232 PSYCHOTHERAPY: SCIENTIFIC AND RELIGIOUS chap.
because it appears that the physiological events have their own nervous causes and effects and thus form a closed system. This difficulty is avoided, however, in the theory of psychophysical parallelism, which supposes that the mental events are merely parallel processes in the brain, which are themselves links in a series of causes and effects that runs continuously from stimulus to response. Others pose a double-aspect theory, holding that the events in the mind and the brain are not different entities but different aspects of the same underlying entity. Still others support an identity theory on the ground that the underlying entity is not known and that the two aspects are therefore only the same event observed by different methods. It is evident that there is only a shade of difference between these theories when they are considered in this order. Moreover, the difference, being speculative, cannot affect research one way or the other. The first two theories are dualistic ; the last two are monistic ; yet the introspective method is available to either kind of psychologist. The dualist uses it, describing phenomena for their own sake and relating them to neural events as best he may. The monist uses it, regards the results as implying something about the brain, and looks for the same neural relations as best he may. The monist employs the method of sensory discrimination with animals and thinks he has got in his results a measure of neural capacity. The dualist uses the same method and thinks that the same result indicates the differentiation among phenomena in the animal's consciousness. The distinction is not really vital as all these theories remain highly disputable. And as Dr. William Brown28 puts it, ' this probably means that the human mind has not yet succeeded in fashioning concepts adequate for use in so stupendous a task \