But to state it tersely: what is really the Science of Knowledge in two words? It is this: Reason is absolutely self-determined; Reason is only for Reason; but for Reason there is also nothing but Reason. Hence, everything, which Reason is, must be grounded in itself, and out of itself, but not in or out of another—some external other, which it could never grasp without giving up itself. In short, the Science of Knowledge is transcendental idealism. Again, what is the content of the Kantian system in two words? I confess that I cannot conceive it possible how any one can understand even one sentence of Kant, and harmonize it with others, except on the same presupposition which the Science of Knowledge has just asserted. I believe that that presupposition is the everlasting refrain of his system; and I confess that one of the reasons why I refused to prove the agreement of the Science of Knowledge with Kant’s system was this: It appeared to me somewhat too ridiculous and too tedious to show up the forest by pointing out the several trees in it. I will cite here one chief passage from Kant. He says: “The highest principle of the possibility of all contemplation in relation to the understanding is this: that all the manifold be subject to the conditions of the original unity of apperception.” That is to say, in other words, “That something which is contemplated be also _thought_, is only possible on condition that the possibility of the original unity of apperception can coexist with it.” Now since, according to Kant, contemplation also is possible only on condition that it be thought and comprehended—otherwise it would remain blind—and since contemplation itself is thus subject to the conditions of the possibility of thinking—it follows that, according to Kant, not only Thinking immediately, but by the mediation of thinking, contemplation also, and hence _all consciousness_, is subject to the conditions of the original unity of apperception. Now, what is this condition? It is true, Kant speaks of conditions, but he states only one as a fundamental condition. What is this condition of the original unity of apperception? It is this (see § 16 of the _Critique of Pure Reason_), “that my representations _can_ be accompanied by the ‘_I_ think’”—the word “_I_” alone is italicised by Kant, and this is somewhat important; that is to say, _I am the thinking_ in this thinking.