It remains to add that this great difficulty against the spiritualistic theory has been revealed in all its force only during the present generation. Since the days of fetishism, indeed, the difficulty has always been an increasing one—growing with the growth of the perception of uniformity on the one hand, and of mechanical as distinguished from volitional agency on the other. But it was not until the correlation of all the physical forces had been proved by actual experiment, and the scientific doctrine of the conservation of energy became as a consequence firmly established, that the difficulty in question assumed the importance of a logical barrier to the theory of mental changes acting as efficient causes of material changes.
CHAPTER II.
MATERIALISM.
This is the theory which presents great fascination to the student of physical science. By laborious investigation physiology has established the fact beyond the reach of rational dispute, that there is a constant relation of concomitancy between cerebral action and thought. Within experience mind is found in constant and definite association with that highly complex and peculiar disposition of matter called a living brain. The size and elaboration of this peculiar structure throughout the animal kingdom stand in conspicuous proportion to the degree of intelligence displayed; while the impairment of this structure, whether by congenital defect, mutilation, anaemia, decay, or appropriate poison, entails corresponding impairment of mental processes. Thus much being established, no reasonable man can hesitate in believing the relation between neurosis and psychosis to be a constant and concomitant relation, so that the step between this, and regarding it as a causal relation, seems indeed a small one. For, in all matters of physical inquiry, whenever we have proved a constant relation of concomitancy in a sequence A B, we call A the cause of B; and, therefore, it has been frequently said that the evidence of causation between neurosis and psychosis is recognized causation. Lastly, to fortify this hypothesis, materialists point to the doctrine of the conservation of energy, which is supplied by the science of physics as a sort of buttress in this matter to the teachings of physiology. For, as this doctrine compels us to believe that the chain of physical causation involved in cerebral processes can nowhere be broken or deflected ab extra, we are compelled to believe that the mental processes, which are correlatively associated with these cerebral processes, can nowhere escape from 'the charmed circle of the forces,' so that whether we look to the detailed teachings of physiology, or to the more general teachings of physics, we alike perceive that natural science appears to leave no locus for mind other than as a something which is in some way a result of motion.
The position of Materialism being thus at first sight so naturally strong, and having been in recent years so fortified by the labours of physiology, it is not surprising that in the present generation Materialism should be in the ascendant. It is the simple truth, as a learned and temperate author, speaking from the side of theology, has recently said, that
'Materialism is a danger to which individuals and societies will always be more or less exposed. The present generation, however, and especially the generation which is growing up, will obviously be very especially exposed to it; as much so, perhaps, as any generation in the history of the world. Within the last thirty years the great wave of spiritualistic or idealistic thought ... has been receding and decreasing; and another, which is in the main driven by materialistic forces, has been gradually rising behind, vast and threatening. It is but its crest that we at present see; it is but a certain vague shaking produced by it that we at present feel; but we shall probably soon enough fail not both to see and feel it fully and distinctly[4].'
Such being the present importance of Materialism, I shall devote the present chapter to a consideration of this theory. Each of the points in the argument for Materialism which I have mentioned above admits, of course, of elaboration; but I think that their enumeration contains all that is essential to the theory in question. It now devolves upon us to inquire whether this theory is adequate to meet the facts.
And here I may as well at once give it as my own opinion that, of however much service the theory of Materialism may be, up to a certain point, it can never be accepted by any competent mind as a final explanation of the facts with which it has to deal. Unquestionable as its use may be as a fundamental hypothesis in physiology and medicine, it is wholly inadequate as a hypothesis in philosophy. That is to say, so long as there is a constant relation of concomitancy found by experience to obtain between neural processes and mental processes, so long no harm can accrue to physical science by assuming, for its own purposes, that this relation is a causal one. But as soon as the question concerning the validity of this assumption is raised into the region of philosophy, it receives the answer that the assumption cannot be allowed to pass. For where the question becomes one not as to the fact of the association but as to its nature, philosophy, which must have regard to the facts of mind no less than to those of matter, must pronounce that the hypothesis is untenable; for the hypothesis of this association being one of causality acting from neurosis to psychosis, cannot be accepted without doing violence, not merely to our faculty of reason, but to our very idea of causation itself.
A very small amount of thinking is enough to show that what I call my knowledge of the external world, is merely a knowledge of my own mental modifications. A step further and I find that my idea of causation as a principle in the external world is derived from my knowledge of this principle in the internal world. For I find that my idea of force and energy in the external world is a mere projection of the idea which I have of effort within the region of my own consciousness; and therefore my only idea of causation is that which is originally derived from the experience which I have of this principle as obtaining among my own mental modifications.