What the objectors really mean is that such a relation is incomprehensible, which it certainly is, but so also are all natural phenomena when reduced to their lowest terms.
The argument from equivalence is of greater weight, but is not conclusive. Mental states, it is true, have never yet been measured, nor are they likely to be; but we have no right to assume that quantitative relations are the only relations of which the law of conservation of energy can take cognizance. As quantity is an essential attribute of matter, so is quality an essential attribute of mind, and we may discover that, mutatis mutandis, the law of equivalence holds—that every given quantity and kind of energy expended in the cortex has its fixed equivalent in a given quality of consciousness, that is, in some definite kind of sensation, thought, or emotion, and vice versa.
It should be observed that the argument from the law of conservation of energy overthrows both the theory of independence and that of dependence, and we are reduced to the contemplation of the relation of mind and matter as an inscrutable mystery—a mystery which some philosophers try thinly to veil, by invoking the good offices of a third unknown substance of which both matter and mind are supposed to be attributes. This is the so-called doctrine of monism.
I have thought it necessary to go into this argument to some degree because without some such explanation my readers may wonder why I regard the theory of independence as entitled to any hearing whatever. Yet I think that the disrepute into which it has fallen is not due to any imaginary conflict with the law of conservation of energy. It is in part due to the general drift of our age, which for nearly four hundred years has set away from the supranaturalistic conceptions of the middle ages toward naturalism, and has consequently left the doctrine of independence, which was universal throughout the middle ages, high and dry on the sands. It is for the most part, however, due to the direct evidence, of which I have above spoken, for the dependence of mind upon the body.
It is not my purpose to attempt to prove or to disprove either of these theories, but before proceeding to interpretations of automatism which may be based upon the latter, I may point out that the evidence is not so wholly one-sided as is commonly supposed. The clinical facts by no means warrant the assumption that mental degeneration necessarily keeps pace with brain destruction. Cases are frequently reported in which patients survive severe and permanent injuries to the brain with relatively slight mental impairment. Some of the phenomena of normal psychology, as the consciousness of self, attention, and will, are as easily interpreted from the one as from the other point of view; and in
