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] be deceived into supposing that these factors, or "moments" of psychic life, are entities, after the fashion of the atom, or molecule, dealt with by the natural sciences of chemistry and molecular physics. But they are entities in the sense in which psychic facts are entities. The existence of some of them can be readily detected by such analysis as self-consciousness can make; while others of them are rather speculative necessities postulated in the effort to account for the varying characteristics of those complex phenomena which constitute the primary problems of psychology.

But besides this explanation by analysis, the science of psychology has the task of tracing the evolution of mental life. The conception of evolution is as much needed, and as light-bringing, in the treatment of mental as of any other form of life. Here the natural sciences — in the strict sense of the word "natural" — may be evoked to tell of the physical conditions, under which the genesis and development of mental life takes place. But we make a very meagre, an unnecessarily meagre, use of the principle of development, if we fail to apply it directly to mental life itself. The life of consciousness falls directly under this principle. Its various stages are related to each other, under law, according to the conception which this principle emphasizes. When we point out 'uniform relations, the dependence of mental state on mental state, of one stage of mental life on other stages of mental life, we render psychology scientific. For the psychologist to surrender all right to claim that he "explains" psychic facts by tracing their causes in other antecedent and concomitant psychic facts — as Mr. Hodgson and Professor James appear ready to do — is to "sell his birthright for a mess of pottage." For a "mess of pottage," or little better, is the present content of cerebral physiology as explanatory even to the extent of establishing "blank unmediated correspondences" — of the fundamental, as well as of the so-called higher, activities of mind.

But may we pursue psychology as a "natural science" without postulate of a soul, and without any metaphysical implicate or postulate whatsoever? Possibly: I am not prepared to say