of facts and the detailed working out of the application of the principles to the facts.  For convenience’ sake it will be well that some of us shall be engaged on the discovery of principles which are so very ultimate that most men take them for granted without reflecting on them at all, and others on the work of detail.  Further, it will be convenient that, within this second group, various students shall give their attention to more special masses of detail, according to their several tastes and aptitudes, some to the behaviour of moving particles, some to the behaviour of living organisms, some again to the structure and institutions of human societies, and so on.  For convenience we may agree to call preoccupation with the great ultimate principles Philosophy and preoccupation with the application of the principles to masses of special facts Science.  If we make the distinction in this way, we shall be following pretty closely the lines of historical development along which ‘special’ sciences have gradually been constituted.  When we go back far enough in the history of human thought, we find that originally, among the great Greeks who have taught the world to think, there was no distinction at all between Science and Philosophy.  Men like Plato and Aristotle were busied at once with the discovery of the first principles on which all our knowledge depends and with the construction of a satisfactory theory of the planetary motions or of the facts of growth and reproduction.  As the study of special questions was pursued further, it became advisable to hand over the treatment of first one and then another group of closely interconnected questions to students who would pursue them independently of research into ultimate presuppositions.  This is how Geometry, Astronomy, Biology came, in ancient times, to be successively detached from general Philosophy.  The separation of Psychology—­the detailed study of the processes of mental life—­from Philosophy hardly goes back beyond the days of our fathers, and the separation of such studies as ‘sociology’ from general Philosophy may be said to belong quite definitely to our own time.  If our children have leisure for study at all, no doubt they will see the process carried much further.  But it is important to bear in mind that neither Philosophy in the narrower sense nor Science in the narrower sense will be fruitfully prosecuted unless the men who are working at each understand that their own labours are only part of a single undivided work.  Without a genuine grasp of some department of detailed facts no man is likely to achieve much in the search for principles, for it is by analysis of facts that principles are to be found, and without real insight into broad general principles the worker in detail is likely to achieve nothing but confusion.  The antagonism between ‘philosophers’ and ‘men of science’ so characteristic of the last half of the nineteenth century has been productive of nothing but evil.