it possible to be monistic once more, at least for a time. This progress would have been impossible but for that faith in reason which gave Parmenides the courage to reject as untrue what was to him unthinkable, however strange the result might be. [Sidenote: The results.] 88. He goes on to develop all the consequences of the admission that _it is_. It must be uncreated and indestructible. It cannot have arisen out of nothing; for there is no such thing as nothing. Nor can it have arisen from something; for there is no room for anything but itself. What is cannot have beside it any empty space in which something else might arise; for empty space is nothing, nothing cannot be thought, and therefore cannot exist. What is, never came into being, nor is anything going to come into being in the future. “Is it or is it not?” If it is, then it is now, all at once. That Parmenides was really denying the existence of empty space was quite well known to Plato. He says that Parmenides held “all things were one, and that the one remains at rest in itself, _having no place in which to move_.”[452] Aristotle is no less clear. In the _de Caelo_ he lays it down that Parmenides was driven to take up the position that the One was immovable just because no one had yet imagined that there was any reality other than sensible reality.[453] Footnote 452: Plato, _Tht._ 180 e 3, ὡς ἕν τε πάντα ἐστὶ καὶ ἕστηκεν αὐτὸ ἐν αὐτῷ οὐκ ἔχον χώραν ἐν ᾗ κινεῖται. Footnote 453: