from what the geometer had himself placed into the figure, according to concepts a priori, and then represented by a construction. All the safe a priori knowledge he had of the figure was limited to the necessary consequences of what he had himself introduced into it, in accordance with his own concept. The truths of mathematics are given by the mind, not extracted from things. And precisely in the same way, though not until the beginning of the modern period, did physics enter on the highway of science. Galilei, Torricelli, and Stahl saw that reason has insight into that only which she produces on her own plan, and that she must compel nature to answer her questions. Reason, it is true, must be taught of nature; but not in the character of a pupil, who agrees to everything the master likes, but as a judge who compels the witness to answer the questions which he himself proposes. And so, concludes Kant, even physics owes its beneficent revolution to the happy idea of seeking from nature information in accordance with what reason had itself placed into nature, though this could not be known from reason itself and must be learned from nature. The examples of mathematics and physics suggest a similar revolution for metaphysics, which, like them, is a science of rational cognitions. If these have become perfect sciences by the discovery that the truths they assert of objects are mind-originated, the same assumption might be made of metaphysics generally. And this is Kant's Copernican thought. "Hitherto it has been supposed that all our knowledge must conform to the objects: but, under that supposition, all attempts to establish anything about them a priori, by means of concepts, and thus to enlarge our knowledge, have come to nothing. The experiment, therefore, ought to be made, whether we should not succeed better with the problems of metaphysics, by assuming that the objects must conform to our mode of cognition; for this would better agree with the demanded possibility of an a priori knowledge of them, which is to settle something about objects, before they are given us."[1]
- ↑ III, 17-18 (I, 370).
