an excellent test of the new method of thought which we have adopted, and which is based on the principle that we only cognize in things _à priori_ that which we ourselves place in them.[4] [4] This method, accordingly, which we have borrowed from the natural philosopher, consists in seeking for the elements of pure reason in that _which admits of confirmation or refutation by experiment_. Now the propositions of pure reason, especially when they transcend the limits of possible experience, do not admit of our making any experiment with their _objects_, as in natural science. Hence, with regard to those _conceptions_ and _principles_ which we assume _à priori_, our only course will be to view them from two different sides. We must regard one and the same conception, _on the one hand_, in relation to experience as an object of the senses and of the understanding, _on the other hand_, in relation to reason, isolated and transcending the limits of experience, as an object of mere thought. Now if we find that, when we regard things from this double point of view, the result is in harmony with the principle of pure reason, but that, when we regard them from a single point of view, reason is involved in self-contradiction, then the experiment will establish the correctness of this distinction. This attempt succeeds as well as we could desire, and promises to metaphysics, in its first part—that is, where it is occupied with conceptions _à priori_, of which the corresponding objects may be given in experience—the certain course of science. For by this new method we are enabled perfectly to explain the possibility of _à priori_ cognition, and, what is more, to demonstrate satisfactorily the laws which lie _à priori_ at the foundation of nature, as the sum of the objects of experience—neither of which was possible according to the procedure hitherto followed. But from this deduction of the faculty of _à priori_ cognition in the first part of metaphysics, we derive a surprising result, and one which, to all appearance, militates against the great end of metaphysics, as treated in the second part. For we come to the conclusion that our faculty of cognition is unable to transcend the limits of possible experience; and yet this is precisely the most essential object of this science. The estimate of our rational cognition _à priori_ at which we arrive is that it has only to do with phenomena, and that things in themselves, while possessing a real existence, lie beyond its sphere. Here we are enabled to put the justice of this estimate to the test. For that which of necessity impels us to transcend the limits of experience and of all phenomena is the _unconditioned_, which reason absolutely requires in things as they are in themselves, in order to complete the series of conditions. Now, if it appears that when, on the one hand, we assume that our cognition conforms to its objects as things in themselves, _the unconditioned