In the second place, since susceptibility to a pleasure or pain can be known only empirically and cannot hold in the same degree for all rational beings, a principle which is based on this subjective condition may serve indeed as a maxim for the subject which possesses this susceptibility, but not as a law even to him (because it is wanting in objective necessity, which must be recognized a priori); it follows, therefore, that such a principle can never furnish a practical law. {BOOK_1|CHAPTER_1 ^paragraph 20} III. THEOREM II. All material practical principles as such are of one and the same kind and come under the general principle of self-love or private happiness. Pleasure arising from the idea of the idea of the existence of a thing, in so far as it is to determine the desire of this thing, is founded on the susceptibility of the subject, since it depends on the presence of an object; hence it belongs to sense (feeling), and not to understanding, which expresses a relation of the idea to an object according to concepts, not to the subject according to feelings. It is, then, practical only in so far as the faculty of desire is determined by the sensation of agreeableness which the subject expects from the actual existence of the object. Now, a rational being's consciousness of the pleasantness of life uninterruptedly accompanying his whole existence is happiness; and the principle which makes this the supreme ground of determination of the will is the principle of self-love. All material principles, then, which place the determining ground of the will in the pleasure or pain to be received from the existence of any object are all of the same kind, inasmuch as they all belong to the principle of self-love or private happiness. {BOOK_1|CHAPTER_1 ^paragraph 25} COROLLARY. All material practical rules place the determining principle of the will in the lower desires; and if there were no purely formal laws of the will adequate to determine it, then we could not admit any higher desire at all. REMARK I. {BOOK_1|CHAPTER_1 ^paragraph 30}