The concluding paragraph is a restatement of the argument of the Aesthetic and of § 13, Note i. of the Prolegomena. Appearances are not things in themselves. They are conditioned by the pure intuitional forms, and are therefore subject to pure mathematics “in all its precision.” Were we compelled to regard the objects of the senses as things in themselves, an applied science of geometry (again taken, in Kant’s habitual manner, as typically representing the mathematical disciplines) would not be possible. The only new element in the argument is the reference to synthesis as presupposed in all apprehension.
The additional proof with which in the second edition Kant prefaces the entire argument calls for no special comment. It may, however, be noted that though in the argument of the first edition the need of synthesis in all apprehension is clearly taught, the term synthesis is not itself employed except in the central and final paragraphs. In the proof given in the second edition both the term and what it stands for are allowed due prominence.
2. THE ANTICIPATIONS OF PERCEPTION
In all appearances sensation and the real which corresponds to it in the object (realitas phaenomenon) has an intensive magnitude or degree. Or as in the second edition: In all appearances the real, which is an object of sensation, has intensive magnitude or degree.
We may first analyse the total section. The first paragraph[1147] explains the term anticipation. The second and third paragraphs give a first proof of the principle. Paragraphs four to ten treat of continuity in space, time and change, and of the impossibility of empty space, and also afford Kant the opportunity to develop his dynamical theory of matter, and so to indicate the contribution which transcendental philosophy is able to make towards a more adequate understanding of the principles of physical science. The eleventh and twelfth paragraphs, evidently later interpolations, give a second proof of the principle which in one important respect varies from the first proof. In the second edition a third proof akin to this second proof, but carrying it a stage further, is added in the form of a new first paragraph.
Kant’s reason for changing the formulation of the principle in the second edition is evidently the unsatisfactoriness of the phrase “sensation and the real.”[1148] The principle, properly interpreted, applies not, as the first edition title and also the second proof would lead us to expect, to sensation itself, but to its object, realitas phaenomenon. It is phenomenalist in its teaching. The emphatic term “anticipation” is adopted by Kant to mark that in this principle we are able in a priori fashion to determine something in regard to what in itself is purely empirical. Sensation as such, being the matter of experience, can never be known a priori. Its quality, as being a colour or a taste, depends upon factors which are for us, owing to the limitations of our knowledge, wholly contingent. None the less in one particular respect we can predetermine the object of all sensation, and so can anticipate experience, even in its material aspect.
The first proof is as follows. Apprehension, so far as it takes place through a sensation, occupies only a single moment; it does not involve any successive synthesis proceeding from parts to the complete representation. That which is apprehended cannot, therefore, possess extensive magnitude. But, as already stated in the chapter on Schematism, reality is that in appearance which corresponds to a sensation. It is realitas phaenomenon. The absence of it is negation = 0. Now every sensation is capable of diminution; between reality in the appearance and negation there is a continuous series of many possible intermediate sensations, the difference between any two of which is always smaller than the difference between the given sensation and zero. That is to say, the real in appearance has intensive magnitude or degree. The argument is from capability of variation in the intensity of sensation to existence of degree in its object or cause. For the most part this reality is spoken of as that which is apprehended in sensation, but Kant adds that if it be
“...viewed as cause either of sensation or of other reality in appearance, such as change, the degree of its reality ... is then entitled a moment, as for instance the moment of gravity.”
The obscurity of what in itself is a very simple and direct argument would seem to be traceable to the lack of clearness in Kant’s own mind as to what is to be signified by reality. The implied distinction between sensation and its object has not been clearly formulated. Definitions have, indeed, been given of reality in the chapter on Schematism;[1149] but they are extremely difficult to decipher. Kant never varies from the assertion that reality is “that which corresponds to sensation in general.” Our difficulty is with the additional qualifications. This reality, he further declares, is
“...that, the concept of which in itself points to an existence [Sein] in time.”[1150]