Page:Philosophical Review Volume 1.djvu/199

No. 2.] ical with mental. The correct statement is that brain-events are the indispensable condition, or substratum, of mental events.

In what sense is explanation possible in psychology, on the materialistic psychophysical theory? Owing to the characteristics of the mental series mentioned above, — its discontinuity and irregularity, and the frequent appearance of states that are entirely new, — it is obviously impossible to follow the analogy of physical explanation and interpret the mental state of one moment as the adequate cause of the mental state of the next. But a different kind of explanation is possible. "While I write this, tone-sensations invade my consciousness; some one in the next house begins to play upon the piano. Is this intrusion of tone-sensations inexplicable? Psychologically it is, for they were not preceded in consciousness by a content from which I could have inferred their approach. But every mental event is concomitant to an event in the brain, which latter is the necessary result of preceding physical events, and as such perfectly explicable." We may therefore say that a perception or other mental event is explained when it is shown to be the concomitant of a brain-event the occurrence of which at the given moment is intelligible as a result of the physical conditions. The lawful sequences of physical phenomena thus furnish a satisfactory explanation of the otherwise inexplicable sequences of mental phenomena.

In commenting upon the foregoing discussion, I shall speak first of the general theory of parallelism, and later of the special form of it which Dr. Münsterberg professes in his doctrine of the dependence of mind upon body.

The theory of parallelism appears to those who accept it to be a necessary inference from the law of the conservation of energy. If this is, as Helmholtz says, "a universal law of all natural phenomena," it must apply to the motions of molecules in the brain as much as to similar motions outside the body. This is no more than we should expect in view of the mechanical theory of life. But if the conservation of energy applies to brain-events, these must form a locked system, and states of consciousness must accompany without modifying them.

In view of these considerations, it is surely surprising that Professor James in his chapter on mind and body should not even have mentioned the law of the conservation of energy. Professor Ladd at least tells us clearly what he thinks of it, for in his recent Outlines he describes it as "only a valid and useful working hypothesis under which we may bring certain classes of physical phenomena."