The reader is probably acquainted with Kant’s dictum that the understanding makes nature. It gives no doubt a somewhat startling expression to the revolution in philosophy which Kant believed himself to have introduced, and which he compared to the Copernican theory in men’s conception of the relative positions of the earth and the sun. When we enquire, however, into the precise sense in which Kant used the expression, we find that its meaning is subject to a qualification which testifies to the difficulty experienced by Kant himself in carrying out the doctrine which the words seemed to convey. Macht zwar der Verstand die Natur, aber er schafft sie nicht. The understanding makes nature, but out of a material which it does not make. That material, according to Kant, consists in phenomena or data of sensibility, given under the so-called forms of intuition, space and time. This apparent ascription of nature to a twofold origin—an origin in understanding in respect of its form as a nature, as a single system of experience; an origin elsewhere in respect of the matter which through the action of understanding becomes a nature—cannot but strike us as unsatisfactory. Perhaps it may not be a doctrine in which we can permanently acquiesce, but meanwhile it represents fairly enough on its two sides the considerations which on the one hand lead us to regard nature as existing only in relation to thought, and those on the other which seem obstinately opposed to such a view. (§ 11 ¶ 1)