First of all we shall present to ourselves clearly and examine the fundamental thought in which the aim of the whole “Critique of Pure Reason” lies. Kant placed himself at the standpoint of his predecessors, the dogmatic philosophers, and accordingly he started with them from the following assumptions:—(1.) Metaphysics is the science of that which lies beyond the possibility of all experience. (2.) Such a science can never be attained by applying principles which must first themselves be drawn from experience (_Prolegomena_, § 1); but only what we know _before_, and thus _independently of_ all experience, can reach further than possible experience. (3.) In our reason certain principles of this kind are actually to be found: they are comprehended under the name of Knowledge of pure reason. So far Kant goes with his predecessors, but here he separates from them. They say: “These principles, or this knowledge of pure reason, are expressions of the absolute possibility of things, _æternæ veritates_, sources of ontology; they stand above the system of the world, as fate stood above the gods of the ancients.” Kant says, they are mere forms of our intellect, laws, not of the existence of things, but of our idea of them; they are therefore valid merely for our apprehension of things, and hence they cannot extend beyond the possibility of experience, which, according to assumption 1, is what was aimed at; for the _a priori_ nature of these forms of knowledge, since it can only rest on their subjective origin, is just what cuts us off for ever from the knowledge of the nature of things in themselves, and confines us to a world of mere phenomena, so that we cannot know things as they may be in themselves, even _a posteriori_, not to speak of _a priori_. Accordingly metaphysics is impossible, and criticism of pure reason takes its place. As opposed to the old dogmatism, Kant is here completely victorious; therefore all dogmatic attempts which have since appeared have been obliged to pursue an entirely different path from the earlier systems; and I shall now go on to the justification of my own system, according to the expressed intention of this criticism. A more careful examination, then, of the reasoning given above will oblige one to confess that its first fundamental assumption is a _petitio principii_. It lies in the proposition (stated with particular clearness in the _Prolegomena_, § 1): “The source of metaphysics must throughout be non-empirical; its fundamental principles and conceptions must never be taken from either inner or outer experience.” Yet absolutely nothing is advanced in proof of this cardinal assertion except the etymological argument from the word metaphysic. In truth, however, the matter stands thus: The world and our own existence presents itself to us necessarily as a riddle. It is now assumed, without more ado, that the solution of this riddle cannot be arrived at from a