The arguments in favor of parallelism may be summed up as follows: (1) The hypothesis is a necessity for scientific psychology. If our psy chological experiments, in which we submit the mind to various forms of physical stimulation, and observe the results, were liable to interrup tion by the reaction of mind itself upon the stimuli employed, there could be no hope of erecting 'laws' of mind, of discovering mental 'uniformities.' Our most laborious and careful researches might be upset at any moment by the interjection of sonic mental influence. The fact that laws and uniformities have been established indicates that the mental is conditioned, un equivocally, by the physical, and that there is no reciprocal conditioning. (2) The categories of mind and body are the most diverse of all that are recognized by science. They are entirely heterogeneous. But it is a rule of logic that one may not argue from category to category; reasoning is valid only within the limits of a single 'kind' or 'genus.' hence we may not in terpolate mental links in the chain of physical causation, and rice rcrsu. (3) Reflex and sec ondary reflex movements show that the organism can act 'teleologically,' i.e. as if with set pur pose and with a view to a determinate end, without the aid of consciousness. (4) The law of the conservation of energy requires that mo tion produce and be produced by motion; it. forbids any arbitrary increase of the energy of the organism, such as must follow from the direct action of mind upon brain-cell.
The first of these arguments is difficult to meet. It rests upon a basis of positive fact; whatever our theoretical belief, we can but grant the utility of the parallelistic principle in the practice of experimental psychology. We might, however, urge that the heuristic value of a work ing hypothesis is no evidence that the hypothesis will endure. A proposition that appears self evident at one stage of the history of a science may be utterly overthrown by later discovery. It may be, then, that as our experimental meth ods grow in refinement, and we attack the higher and more complex processes of mind, we shall gain evidence of the very mental action which now seems to be precluded by the results of ex periment. The second argument is less strong.
No formal considerations can limit the province of cause and effect; experience must decide in each case, irrespective of homogeneity or hetero geneity of the terms. The purposiveness of the reflex movements "proves only that the same effect can proceed from different combinations of conditions" (Stumpf). Moreover, it is prob able that these movements are, one and all, de generate impulsive actions (see ACTION) so that their teleology may, after all, be conscious ly conditioned. Lastly, there is no good reason why we should not rank 'mental energy' along side of chemical. thermal, electrical, etc., energy, and assume that it, like these, has its precise mechanical equivalent.
We shall incline to the one side or the other, then, as our interests and experience prompt. The descriptive psychologist, keenly alive to the manifestations of mental life about him, and influenced by the traditions of psychological thought, will tend toward an acceptance of in teraction; the experimental psychologist, revo lutionary in temperament, and dominated by the methods of the laboratory, will tend toward a parallelistic theory. The impossibility of pres ent decision may mean that we have not as yet sufficient facts at our disposal for a solution of the problem; or it may mean that the pioblem is wrongfully fornmlated, and will be transcend ed by a true philosophy. In either case, we must put our trust in time and further work. And, in the meanwhile, we shall do well to push to its logical extreme the hypothesis which makes the stronger appeal to us, for the clash of honest opinion is of the very greatest import for scien tific progress.
BIBLIOGRAPHY. Jai/ICS, Psychology (New York, Bibliography. Jai/ICS, Psychology (New York, 189(t) ; St umpf, President's Rcricht III. International Congress of Psychology (1897) ; Ebbinghaus, Psycho/ogee (Leipzig, 1897) ; Kuel Out lines of Psychology (London. 1895) ; Titehener, Outlines of Psychology (New York, 1899) ; Wundt, Human and Animal Psychology (Eng. trans., London. 1896) ; Wundt, Outlines of Psychology (Eng. trans., 1898) ; T. 11..
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