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] of human beings nor even with those of one another). Identity of ratios—of relationships—is all I can know, when I say that sensations or feelings are the same to me and to you. But, as we know, =, and yet 2 and 4, 3 and 6 are different numbers. It is because of the objectivity of the primary, as contrasted with the subjectivity of the secondary qualities of matter, that scientific men tend to regard the real world 'behind' sensible phenomena as consisting of what possesses the primary qualities only, and to endeavor constantly to translate the chaos of subjective feelings into the terms of number and measure, i.e., to turn the ordinary man's real world, that he sees, touches, smells, into a world of thought-relations. After all, however, this real world of scientific thought is a world of imagined phenomena—figures, vibrations, etc., which we should see and feel if we had keener eyes and a keener sense of touch. In either aspect the real world of science is a world that implies the presence to it of a conscious subject to make it possible. Most scientists are fond of asserting the relativity of knowledge, without perhaps taking the notion quite seriously: the more philosophical scientists admit that their atoms, molecular movements, etc., are only working hypotheses, i.e., mental constructs.

The objectivity of knowledge implies at least some degree of similarity between the mental structure of different human beings: still more obviously does the possibility of communicating knowledge imply such similarity. An epistemology, which does not wish to foredoom itself to complete scepticism, must take for granted that reality is—in some sense, that it can be known—to some extent, and that what is known can be communicated to some extent. Otherwise we may as well accept the paradoxes of Gorgias as the sum total of human wisdom. But there cannot be similarity without identity. Mere similarity is a contradictory conception. Thus we are logically driven to the conclusion that, if knowledge is possible and if knowledge is communicable, there must be some identity underlying the differences of individual human minds. The question about the minds of lower animals or of any other