If it is said that, objectively considered, psychical events are brain-movements, the simple answer is, that a thought which is a physical movement is as great an absurdity as a piece of iron which is made of wood. Thought is not motion, but thought. The only plausible way of reducing psychical to physical events is to say that the former are the effect of the latter. On this view we must suppose that a brain-movement is transformed into a sensation of definite quality and intensity which is its equivalent. Now, sensation is not motion, and hence we must suppose that, as energy is known only through its expression in motion, a certain quantity of energy has been destroyed. We are therefore shut up to the alternative of denying the principle of the conservation of energy, or abandoning the supposed causal relation of psychical and physical events. In point of fact, even materialists like Büchner virtually adopt the latter view when they say that "thought and extension are two aspects of the same being." Now, this doctrine of the parallelism of psychical and physical events, to be a satisfactory explanation of reality, must be extended to every form of being. Hence, in the first place, the Cartesian idea of automatism must include, not only plants and animals, but also man. But, in the second place, we must equally extend the psychical principle to all things, to plants and minerals as well as to animals and man. It is true that we have no direct knowledge of the inner life of any being but ourselves. Psychical phenomena are given to us only at one point, in self-consciousness, whereas all other beings are presented to us only on their physical side, as moving bodies. But just as we infer the inner life of human beings from the physical movements which is their outer expression, so we are entitled to reason to the inner life of even inorganic things in the same way. Thus we get rid of the difficulty which besets the materialistic view of the causal relation of inner and outer events. The causal relation obtains only between physical events, or between psychical events, never between physical and psychical. If we follow the chain of movements from the vibration of a bell to the final movement in the brain we find that there is between them a causal relation; but the sensation of sound is not the effect of these external movements, but of the psychical events which correspond to them point for point. Our author, in short, is an uncompromising advocate of the 'mind-stuff' theory, which he regards as established by the impossibility of drawing any hard and fast line between the various orders of existence, by the identity of the elementary constituents of inorganic and organic bodies, by the impossibility of
