There are a number of points in the deduction of the first edition which call for further explanatory and critical comment. The first of these concerns the somewhat misleading character of the term _a priori_ as applied to the categories. It carries with it rationalistic associations to which the Critical standpoint, properly understood, yields no support. The categories are for Kant of merely _de facto_ nature. They have no intrinsic validity. They are proved only as being the indispensable conditions of what is before the mind as brute fact, namely, conscious experience. By the _a priori_ is meant merely those _relational_ factors which are required to supplement the given manifold in order to constitute our actual consciousness. And, as Kant is careful to point out, the experience, as conditions of which their validity is thus established, is of a highly specific character, resting upon synthesis of a manifold given in space and time. That is to say, their indispensableness is proved only for a consciousness which in these fundamental respects is constituted like our own.[904] And secondly, the validity of the _a priori_ categories, even in our human thinking, is established only in reference to that empirical world which is constructed out of the given manifold in terms of the intuitive forms, space and time. Their validity is a merely phenomenal validity. They are valid of appearances, but not of things in themselves. The _a priori_ is thus doubly _de facto_: first as a condition of brute fact, namely, the actuality of our human consciousness; and secondly, as conditioning a consciousness whose knowledge is limited to appearances. It is a relative, not an absolute _a priori_. Acceptance of it does not, therefore, commit us to rationalism in the ordinary meaning of that term. Its credentials are conferred upon it by what is mere fact; it does not represent an order superior to the actual and legislative for it. In other words, it is Critical, not Leibnizian in character. No transcendent metaphysics can be based upon it. In formulating this doctrine of the _a priori_ as yielding objective insight and yet as limited in the sphere of its application, the _Critique of Pure Reason_ marks an epoch in the history of scepticism, no less than in the development of Idealist teaching.