of his individual ends. Accordingly he was bold and thoughtless enough to deny the thing in itself altogether, and to set up a system in which, not, as with Kant, the mere form of the idea, but also the matter, its whole content, was professedly deduced a priori from the subject. In doing this, he counted with perfect correctness upon the want of judgment and the stupidity of the public, which accepted miserable sophisms, mere hocus-pocus and senseless babble, for proofs; so that he succeeded in turning its attention from Kant to himself, and gave the direction to German philosophy in which it was afterwards carried further by Schelling, and ultimately reached its goal in the mad sophistry of Hegel.
I now return to the great mistake of Kant, already touched on above, that he has not properly separated perceptible and abstract knowledge, whereby an inextricable confusion has arisen which we have now to consider more closely. If he had sharply separated ideas of perception from conceptions merely thought in abstracto, he would have held these two apart, and in every case would have known with which of the two he had to do. This, however, was unfortunately not the case, although this accusation has not yet been openly made, and may thus perhaps be unexpected. His “object of experience,” of which he is constantly speaking, the proper object of the categories, is not the idea of perception; neither is it the abstract conception, but it is different from both, and yet both at once, and is a perfect chimera. For, incredible as it may seem, he lacked either the wisdom or the honesty to come to an understanding with himself about this, and to explain distinctly to himself and others whether his “object of experience, i. e., the knowledge produced by the application of the categories,” is the idea of perception in space and time (my first class of ideas), or merely the abstract conception. Strange as it is, there always runs in his mind something between the two, and hence arises the unfortunate confusion which I must now bring to light. For this end I must go through the whole theory of elements in a general way.
The “Transcendental Æsthetic” is a work of such extraordinary merit that it alone would have been sufficient to immortalise the name of Kant. Its proofs carry such perfect conviction, that I number its propositions among incontestable truths, and without doubt they are also among those that are richest in results, and are, therefore, to be regarded as the rarest thing in the world, a real and great discovery in metaphysics. The fact, strictly proved by him, that a part of our knowledge is known to us a priori, admits of no other explanation than that this constitutes the forms of our intellect; indeed, this is less an explanation than merely the distinct expression of the fact itself. For a priori means nothing else than “not gained on the path of experience, thus not come into us from without.” But what is present in the intellect, and has not come from without, is just what belongs originally to the intellect itself, its own nature. Now if what is thus present in the intellect itself consists of the general mode or manner in which it must present all its objects to itself, this is just saying that what is thus present is the intellect's forms of knowing, i. e., the mode, fixed once for all, in which it fulfils this its function. Accordingly, “knowledge a priori” and “the intellect's own forms” are at bottom only two expressions for the same things thus to a certain extent synonyms.
Therefore from the doctrine of the Transcendental Æsthetic I knew of nothing to take away, only of something to add. Kant did not carry out his thought to the end, especially in this respect, that he did not reject Euclid's whole method of demonstration, even after having said on p. 87; V. 120, that all geometrical knowledge has direct evidence from perception. It is most remarkable that one of Kant's opponents, and indeed the acutest of them, G. E. Schulze (Kritik der theoretischen Philosophie, ii. 241), draws the conclusion that from his doctrine an entirely different treatment of geometry from that which is actually in use would arise; and thus he thought to bring an apagogical argument against Kant, but, in fact, without knowing it, he only began the war against the method of Euclid. Let me refer to § 15 of the first book of this work.
After the full exposition of the universal forms of perception given in the Transcendental Æsthetic, one necessarily expects to receive some explanation as to its content, as to the way in which the empirical perception comes into our consciousness, how the knowledge of this whole world, which is for us so real and so important, arises in us. But the whole teaching of Kant contains really nothing more about this than the oft-repeated meaningless expression: “The empirical element in perception is given from without.” Consequently here also from the pure forms of perception Kant arrives with one spring at thinking at the Transcendental Logic. Just at the beginning of the Transcendental Logic (Critique of Pure Reason, p. 50; V. 74), where Kant cannot avoid touching upon the content of the empirical perception, he takes the first false step; he is guilty of the πρωτον ψευδος. “Our knowledge,” he says, “has two sources, receptivity of impressions and spontaneity of conceptions: the first is the capacity for receiving ideas, the second that of knowing an object through these ideas: through the first an object is given us, through the second it is thought.” This is false; for according to it the impression, for which alone we have mere receptivity, which thus comes from without and alone is properly “given,” would be already an idea, and indeed an object. But it is nothing more than a mere sensation in the organ of sense, and only by the application of the understanding (i. e., of the law of causality) and the forms of perception, space and time, does our intellect change this mere sensation into an idea, which now exists as an object in space and time, and cannot be distinguished from the latter (the object) except in so far as we ask after the thing in itself, but apart from this is identical with it. I have explained this point fully in the essay on the principle of sufficient reason, § 21. With this, however, the work of the understanding and of the faculty of perception is completed, and no conceptions and no thinking are required in addition; therefore the brute also has these ideas. If conceptions are added, if thinking is added, to which spontaneity may certainly be attributed, then knowledge of perception is entirely abandoned, and a completely different class of ideas comes into consciousness, non-perceptible abstract conceptions. This is the activity of the reason, which yet obtains the whole content of its thinking only from the previous perception, and the comparison of it with other perceptions and conceptions. But thus Kant brings thinking into the perception, and lays the foundation for the inextricable confusion of intuitive and abstract knowledge which I am now engaged in condemning. He allows the perception, taken by itself, to be without understanding, purely sensuous, and thus quite passive, and only through thinking (category of the understanding) does he allow an object to be apprehended: thus he brings thought into the perception. But then, again, the object of thinking is an individual real object; and in this way thinking loses its essential character of universality and abstraction, and instead of general conceptions receives individual things as its object: thus again he brings perception into thinking. From this springs the inextricable confusion referred to, and the consequences of this first false step extend over his whole theory of knowledge. Through the whole of his theory the utter confusion of the idea of perception with the abstract idea tends towards a something between the two which he expounds as the object of knowledge through the understanding and its categories, and calls this knowledge experience. It is hard to believe that Kant really figured to himself something fully determined and really distinct in this object of the understanding; I shall now prove this through the tremendous contradiction which runs through the whole Transcendental Logic, and is the real source of the obscurity in which it is involved.
In the “Critique of Pure Reason,” p. 67-69; V. 92-94; p. 89, 90; V. 122, 123; further, V. 135, 139, 153, he repeats and insists: the understanding is no faculty of perception, its knowledge is not intuitive but discursive; the understanding is the faculty of judging (p. 69; V. 94), and a judgment is indirect knowledge, an idea of an idea (p. 68; V. 93); the understanding is the faculty of thinking, and thinking is knowledge through conceptions (p. 69; V. 94); the categories of the understanding are by no means the conditions under which objects are given in perception (p. 89; V. 122), and perception in no way requires the functions of thinking (p. 91; V. 123); our understanding can only think, not perceive (V. pp. 135, 139). Further, in the “Prolegomena,” § 20, he says that perception, sensation, perceptio, belongs merely to the senses; judgment to
