The world of objects which is thus consti tuted through the forms of perception and the categories is only phenomenal; that is, only the world as it appears to us, not the world of but we are obliged to think things-in-them selves always remain for Kant a real back ground with which he contrasts the world of phenomena. We can know only phenomena, but we are obliged to think selves as existing, though we cannot give •them any positive determination. Kant seems to re Bard them as the causes of the sensations which arise in the mind. But, since casuality is a category supplied by the mind, it can only apply to objects as known, and hence cannot consistently be taken to apply to things-in themselves. It is very difficult to make Kant consistent on this point. It is certain that he continues to contrast the world as known with a more ultimate form of reality which remains beyond the sphere of knowledge but whose cer tainty is guaranteed by faith or practical rea son; and it is equally certain that the spirit of his philosophy tends to break down the very opposition which he has set up so carefully.
The Understanding (der Verstand), as Kant says, is the faculty of rules. It is its function to reflect on the objects presented to it by sense-perception in order to find the rule or category according to which one part can be united to another. But its objects must always be given to it in sense-perception, and it can do nothing but unite one object as given in space and time with another according to some gen eral rule. From the very nature of the case, then, it can never complete its task and rise to deal with and determine the nature of a real totality. Its concern is always with phenomena, with objects in space and time and their syn thesis; and, as these extend indefinitely, the understanding, therefore, never can find rest in the establishment of a completed totality. Now for Kant the limits of the Understanding are the limits of valid knowledge. We cannot know anything but phenomena and the laws of their connection. But there is another theo retical faculty which he opposes to Under standing under the name of Reason (die Ver nunft). This is the great source of illusion. Reason transcends lthe sphere of the Under-' standing and attempts to find for objects an unconditioned basis in the ideal or Idea of an ; ., absolute and no -phenomenal unity. In this it has a certain justification as affording an ideal of unity to and which the Understand ing must always strive in its investigations; but it leads to lillusion when this idea of a unity is taken as• a real object of lcnowledge and positive determinations are ascribed to it.
Kant proceeds t6 apply this criticism in detail to the so-called sciences of the Rationalism (q.v.) of his fay,— psychology, cosmology and theology,—pointing out that all these are illu sory, since they are based on concepts of ob jects (the soul, the world, God) that lie beyond the sphere of possible experience. The conclu sions drawn by rational psychology regarding the simplicity and immortality of the soul Kant rejects as °paralogisms.° For, as he shows, we have no valid concept of the soul as a thing or substance, upon which to base our conclu sions. °transcendental ego' is not some thing which can be determined as a soul-sub stance ar /an object of a particular kind. It is always sUbject and never object,— the universal presupposition of experience, not an experi enced!fhing; for an object can only be known when ka sensation corresponding to it is given or may be given in experience. All the wisdom of rational psychology, which is based, on the pure concept of the soul, Kant therefore re jects. In the same way he shows that over against the various theses demonstrated by rational cosmology regarding the nature of the world as a whole (that it is limited in time and space; is composed of simple parts; that in addition to natural causality it admits of free causality; that it has a necessary grousid), the antithesis or direct contradictory of each prop osition can be demonstrated with equal co gency. The inevitable contradictions which thus result in the field of cosmology when we attempt to go beyond possible experience and make assertions regarding the world as a whole, Kant names the °Antinomies of Pure Reason Those regarding the extension and divisibility of the world disappear as soon as we remem ber that space and time do not belong to things in-themselves, but are only forms of perceptive experience. With regard to the possibility of freedom Kant points out that although the principle of natural causation must hold with out exception of phenomena, the question still remains open whether freedom may not find plate in the intelligible world of things-in themselves. This question cannot be answered on theoretical grounds but remains a mere possibility which can only be settled by appeal ing to practical considerations. Kant's criti cism of theology is still more famous. He finds that all the proofs for the existence of God may be classified as the Ontological, the Cosmological and the Teleological. He shows that none of these proofs is valid from a log ical point of view, and that the existence of God is therefore incapable of theoretical dem onstration.