But though the advances made by the sciences since Kant’s time have rendered this mode of delimiting the field of knowledge altogether untenable, his method of defining the sources of _philosophical insight_ has proved very fruitful, and has many adherents at the present day. What Kant does--stated in broad outline--is to distinguish between the problems of _existence_ and the problems of _value_, assigning the former to science and the latter to philosophy.[52] Theoretical philosophy, represented in his system by the _Critique of Pure Reason_, takes as its province the logical values, that is, the distinction of truth and falsity, and defining their criteria determines the nature and limits of our theoretical insight. Kant finds that these criteria enable us to distinguish between truth and falsity only on the empirical plane. Beyond making possible a distinction between appearance and reality, they have no applicability in the metaphysical sphere. The _Critique of Practical Reason_ deals with values of a very different character. The faculty of Reason, which, as already noted,[53] renders our consciousness a purposive agency controlled by Ideal standards, is also, Kant maintains, the source of the moral sanctions. But whereas in the theoretical field it subdues our minds to the discipline of experience, and restrains our intellectual ambitions within the limits of the empirical order, it here summons us to sacrifice every natural impulse and every secular advantage to the furtherance of an end that has absolute value. In imposing duties, it raises our life from the “pragmatic”[54] level of a calculating expediency to the higher plane of a categorical imperative. The categorical imperative at once humbles and exalts; it discloses our limitations, but does so through the greatness of the vocation to which it calls us. “This principle of morality, just on account of the universality of the legislation which makes it the formal supreme determining principle of our will, without regard to any subjective differences, is declared by the Reason to be a law for all rational beings.... It is, therefore, not limited to men only, but applies to all finite beings that possess Reason and Will; nay, it even includes the Infinite Being as the Supreme Intelligence.”[55] Consequently, in employing moral ends in the interpretation of the Universe, we are not picturing the Divine under human limitations, but are discounting these limitations in the light of the one form of value that is known to us as absolute. “_Duty!_ ... What origin is worthy of thee and where is to be found the root of thy noble descent ... a root to be derived from which is the indispensable condition of the only worth that men can give themselves.”[56]