the popular mode of apprehension is distinguished from the scientific in being a compound of experience and metaphysics, and we have here such an instance. But his own clear and guarded statement is as follows:
That we feel this immediately seems to be contradicted by the want of agreement as to the existence of a mind distinct from the body, and by the fact that it is only indirectly that we have come to know with which part of the body the mind is more particularly connected. We can not maintain that the bodily process causes the mental process, because the bodily process (the state of brain connected with sensation) does not itself become an object of consciousness. And if physiology could give a scientific explanation of the condition of the brain that ensues when I am struck by a stone, the feeling of pain aroused in me would not be included in the physiological explanation. Physiology explains a material process by means of other material processes. Its assumptions can not include a case in which one member of the causal relation shall be spatial and the other nonspatial.
Nor does the doctrine of the persistence of energy support the idea of a causal relation between the mental and material. "The doctrine of the persistence of energy is a purely physical doctrine. Such an extension would imply the possibility of finding a common measure for the mental and material. Now, what denominator is common to a thought and a material movement, or what common form serves for both? Until such a common form can be pointed out, all talk about an interaction between the mental and material is, from a scientific point of view, unjustified. So long as we confine ourselves to the material we are on safe ground, and so long as we confine ourselves to the mental we are on safe ground; but any attempt to represent a transition from physical to psychological laws, or conversely, brings us face to face with the inconceivable. The causal concept can not be employed to connect two factors which have no common measure. Again:
"If the relation between mind and body, or consciousness and brain, is a causal relation, there must be a difference of time between the process in the brain and the act of consciousness. This, however, is contrary to the view suggested by physiology. The aim of modern physiology is to conceive all organic processes as physical or chemical. Where it has attained to a comprehension of anything in the region of organic life, this has in every case been by the tracing back of organic phenomena to physical and chemical laws. If, then, there is a transition from physiological function to psychological activity, from body to mind, physiology, at any rate, working with its present method, can not discover it.... So far as we can speak of final results in the physiology of the brain, it is represented as a republic of nerve-centers, each with its function and all in interaction; but there is nothing to indicate the possibility of the physiological process breaking off at any point to pass into a process of a wholly different kind." But in framing our hypotheses we may not enter into conflict with leading scientific principles. "And, in modern natural science, the doctrine of energy is such a leading principle. If, therefore, an hypothesis is in conflict with such a doctrine, the fact tells at once decidedly against it."
