Against this presupposition, for which they can have no ground in experience and which is therefore merely metaphysical, I oppose a transcendental proof, which, to be sure, will not explain the variation in the filling of space, but which still will entirely obviate the alleged necessity of the presupposition that the difference in question cannot be explained except by the as sumption of empty spaces, and which has the merit of at least granting the understanding the freedom also to think of this difference in another way, if the explanation of nature should make some hypothesis necessary for this end.