inspired by æsthetic and historical as well as by primarily “scientific” interests. § 6. The analysis of such leading concepts of mechanical Physics as the Conservation of Mass and of Energy shows them to have only _relative_ validity 279 BOOK IV RATIONAL PSYCHOLOGY—THE INTERPRETATION OF LIFE CHAPTER I THE LOGICAL CHARACTER OF PSYCHOLOGICAL SCIENCE § 1. The various sciences which deal with the interpretation of human life all avail themselves of the fundamental categories of Psychology. Hence we must ask how the concepts of Psychology are related to actual experience. § 2. Psychology is a body of abstract descriptive formulæ, not a direct transcript of the individual processes of real life. It presupposes the previous construction of the physical order. § 3. The psychological conception of conscious life as a succession of “mental states” or “images” is a transformation of actual experience devised primarily to account for the experience of other subjects, and subsequently extended to my own. The transformation is effected by the hypothesis of “introjection.” §§ 4, 5. The logical justification of the psychological transformation of facts is twofold. The psychological scheme serves partly to fill up the gaps in our theories of physiological Mechanism, and also, in respect of the teleological categories of Psychology, to describe the course of human conduct in a form capable of ethical and historical appreciation. Psychology may legitimately employ both mechanical and teleological categories. § 6. The objections sometimes brought against the possibility of (_a_) psychological, (_b_) teleological description are untenable 294 CHAPTER II THE PROBLEM OF SOUL AND BODY