psychology, sociology, ethics are, broadly considered, concerned only with incidents of the later scenes of the great mechanical drama of evolution. Are we not again and again bidden, now in forecast, now in retrospect, to look below the surface, and constantly to bear in mind that the aim of philosophy, as completely unified knowledge, is 'the interpretation of all phenomena in terms of Matter, Motion, and Force'?[12] It is true that the affairs of the mind give pause and seem to present something of a difficulty. But even here 'specifically stated, the problem is to interpret mental evolution in terms of the redistribution of matter and motion'.[13] An adequate explanation of nervous evolution involves an adequate explanation of the concomitant evolution of mind. It is true that the antithesis of subject and object is never to be transcended 'while consciousness lasts'.[14] But if all existence, distinguishable as subjective, is resolvable into units of consciousness, which in their obverse or objective aspect are oscillations of molecules,[15] what more is required to round off the explanation of every thing, save the Unknowable—save the Ultimate Reality in which subject and object are united? In the end we are baffled by mystery; let us, therefore, make the best of it and rejoice.

'We can think of Matter only in terms of Mind. We can think of Mind only in terms of Matter. When we have pushed our explorations of the first to its uttermost limit we are referred to the second for a final answer; and when we have got the final answer to the second we are referred back to the first for an interpretation of it.'[14]

And so neither answer is final. Finality is only reached when both are swallowed up, not in victory, but in defeat. Shall we not then glory in defeat and sing its praises often?

I must leave to some future Herbert Spencer lecturer the discussion of his doctrine of the Unknowable and the critical consideration of its place and value in philosophy. I would fain leave it altogether on one side; but that is impossible. Although the First Principles is divided into two Parts, dealing respectively with the Unknowable and the Knowable, we have not by any means done with the former when we turn from the First Part to the Second. With Spencer we have never done with the Unknowable, the Unconditioned Reality and the other aliases by which it goes. His persistence of force is the persistence of Unknowable Force. In a leading passage, at any rate, it is avowedly 'the persistence of some Cause which transcends our knowledge and conception. In asserting it we assert an Unconditioned Reality without beginning or end'.[16] There must, he holds, be something at the back of the evolutionary drama which we study—something that is both a principle of activity and a permanent nexus.[17] The pity of it is that we know not, and can never know, what on earth (or in heaven!) it is. We only know that it exists, and somehow produces the whole show. Now it would much conduce to clearness of thought and of statement if we could agree to eliminate those terribly ambiguous words 'force' and 'cause' when we are dealing with the fundamental postulate (if such it be) that there must be something at the back of evolution to make it what it is; and the word Source seems ready to our hand and might well be given this special significance. But Spencer uses Agency, Power, Cause, Force, in this connexion. In how many senses he uses the word 'force' I am not prepared to say. It is often a synonym for cause; it stands alike for matter and energy;[18] it is the objective correlate of our subjective sense of effort.[19] There is a 'correlation and equivalence between external forces and the mental forces generated by them under the form of sensations'.[20] And when we pass to human life in society, whatever in any way facilitates or impedes social, political, or economic change, is spoken of in terms of force.[21] With an apparent vagueness and laxity almost unparalleled, force is used in wellnigh every conceivable sense of this ambiguous word—except, perhaps, that which is now sanctioned by definition in mathematical physics. I say apparent vagueness and laxity because, subtly underlying all this varied usage, is the unifying conception of Source as the ultimate basis of all enforcement. From this flows all necessity whether in things or thoughts or any combination of the two. Thus persistence of force is Spencer's favourite expression for uniform determinism at or near its Source.

Now, as I understand the position, science has nothing whatever to do with the Source or Sources of phenomena. By a wise self-denying ordinance it rules all questions of ultimate origin out of court. It regards them as beyond its special sphere of jurisdiction. It deals with phenomena in terms of connexion within an orderly scheme, and it does not profess to explain why the connexions are such as they are found to be. In any discussion of this or that sequence of events which may fall under the wide and rather vague heading of evolution, it is just a consistent story of the events in their total relatedness that science endeavours to tell. The question: But what evolves the evolved? is for science (or should I say for those who accept this delimitation of the province of science?) not so much unanswerable in any terms, as unanswerable in scientific terms. For the terms in which an answer must be given are incommensurable with the concepts with which science has elected to carry on its business as interpreter of nature. To this question therefore the man of science, speaking for his order, simply replies: We do not know. Is this, then, Spencer's answer? Far from it. The man of science here makes, or should make, no positive assertion, save in respect of the limits of his field of inquiry. If you beg him to tell you what that which he knows not is, or does, he regards such a question as meaningless. But Spencer's Unknowable, notwithstanding its negative prefix, is the Ultimate Reality, and does all