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 that is in any way done. We may not know _what_ it is; but _that_ it is, is the most assured of all assured certainties. And when it comes to doing, what can be more dramatically positive than that which bears a name of negation? Whatever it may not be, it is the Power that drives all the machinery in this workshop of a world; it is the Power which lies at the back of such wit as man has to interpret it, and, in some measure, to utilize its mechanism.