BODY AND MIND. The question of the rela tion of body to mind, together with the deeper question whether we have a right to separate these two terms and to speak at all of a 'relation' between them, is subject-matter for metaphysical inquiry. We refer to the articles DUALISM; EPISTEMOLOGY; MATERIALISM; .MONISM: SPIRIT UALISM. here we are concerned simply to dis cuss the views which have been adopted by psychologists as working hypotheses upon the scientific level, without regard to their ultimate metaphysical validity. Just as physics may pos tulate, for its own purposes, the existence of a. matter which certain philosophical systems repu diate, so may psychology accept a theory of the relation of mind to body which some or all sys tems of philosophy would pronounce erroneous or inadequate. Every science must assume its data as realities, and has a right to its working hypo theses. And some sort of theory of the relation of mind to body has become a necessity for psy chology, since Fechner (q.v.) has shown that the presupposition of an exact science of mind. is the uniformity of mental response to physical stimulus.
Psychologists are, at the present day, sharply divided into two groups, the one holding a theory of the interaction of mind and body, the other a theory of psycho-physieal parallelism. The former theory, which has all the weight of com mon opinion on its side, avers that mental proc esses are able to act causally upon bodily; that an idea may 'make' us act—i.e. condition bodily movements—just as truly as a blow may make us feel pain. The chain of events is made up of two kinds of links—material processes and men tal processes; and the links are interchangeable and equally effective. The latter theory main tains that the two series, the material and the mental, are disparate; that they never pass into or interfere with each other. The mental series i.econditioned upon the material, runs parallel with it. term for term; but there neither is nor can be any transition from the one to the other. It should be said, emphatically, that there is no necessary connection between the theory of interaction and a metaphysical monism or idealism. and none between parallelism and a metaphysical dualism or materialism. Either theory, held as a scientific working hypothesis, is compatible with any one of these ultimate metaphysical beliefs.
The main arguments for interaction are as follows: (1) "'Ile particulars of the distribu tion of consciousness point to its being effica cious" (James). Consciousness can apparently
'load the dice' of the brain — i.e. can bring "pressure to bear in favor of those of its per formances which make for the most permanent interests of the brain's owner." "Consciousness is only intense when nerve-processes are hesitant.
Where indecision is great consciousness is agonizingly intense." This argument squares with the doctrine of biological evolution, in that it gives to mind, which is a highly complex de velopment, a survival value in the organism's struggle for existence. (2) A damaged brain may recover and work normally; the parts re maining take on the duties of the parts lost, by the principle of 'vicarious function.' The res toration is intelligible if consciousness direct it; unintelligible, if the brain machine be subject to no such direction. (3) Pleasures are associated with beneficial stimulation, pains with detri ment to the organism. This correlation seems to imply that pleasures and pains exert a direct influence upon the bodily processes. (4) The assumption of the interaction of mind and body assures the universality of the causal connection and the uniformity of natural law throughout the known universe.
To the first argument there is the reply that it offers no proof of the actual interference of consciousness in the struggle for existence. INlind may be a mere concomitant of brain; a con comitant that varies in complexity as its physi cal substrate varies, and that is thus an index or symptom of brain-eflicacy; but that is not itself a factor in survival. An animal may sur pass its fellows, not because it has a better mind, but because (as its better mind shows) it has a better brain. The presence of an intense con sciousness during deliberation and doubt offers no difficulty. (See ACTION; ANIMAL PsYcnOL oGY.) As for vicarious function, the developed brain is, by hypothesis, an exceedingly complex and plastic structure. not a machine definitely shaped for a few particular ends. Hence there is no need for the intervention of consciousness. The correlation of pleasure with stimuli that further life, and of pain with stimuli that thwart it, is readily explicable as a coincidence due to the continued operation of natural selection (Spencer). An animal that 'liked' to be hurt would not exercise any considerable influence upon the further development of its species. Finally, the demand for a universal causality is rather a metaphysical than a scientific postu late.