Or we may put the case in another way. The whole process of scientific systematisation involves certain assumptions as to the ultimate nature of the facts which are systematised. Thus the very performance of an experiment for the purpose of verifying a suggested hypothesis involves the assumption that the facts with which the hypothesis is concerned conform to general laws, and that these laws are such as to be capable of formulation by human intelligence. If “nature” is not in some sense “uniform,” the conclusive force of a successful experiment is logically _nil_. Hence the necessity for an inquiry into the character of the presuppositions involved in scientific procedure, and the amount of justification which can be found for them. For practical purposes, no doubt, the presuppositions of inductive science are sufficiently justified by its actual successes. But the question for us as metaphysicians, as we have already seen, is that not of their usefulness but of their truth. It may be said that the inquiry ought in any case to be left to the special student of the physical and psychological sciences themselves. This, however, would involve serious neglect of the great principle of division of labour. It is true, of course, that, other things being equal, the better stored the mind of the philosopher with scientific facts, the sounder will be his judgment on the interpretation and implications of the whole body of facts. But, at the same time, the gifts which make a successful experimentalist and investigator of facts are not altogether the same which are required for the philosophical analysis of the implications of facts, nor are both always conjoined in the same man. There is no reason, on the one hand, why the able experimenter should be compelled to desist from the discovery of facts of nature until he can solve the philosophical problems presented by the very existence of a world of physical facts, nor, on the other, why the thinker endowed by nature with powers of philosophical analysis should be forbidden to exercise them until he has mastered all the facts which are known by the specialists. What the philosopher needs to know, as the starting-point for his investigation, is not the specialist’s facts as such, but the general principles which the specialist uses for their discovery and correlation. His study is a “science of sciences,” not in the sense that it is a sort of universal encyclopædia of instructive and entertaining knowledge, but in the more modest sense of being a systematised reflection upon the concepts and methods with which the sciences, and the less methodical thought of everyday practical life work, and an attempt to try them by the standard of ultimate coherence and intelligibility.