The relation between the thing in itself and the phenomenon is also variable. Now they are regarded as entirely heterogeneous (that which can never be intuited exists in a mode opposed to that of the intuited and intuitable), and now as analogous to each other (non-intuitable properties of the thing in itself correspond to the intuitable characteristics of the phenomenon). The former is the case when it is said that phenomena are in space and time, while things in themselves are not; that in the first of these classes natural causation rules, and in the second freedom; that in the one-conditioned existence alone is found, in the other unconditioned.[1] But just as often things in themselves and phenomena are conceived as similar to one another, as two sides of the same object,[2] of which one, like the counter-earth of the Pythagoreans, always remains turned away from us, while the other is turned toward us, but does not reveal the true being of the object. According to this each particular thing, state, relation, and event in the world of phenomena would have its real counterpart in the noumenal sphere: un-extended roses in themselves would lie back of extended roses, certain non-temporal processes back of their growth and decay, intelligible relations back of their relations in space. This is approximately the relation of the two conceptions as in part taught by Lotze himself, in part represented by him as taught by Kant. Herbart's principle, "So much seeming, so much indication of being" (wie viel Schein so viel Hindeutung aufs Sein), might also be cited in this connection. That which continually impelled Kant, in spite of his proclamation of the unknowableness of things in themselves, to form ideas about their character, was the moral interest, but this sometimes threw its influence in favor of their commensurability with phenomena and sometimes in the opposite scale. For in his ethics Kant needs the intelligible character or man as noumenon, and must assume as many men in themselves (to be consistent, then, in general, as many beings in themselves) as there are in the world of phenomena. But for practical reasons, again, the causality of the man in himself must be thought of as entirely different from, and opposed to, the mechanical causality of the sense world. Kant's judgment is, also, no more stable concerning the value of the knowledge of the suprasensible, which is denied to us. "I do not need to know what things in themselves may be, because a thing can never be presented to me otherwise than as a phenomenon." And yet a natural and ineradicable need of the reason to obtain some conviction in regard to the other world is said to underlie the abortive attempts of metaphysics; and Kant himself uses all his efforts to secure to the practical reason the satisfaction of this need, though he has denied it to the speculative reason, and to make good the gap in knowledge by faith. From the theoretical standpoint an extension of knowledge beyond the limits of phenomena appears impossible, but unnecessary; from the practical standpoint it is, to a certain extent, possible and indispensable.

[Footnote 1: Kant's conjectures concerning a common ground of material and mental phenomena, and those concerning the common root of sensibility and understanding, show the same tendency. On the one hand, duality, on the other, unity.]

[Footnote 2: "Phenomenon, which always has two sides, the one when the object in itself is considered (apart from the way in which it is intuited, and just because of which fact its character always remains problematical), the other when we regard the form of the intuition of this object, which must be sought not in the object in itself, but in the subject to whom the object appears, while it nevertheless actually and necessarily belongs to the phenomenon of this object." "This predicate "—sc., spatial quality, extension—"is attributed to things only in so far as they appear to us.">[

There is, then, a threefold distinction to be made: (1) Things in themselves, which can never be the object of our knowledge, because our forms of intuition are not valid for them. (2) Phenomena, things for us, nature or the totality of that which either is or, at least, may be the object of our knowledge (here belong the possible inhabitants of the moon, the magnetic matter which pervades all bodies, and the forces of attraction and repulsion, though the first have never been observed, and the second is not perceptible on account of the coarseness of our senses, and the last, because forces in general are not perceptible; nature comprehends everything whose existence "is connected with our perceptions in a possible experience"[1]). (3) Our representations of phenomena, i.e., that of the latter which actually enters into the consciousness of the empirical individual. In the realm of things in themselves there is no motion whatever, but at most an intelligible correlate of this relation; in the world of phenomena, the world of physics, the earth moves around the sun; in the sphere of representation the sun moves around the earth. It is true, as has been said, that Kant sometimes ignores the distinction between phenomena as related to noumena and phenomena as related to representations; and, as a result of this, that the phenomenon is either completely volatilized into the representation[2] or split up into an objective half independent of us and a representative half dependent on us, of which the former falls into the thing in itself,[3] while the latter is resolved into subjective states of the ego.

[Footnote 1: "Nothing is actually given to us but the perception and the empirical progress from this to other possible perceptions." "To call a phenomenon a real thing antecedent to perception, means … that in the progress of experience we must meet with such a perception.">[

[Footnote 2: Phenomena "are altogether in me," "exist only in our sensibility as a modification of it." "There is nothing in space but that which is actually represented in it." Phenomena are "mere representations, which, if they are not given in us (in perception) nowhere exist.">[

[Footnote 3: Here Kant is guilty of the fault which he himself has censured, of confusing the physical and transcendental meanings of "in itself." He forgets that the thing, if it is momentarily not intuited or represented by me, and therefore is not immediately given for me as an individual, is nevertheless still present for me as man, is mediately given, that is, is discoverable by future search. That which is without my present consciousness is not for this reason without all human consciousness. In fact, Kant often overlooks the distinction between actual and possible intuition, so that for him the "objects" of the latter slip out of space and time and into the thing in itself. To the "transcendental object we may ascribe the extent and connection of our possible perceptions, and say that it is given in itself before all experience." In it "the real things of the past are given.">[

After the possibility and the legitimacy of synthetic judgments a priori have been proved for pure mathematics upon the basis of the pure intuitions, there emerges, in the second place, the problem of the possibility of a priori syntheses in pure natural science, or the question, Do pure concepts exist? And after this has been answered in the affirmative, the further questions come up, Is the application of these, first, to phenomena, and second, to things in themselves, possible and legitimate, and how far?

%(b) The Concepts and Principles of the Pure Understanding (Transcendental Analytic).%—Sensations, in order to become "intuition" or the perception of a phenomenon, needed to be ordered in space and time; in order to become "experience" or a unified knowledge of objects, intuitions need a synthesis through concepts. In order to objective knowledge the manifold of intuition (already ordered by its arrangement in space and time) must be connected in the unity of the concept. Sensibility gives the manifold to be connected, the understanding the connecting unity. The former is able to intuit only, the latter only to think; knowledge can arise only as the result of their union. Intuitions depend on affections, concepts on functions, that is, on unifying acts of the understanding.

To discover the pure forms of thought it is necessary to isolate the understanding, just as an isolation of the sensibility was necessary above in order to the discovery of the pure forms of intuition. We obtain the elements of the pure knowledge of the understanding by rejecting all that is intuitive and empirical. These elements must be pure, must be concepts, further, not derivative or composite, but fundamental concepts, and their number must be complete. This completeness is guaranteed only when the pure concepts or categories are sought according to some common principle, which assigns to each its position in the connection of the whole, and not (as with Aristotle) collected by occasional, unsystematic inquiries undertaken at random. The table of the forms of judgment will serve as a guide for the discovery of the categories. Thought is knowledge through concepts; the understanding can make no other use of concepts than to judge by means of them. Hence, since the understanding is the faculty of judging, the various kinds of connection in judgment must yield the various pure "connective-concepts" (Verknüpfungsbegriffe.—K. Fischer) or categories.