Page:Philosophical Review Volume 1.djvu/200

184 The German psychologists take a different view of the matter, to judge from the following passages from a recent article by Professor Wundt:

I have often explained why I regard an influxus physicus in the sense of Cartesian dualism as an impossibility, and believe the conception of a parallelism between mental and physical processes to be required by empirical psychology. . . . The Cartesian theory is untenable because it assumes a causal connection between entirely incomparable facts. A sensation can no more be explained by a motion than a motion by a sensation.

It goes without saying that an external movement as a physical process can only be explained by a previous physical process, as for example by a sensory excitation; and that, consistently with the principles of natural causation, there can be no motion for which such an explanation must not be postulated.

Dr. Münsterberg has rightly seen that the possibility or impossibility of interaction between mind and body depends upon the meaning and implications of the relation of cause and effect. While his account of this matter will perhaps prove more suggestive than convincing, it at least seems to me to contain the antidote to a current abuse of the Humian doctrine of causality, to which I wish to devote a few words.

Defenders of interaction tell us that Hume, Kant, and Lotze have shown that we never discern a causal bond uniting the cause with the effect. In the sense that we never perceive an identity between cause and effect, or a transference of energy from one to the other, or anything more than a mere empirical succession, this is doubtless true. But the hasty inference that the relation between cause and effect is impenetrable to reason, in such a way that any cause might conceivably be joined with any effect, is entirely unwarranted. For there exist at least a great number of cases in which cause and effect are connected by qualitative and even quantitative relations which make it appear by no means so irrational that one should be succeeded by the other. One of the most remarkable achievements of modern science consists, for example, in the proof that physical heat is a mode of motion of the minute particles of bodies, and that where ordinary motion is transformed into heat there is an exact equivalence between the amount of motion lost and the amount of heat evolved. In this case, cause and effect are not only qualitatively alike, but an exact quantitative relation exists between them. Now these qualitative and quantitative relations constitute a phenomenal bond