IN every age philosophy has been affected by the sciences, ie, the methods and conceptions which are used in the attempt to make some particular province or aspect of the universe intelligible have exer-cised a fascination over those who are seeking to understand the universe as a whole. And this is only natural: for the philosopher, who is really the philosopher of his own age and not the survival from an earlier epoch, is the prodact of the same intellectual movement which has led to the adoption of new methods and new conceptions among those who are pursaino special branches of knowledge. The difference between the genuine philosopher and the average seeker for" completely unified knowledge" is that the former has a fuller and clearer consciousness of the methods and conceptions he is using, and is less likely to apply them uncritically and in disregard of the subject-matter to which he is applying them. Mathematics was the only science that had outgrown the merest infancy among. the Greeks. And in the Pythagoreans we have an example of philosophers who were completely carried away by the fascination of the conceptions of number and figure. In defining justice as" a square number" the Pythagoreans were for the first time attempting to make ethics" scientific," ie, to lift reflection on human conduct out of the region of proverbial moralising by applying to it the most scientific categories of which they knew. Plato has puzzled many generatious of commentators by those mystic numbers which he introduces into his philosophy; in all likelihood he only half believed in them (if so much as that), and he seems to be playing an elaborate and rather cruel joke on literal-minded persons, hint. ing all the while at the inadequacy of the Pythagorean symbols. Aristotle introduced mathematical formula into ethics, but only with carefully expressed modifications. His conception of scientific method comes, indeed, too exclusively from mathematics; but he is in advance of many modern moralists in seeing that buman conduct at least is too complex to be studied by mathematical methods. It might be objected, that in mediaeval philosophy the principle I have laid down did not hold, but that the reverse was the case, that philosophy was not affected by the sciences, but that the sciences were" Ccorrupted by metaphysics." The study of nature, however, was by no means that on which the medieval intellect exerciscd itself. There were in truth only two" sciences" in which the medieval mind