free use of the conception of consciousness as a co-ordination of forces capable of occasional disruption, although he seems to have been led to that notion by the Herbartian psychology. Professors Janet and Binet also teach analogous doctrines without reference to the brain processes, and Prof. William James seems at times to hold a similar position.
In sharp antithesis to the theory of dependence stands the theory of independence. According to this doctrine, mind and matter are essentially distinct in nature, and are capable of independent existence, although in fact sometimes closely related. Many mental states, as sensations, are caused by physical processes, and, vice versa, many physical processes, as some bodily movements, are caused by mental states; but this relation of action and interaction is purely accidental, and can be dissolved without the destruction of either mind or matter. This theory has been stated in many forms, and is involved more or less implicitly in many philosophies. In one form or another it has been the dominant theory in every epoch of human thought, it lies at the foundation of most religions, and is to-day accepted by the mass of men; yet in the scientific world it has fallen into such disfavor that in many circles it is almost as disgraceful to avow belief in it as in witchcraft or ghosts.
The chief argument usually alleged in justification of this attitude is that the theory of independence violates the law of conservation of energy, which is justly regarded as one of the greatest scientific generalizations of this century. That law requires that in all the manifold flux of physical phenomena certain definite and quantitative relations should exist between the amount of work done and the amount of energy expended, thus binding all physical processes into a closed series. To admit mental phenomena into that series as a mode into which physical energy might be transformed would, it is claimed, break the law—first, because the new elements are non-physical, and it is inconceivable that the non-physical should affect the physical; and, second, because mental states can not be measured, and therefore can not constitute an equivalent of anything.
This a priori objection does not seem to me to possess much force. The argument from inconceivability has been urged against every new conception introduced into science; it was never more weighty then when hurled against the bold speculators who claimed that the earth was round and that the antipodes nevertheless did not fall off. That a thought should cause the disintegration of a molecule is intrinsically neither more nor less inconceivable than that a disturbance in an imponderable entity like ether should shatter an oak tree. What is inconceivable to one generation becomes the commonplace of the next.
