Interesting and important as are these phenomena, they do but disclose one of the many properties characteristic of living matter. The existence of these properties the man of science accepts on the basis of observation, but he believes that their emergence is related to antecedent conditions of the natural order which are ideally explicable in terms of the sequence of configurations of which evolution is the scientific expression. Naturalism admits that when life first appeared new modes of the interaction of material particles occurred; new data were afforded for science to deal with in accordance with its canons of interpretation; but naturalism does not admit that this necessarily implies an "alien influx into nature." According to the creed of naturalism there is nothing alien introduced into nature from without; all the influences at work are inherent in the fibre of her being; and of these under influences all that we know is that under appropriate conditions certain observable sequences do actually occur. Agnosticism denies that we can draw any inference from the nature of the sequence to a purpose of which it is the expression.
That is one side of the shield. Professor Japp was looking at the other side when he said that when first life arose a directive force came into play a force of precisely the same character as that which enables the intelligent operator, by the exercise of will, to select one crystallised enantiomorph and to reject its asymmetric opposite. Such a directive force is not a scientific conception. Force is not here used as a measure of acceleration; it stands for the raison d'etre of certain facts of observation. And in likening it to the operations of human volition Professor Japp implies that underlying vital phenomena there is a purpose analogous to that with which we are acquainted in the exercise of our own activities. How far naturalism can accept such an analogy we shall consider in the next section. Our present point is that any vitalistic hypothesis is, in so far as it goes beyond an interpretation in terms of antecedence and sequence, non scientific. It is an interpretation in terms of purpose. That such an interpretation is philosophically legitimate is just the position for which I contend. But I would urge that it should not be restricted to the sphere of vital phenomena. It underlies all changes of configuration alike in the sweep of the planets round the sun, the architecture of crystals, the molecular structure of chemical compounds, the electronic system which has recently been disclosed in the atom. It is that which enchants the ether and is manifested to man as the universe. No doubt vital phenomena, from the selection by Penicillium of dextroracemic acid to the wonderful phases of development of the chick from its egg and the whole ranee of racial evolution, seem to emphasise the rationality of purpose, as does also the growth of our knowledge which naturalism is bound to interpret in terms of antecedence and sequence; for after all it is the rational nature of the whole of our experience which for those who can accept the doctrine of purpose testifies throughout to its rational character. As Mr. Balfour says in his British Association address:
Extend the boundaries of knowledge as you may; draw how you will the picture of the universe; reduce its infinite variety to the modes of a single space filling ether; retrace its history to the birth of existing atoms; show how under the pressure of gravitation they became concentrated into nebulae, into suns, and all the host of heaven; how, at least in one small planet, they combined to form organic compounds; how organic compounds became living things; how living things, developing along many different lines, gave birth at last to one superior race; how from this race arose, after many ages, a learned handful, who looked round on the world which thus blindly brought them into being, and judged it, and knew it for what it was perform, I say, all this, and, though you may indeed have attained to science, in nowise will you have attained to a self-sufficing system of beliefs. One thing at least will remain, of which this long-drawn sequence of causes and effects gives no satisfying explanation; and that is knowledge itself. Natural science must ever regard knowledge as the product of irrational conditions, for in the last resort it knows no others. It must always regard knowledge as rational, or else science itself disappears.
The consideration of the growth of our knowledge, however, brings us into touch with mental science. Let us see what naturalism has to say concerning an interpretation of mental phenomena.