The independence and underivability of the psychical, the incomparability of its uniformities with those of mechanical or physico-chemical laws, has proved itself so clear and incontrovertible, notwithstanding all the distortions of naturalism, that it is now regarded as a self-evident fact, not only among philosophers and epistemologists, and technical psychologists, but for the last decade even among all thinking men, and “materialism” is now an obsolete position. It was too crude and too contrary to all experience to define the relation between physical and mental, as if the latter were a mere secretion of the former, although a very subtle one, or a mere epi-phenomenon of it, in such a way that all reality and effectiveness was on the side of the physical.
In place of this, another theory has become widespread, which claims to define the relation of the two series of phenomena better and more adequately: the theory of psychophysical parallelism. It is not new. There are occasional indications of it even in Aristotle’s psychology. It was suggested by Descartes in his automaton theory, by the occasionalists in their parable of the two watches running in exact agreement; it was developed by Spinoza and Leibnitz, and refined by the idealistic philosophers, by Schopenhauer, Fechner, and the modern psychologists. The form in which it is most prevalent now is that given to it by Spinoza, and he is usually referred to in connection with it. Its general tenor is as follows: The physical cannot be referred back to the psychical, nor the psychical to the physical. Both orders of phenomena run side by side as parallels that never separate. Both represent a concatenation of causes complete in itself, that is never broken, or interrupted, or completed. And in both there is real causality. Thought really causes thoughts and feelings. Movement really causes movements. But the one series is always strictly correlated with the other, and corresponds with it. And thus all existence is double, and man is an obvious illustration of this. To every thought, feeling, or exercise of will there corresponds some excitement, movement or change in the body. I will: my arm moves. Subtle nervous processes run their course in my brain, and I think. That I will has its sufficient reasons, its causes lie entirely in the preceding state of my mind, in motives of feeling, in ideas which again have their efficient causes in a previous psychical condition, and so on. And that my arm moves has its efficient cause in the stored-up energies of the muscle-substance, in the stimulus and impulse conveyed by the motor nerve from the brain. And these conditions have their purely physiological causes and reasons again in preceding purely physiological states and processes. (It goes without saying that a mechanical theory of life is the necessary presupposition of this parallelistic theory.) But both sets of processes correspond exactly one to another, and the first is only the inner aspect of the second, and the second the outer aspect of the first. Thus it is quite true that my arm moves when I will. But in reality it is quite as true to say that when my arm moves I will. But we must not substitute “because” for “when.” This theory must maintain, and does maintain, that even the most abstract and subtle ideas, the deepest processes of consciousness, have some corresponding bodily processes, either in the brain or in the nervous substance generally, and, on the other hand, that no physical process is without this psychical inwardness. The result is that this inwardness and soul are attributed also to the purely material world, the world of “dead” matter. In this way it is believed that everything gets its due; the thorough mechanical explicability of bodily phenomena, and the law of the conservation of energy and of matter, and, on the other hand, very decisively also, the independence and uniqueness of law which can no longer be denied to the psychical. And from this latter standpoint sharp protests are raised against all materialistic distortions. The only thing denied is the old idea of the “influxus physicus,” the idea, that is, that mind can operate beyond itself and take effect on the physical world, and conversely the physical world upon it. This again is regarded as a breach of the law of the conservation of energy. For if the bodily affects consciousness, then at a given moment a certain amount of energy must be transformed into something that is not energy. And if consciousness affects the bodily, a process of movement must suddenly occur, for which no previous equivalent of energy can be shown.