236 CEITICAL NOTICES : bility of mathematical functions, for in the former case we have to do with determinateness of events, of things that happen. But a conditioned relation of events forms the chief, if not the sole, content of the causal connexion, and it is difficult to see how, on any merely logical grounds, a causal conception, in the sense in- dicated, between the two terms can be denied to be possible. Cartesian dualism is, of course, not here in question, and the applicability of the ambiguous and, on a certain interpretation palpably false, scholastic dictum, catisa cequat effectum, is, to say the least, extremely doubtful. There remain, however, the metho- dological considerations derived from the principle of the conser- vation of energy. Prof. Jodl, indeed, regards this principle, in connexion with the law of inertia, as the most consistent and precise expression of the law of causality in natural science (p. 63), and it is on this ground that he denies that there is any causal connexion between the soul and the body (p. 76). But so understanding the causal conception, he must either give up his view of a causal connexion between the terms of the psychical process (p. 74), or else deny that psychology is a natural science. He frankly admits, as all must do, the gaps in our knowledge of the transformation of energy, especially in the nervous system, and allows that if any one chooses to fill these out by assuming- that at certain points psychic forces affect the motions of the ner- vous substance, he cannot be absolutely refuted by facts ; but, he says, one who does this should take heed lest, in place of an im- perfection in our knowledge, he substitute a contradiction in our fundamental assumptions. " For if psychic force is to act on a. system of material forces, the only way it can do this is by accel- erating or retarding motion ; but how this is possible is more difficult to conceive than it is to fill out hypothetically the gaps- in the physical continuity of the neural process (p. 63). This is not the place, nor is the present writer competent, to criticise in any detail the principle of the conservation of energy. It is evi- dent, however, as Mr. Bradley has pointed out, that a distinction must be drawn between the principle as a postulate of physics science, in which sphere its utility is undisputed, and as a state ment of fact concerning the whole physical universe, as which it as certainly cannot be proved. Moreover, it is obvious to any one who has followed, however superficially, the course of recent dig cussion, that the modern doctrine of energy, and with it the whole of the modern doctrine of matter, is still in process of being de veloped. If chemical theory should move along the lines sug- gested by Ostwald and if, under the influence of speculative physics, the molecular theory of matter, which has so long helc sway, should be superseded by a theory of interchanging energies it would be but a step to the conception of psychical energy anc psychical work as correlated, under the law of conservation itsel though more universally conceived than at present, with the othe natural forms of energy ; and this would lead perhaps to
