THE PRINCIPLE OF LEAST ACTION, KTC. In our treatment of the conception of mental inertia we have reached the following main result. The positive aspect of that continuity of Interest which gives primary unity to Consciousness is essentially an effort at self-realisation, but this positive conation implies a corresponding negative, namely, relative inertia. Relative Inertia is as essential to the unity of mental growth as is continuity of Interest each is in fact implied in and limited by the other. The principle of Least Effort may be taken as the abstract negative expression of the unifying principle of mental development in this sense, that mental progress depends on the elimination of all interests that are alien to the interests that give unity to the mental life, and a renun- ciation of all free effort on behalf of these eliminated interests. IV. THE PRINCIPLE OF FACILITATION (IN THE LIGHT OF CERTAIN LOGICAL DISTINCTIONS). In dealing with Facilitation as a so-called principle of mental process, I propose to deal with two conceptions of lessening effort, the one abstract and negative, the other concrete and positive. In dealing with the former I shall lay special stress on the limitations imposed upon the principle by its abstract character, and I hope to show, in dealing with the latter, that the positive, concretely con- ceived conception of lessening effort may when rightly interpreted, be identified with a most fundamental and fruitful conception in Psychology. If we consider the two essential processes that go on simultaneously in every complete process of mental develop- ment : (1) the elimination of the random, unserviceable and irrelevant in experience, and (2) the elaboration, through mutual adjustment and co-operation of what is relevant ; and if further our way of considering these processes is to fasten on some abstract common element and raise it in virtue of its extreme generality to the rank of a unifying principle of mental process, we fall in my opinion into the most grievous error. For we identify the result of one or more successive processes of abstraction, the so-called abstract universal with the result of a comprehensive synthesis based on a previous thorough-going analysis, the so-called concrete universal. And the principle, whether abstract or concrete, bears its birth-mark stamped upon it. A product formed by mere abstraction is a product possess-
