The subject is not likely to interest anyone who does not care for the study of the exact definitions and abstract principles that lie at the basis of science and philosophy. There are many who are engaged in the study of the physical and natural sciences, and also many who devote themselves to the social and political {12} sciences, who hold in profound contempt the fine distinctions and intellectual subtleties that seem to them the whole content of logic and metaphysic. The attitude of the scientific mind is not difficult to understand. It has recently been rather graphically expressed by a distinguished and popular exponent of the principles of natural science. "One may regard the utmost possibilities of the results of human knowledge as the contents of a bracket, and place outside the bracket the factor _x_ to represent those unknown and unknowable possibilities which the imagination of man is never wearied of suggesting. This factor _x_ is the plaything of the metaphysician."[1] This mathematical symbol of the bracket, multiplied by _x_ to represent the unknown and unknowable possibilities beyond it, will serve me to indicate with some exactness the problem with which I am going to deal. The symbol is an expression of the agnostic position. The popular caricature of the metaphysician and his "plaything" we may disregard as a pure fiction. The unknowable _x_ of the agnostic is not the "meta" or "beyond" of physics which the metaphysician vainly seeks to know. The only "beyond" of physics is consciousness or experience itself, and this is the subject-matter of metaphysics. Our present problem is that of the bracket, not that of the factor outside, if there is any such factor, nor yet the particular nature of the contents within. There are, as we shall see, three views that are possible of the nature of the bracket. In one view, it is merely the conception of the extent which knowledge has attained or can attain; it has no intimate relation to the knowledge, but marks externally its limit. This is the view of the realist. In another view, the whole of knowledge is intimately related {13} to its particular parts; the things we know are not a mere collection or aggregate of independent facts that we have discovered; the bracket which contains our knowledge gives form to it, and relates organically the dependent parts to the whole in one comprehensive individual system. This is the view of the idealist. There is yet another view: human knowledge is relative to human activity and its needs; the bracket is the ever-changing limit of that activity--within it is all that is relevant to human purpose and personality without it is all that is irrelevant. This is the view of the pragmatist.