are, but only of objects as they appear to us in the forms of space, time, and the categories. Things themselves, however, though we can never know them, or even that they exist, we must continue to think as real counterparts to the phenomenal objects of our knowledge. Otherwise we should have the absurd result of an appearance without anything that appeared. And in this way the door of the suprasensible world, with its transcendent objects – God, Freedom, and Immortality – is left open to faith.
Some passages in the second preface, which was written in view of criticisms on the entire work as it appeared in the first edition, may not be intelligible at this stage to readers unacquainted with the general subject-matter of the book. But even to them Kant's aim and problem must stand out with perfect clearness. His object is to make an inventory of the possessions of pure reason, to fix the limits of its use, and to explain why, within a certain area, though not beyond, it gives us an objectively valid knowledge of things. It is in addressing himself to the last part of this entire undertaking that Kant comes upon the Copernican thought with which he would revolutionize metaphysics, and transform it, as geometry and physics had been similarly transformed, into an irrefragable science. If the inkling of his solution which we have just given seems obscure, it may be illuminated and expanded in another article. Here it concerns us to realize, not the solution, but the problem itself. This is to survey, explain, and (indirectly) vindicate a priori knowledge, and to distinguish it from its counterfeit semblance. If the undertaking is successfully carried out, there will emerge, in Kant's opinion, a science absolutely complete and perfect for all time, the science of pure reason. For he holds that reason, so far as its principles of knowledge are concerned, forms a separate and independent unity, in which, as in an organic body, every member exists for the sake of all others, and all others for it, so that no principle can be safely applied in one relation unless it has been carefully examined in all its relations to the whole employment of pure reason. Thus the Critique can claim to have
