We are thus furnished with all the means for forming metaphysical fundamental principles (judgments apriori); we have, firstly, conceptions apriori, and secondly, schemata through which we can apply these conceptions to objects; for since every object which we can perceive, falls in time, so must it also fall under one of these schemata, which have been borrowed from time, and must consequently permit the corresponding category to be applied to it. The judgments which we here attain are synthetical. They are, corresponding to the four classes of categories, the following: (1) All phenomena are, according to intuition, extensive greatness, since they cannot be apprehended otherwise than through space and time. On this principle the axioms of intuition rely. (2) All phenomena are, according to sensation, intensive greatness, since every sensation has a determined degree, and is capable of increase and diminution. On this principle the anticipations of perception rest. (3) The phenomena stand under necessary time-determinations. They contain the substantial, which abides, and the accidental, which changes. In reference to the change of accidence, they are subject to the law of the following connection, through the relation of cause and effect: as substances they are, in respect of their accidences, in a constant reciprocal action. From this principle spring the analogies of experience. (4) The postulates of empirical thinking are contained in the principles: (a) that which coincides with the formal conditions of experience, is possible, and can become phenomenon; (b) that which agrees with the material conditions of experience is actual, and is phenomenon; (c) that, whose connection with the actual is determined according to the universal conditions of experience, is necessary, and must be phenomenon. Such are the possible and authorized synthetical judgments apriori. But it must not be forgotten that we are entitled to make only an empirical use of all these conceptions and principles, and that we must ever apply them only to things as objects of a possible experience, and never to things in themselves; for the conception without an object is an empty form, but the object cannot be given to the conception except in intuition, and the pure intuition of space and time needs to be filled by experience. Hence, without reference to human experience, these apriori conceptions and principles are nothing but a sporting of the imagination and the understanding, with their representations. Their peculiar determination is only to enable us to spell perceptions, that we may read them as experiences. But here one is apt to fall into a delusion, which can hardly be avoided. Since the categories are not grounded upon the sensory, but have an apriori origin, it would seem as though their application would reach far beyond the sense; but such a view is a delusion; our conceptions are not able to lead us to a knowledge of things in themselves (noumena), since our intuition gives us only phenomena for the content of our conceptions, and the thing in itself can never be given in a possible experience; our knowledge remains limited to the phenomena. The source of all the confusions and errors and strife in previous metaphysics, was in confounding the phenomenal with the noumenal world.

Besides the categories or conceptions of the understanding, which have been considered, and which are especially important for experience, though often applied erroneously beyond the province of experience, there are other conceptions whose peculiar province is only to deceive; conceptions whose express determination is to pass beyond the province of experience, and which may consequently be called transcendent. These are the fundamental conceptions and principles of the previous metaphysics. To examine these conceptions, and destroy the appearance of objective science and knowledge, which they falsely exhibit, is the problem of the Transcendental Dialectics (the second part of the transcendental logic).

3. The Transcendental Dialectics.—In a strict sense, the reason is distinguished from the understanding. As the understanding has its categories, the reason has its ideas; as the understanding forms fundamental maxims from conceptions, the reason forms principles from ideas, in which the maxims of the understanding have their highest confirmation. The peculiar work of the reason is, in general, to find the unconditioned for the conditioned knowledge of the understanding, and to unify it. Hence the reason is the faculty of the unconditioned, or of principles; but since it has no immediate reference to objects, but only to the understanding and its judgments, its activity must remain an immanent one. If it would take the highest unity of the reason not simply in a transcendental sense, but exalt it to an actual object of knowledge, then it would become transcendent in that it applied the conceptions of the understanding to the knowledge of the unconditioned. From this transcending and false use of the categories, arises the transcendental appearance which decoys us beyond experience, by the delusive pretext of widening the domain of the pure understanding. It is the problem of the transcendental logic to discover this transcendental appearance.

The speculative ideas of the reason, derived from the three kinds of logical conclusion, the categorical, the hypothetical, and the disjunctive, are threefold.

(1.) The psychological idea, the idea of the soul, as a thinking substance (the object hitherto of rational psychology).

(2.) The cosmological idea, the idea of the world as including all phenomena (the object hitherto of cosmology).

(3.) The theological idea, the idea of God as the highest condition of the possibility of all things (the object hitherto of rational theology).

But with these ideas, in which the reason attempts to apply the categories of the understanding to the unconditioned, the reason becomes unavoidably entangled in a semblance and an illusion. This transcendental semblance, or this optical illusion of the reason, exhibits itself differently in each of the different ideas. With the psychological ideas the reason perpetrates a simple paralogism, while with the cosmological it finds itself driven to contradictory affirmations or antinomies, and, with the theological, it wanders about in an empty ideal.

(1.) The psychological ideas, or the paralogisms of the pure reason.

Kant has attempted, under this rubric, to overthrow all rational psychology as this had been previously apprehended. Rational psychology has considered the soul as a thing called by that name with the attribute of immateriality, as a simple substance with the attribute of incorruptibility, as a numerically identical, intellectual substance with the predicate of personality, as an unextended and thinking being with the predicate of immortality. All these principles of rational psychology, says Kant, are surreptitious; they are all derived from the one premise, “I think;” but this premise is neither intuition nor conception, but a simple consciousness, an act of the mind which attends, connects, and bears in itself all representations and conceptions. This thinking is now falsely taken as a real thing; the being of the Ego as object is connected with the Ego as subject, and that which is affirmed analytically of the latter is predicated synthetically of the former. But in order to treat the Ego also as object, and to be able to apply to it categories, it must be given empirically, in an intuition, which is not the case. From all this it follows that the proofs for immortality rest upon false conclusions. I can, indeed, separate my pure thinking ideally from the body; but obviously, it does not follow from this that my thinking can exist really when separate from the body. The result which Kant derives from his critick of rational psychology is this, viz., there is no rational psychology as a doctrine which can furnish us with any addition to our self-knowledge, but only as a discipline, which places impassable limits to the speculative reason in this field, in order that it may neither throw itself into the bosom of a soulless materialism, nor lose itself in the delusion of a groundless spiritualism. In this respect rational psychology would rather remind us, that this refusal of our reason to give a satisfactory answer to the questions which stretch beyond this life, should be regarded as an intimation of the reason for us to leave this fruitless and superfluous speculation, and apply our self-knowledge to some fruitful and practical use.