Relation of Theoretical to Practical Philosophy'. It deals—unfortunately far too briefly—with the postulate of Theism, or at least of Moral Order, as a solution of the divergence between 'what is' and 'what ought to be'.
It may be admitted that philosophers sometimes spend too much time in the demarcation of the different departments of their subject. To assign a problem to a specific department is not to solve it, and a reader impatient of formal distinctions and anxious for real nutriment may occasionally suspect that such relegation of a question is a convenient postponement of a troublesome difficulty. The use of such discussions, however, is obvious. Controversy, as Sidgwick puts it at the outset, usually implies mutual misunderstanding among thinkers. "If a thoroughly distinctive and comprehensive definition of the province of Philosophy could be worked out and universally accepted, its acceptance would mean that we were at least agreed on the questions that the philosopher has to ask, if not on the answers that ought to be given to them: and to ask the right questions is, as Aristotle saw, an important step towards obtaining the right answers" (p. 1). The want of a consensus of experts which so notoriously distinguishes philosophy from science suggests this method of approaching the subject. As he wittily puts it, "the differences of philosophical schools are so great and fundamental that it would seem to be only by a polite fiction that a philosopher of one school allows a philosopher of another school to possess philosophical knowledge on the subjects that he treats: and the politeness that consents to this fiction is not universal" (p. 6). It may be easier, therefore, to come to approximate agreement when we try to define "the knowledge we want rather than the knowledge we think we have got" (p. 13). Our definition, Sidgwick adds in the spirit of Aristotle, should be "as far as possible in conformity with common usage". He begins by provisionally accepting Spencer's well-known account of philosophy as completing the unification partially achieved by science, but states the relation more precisely thus, in accordance with the epistemological trend of modern thought: "Philosophy deals not with the whole matter of any science but with the most important of its special notions, its fundamental principles, its distinctive method, its main conclusions. Philosophy examines these with the view of co-ordinating them with the fundamental notions and principles, methods and conclusions of other sciences. It may be called in this sense 'scientia scientiarum' (p. 10). Spencer's conception of the unifying function of philosophy is, however, defective, he argues, on account of the exclusive stress which it lays on relations of identity or resemblance. A system of knowledge must explain differences as well as similarities. Thus Newton's identification of the fundamental laws of terrestrial and celestial motion explained at the same time the differences—explained, that is, why bodies fall to the earth approximately in a straight line, while planets go round the sun in
