[165]. To put the matter more succinctly, as regards the position of Chemistry and Biology, we may say that while chemical and biological facts are never merely mechanical, chemical and biological science, so far as they subserve the strictly scientific interest of calculation and the formulation of general rules, must always be so. The facts only lend themselves to this special purpose in so far as they admit of being, without sensible error, treated as if they conformed to the postulates of universal Mechanism. The special and more difficult case of psychological facts I reserve for separate discussion in the following Book (infra, Bk. IV. chap. 1).
I am glad to be able to refer the reader, for a view of the logical worth of the mechanical postulates which appears in principle identical with my own, to the interesting discussion of Mr. W. R. B. Gibson in Personal Idealism, p. 144 ff.
[166]. Compare Bradley, Appearance and Reality, chap. 23, note 2 to p. 331 (1st ed.); Lotze, Metaphysic, bk. ii. chap. 7, pp. 209, 210 (Eng. trans., vol. ii. p. 89 ff.); Ward, Naturalism and Agnosticism, vol. i. pp. 84-91 (Conservation of Mass), 170-181 (Conservation of Energy).
[167]. If we merely desired to fix the sense of the term mass without introducing the concept of constant mass, we might of course consider two bodies only, A and B. Then the ratio mass of B
———
mass of A = acceleration of A in presence of B
—————————————
acceleration of B in presence of A. See Mach, Science of Mechanics, p. 216 ff.; and Pearson, Grammar of Science, p. 302 (2nd ed.), on which the above account is based.
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.
§ 1. The net result of our brief examination of some of the most important cosmological concepts has been to confirm us in the “idealistic” or “spiritualistic” interpretation of existence to which our first two books in principle committed us. The reader who has followed us so far with acquiescence will now be fully prepared to admit that we shall at least be nearer the truth in conceiving the universe as composed of sentient and purposive subjects of experience, akin in principle to the members of human society, than as constituted, entirely or in part, of mechanically interacting and interdependent elements. The acceptance of an idealist interpretation of the universe, however, still leaves us face to face with a number of problems of the gravest philosophical import. We have still to ask how in particular we can most truly conceive the systematic unity which is formed by the whole multiplicity of apparently more or less independent subjects of experience, what degree of permanence and individuality, so far as we can judge, belongs to ourselves as members of that system, and what light is thrown by our ethical, religious, and æsthetic aspirations and ideals on the concrete character of the whole system and on our own place in it. Again, before we can attack these momentous problems with any reasonable hope of success, we shall need to know which among the categories employed by the various sciences dealing with mental life are of fundamental significance, and what is the logical relation of those sciences to the concrete realities of immediate experience, and to the constructions of physical science. Only on the basis of a rational theory as to the purposes subserved by the various mental sciences, and the possible limitations imposed by those purposes on the use of the corresponding categories, can we decide how far the interpretation of existence as a whole in terms of Psychology, Sociology, or Ethics, is legitimate.
It is clear that the complete execution of the programme indicated in the previous paragraph would involve a systematic philosophical interpretation of the significance of human life for which some such name as the Metaphysics of Society or Metaphysics of History would be a more adequate designation than the traditional title of Rational Psychology. I have, however, retained the ancient name for this subdivision of our task, mainly on the ground that our own elementary discussion will be primarily concerned with those most simple and universal psychological concepts of which the various more concrete social and historical sciences make the same constant use as chemistry and the other physical sciences do of the mechanical concepts of mass, energy, velocity, etc. Whatever view we adopt of the precise degree of connection between Psychology on the one side and the various social and historical sciences on the other, it is at least manifest that Ethics, Sociology, History, and the rest all involve the constant use of such psychological categories as those of self, will, thought, freedom, and that thus any sound metaphysical interpretation of history and society must begin with investigation into the logical character of the science to which these concepts belong, just as a sound Metaphysic of nature had to start by an examination of the postulates of Mechanics. I suppose that there is no need to utter more than a passing word by way of reminder to the reader, that such an investigation presupposes the previous creation of a purely empirical science of Psychology. The business of Metaphysics with Psychology is not to dictate in advance how it must construct its view of the world, but to ascertain the logical character of the completed construction, and its relation to the general system of human knowledge.