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No. 3.] conditions under which it acts. While Professor Ladd and the metaphysicians are telling us what the soul is, how shall we learn the conditions under which it acts, save by a study of the relations between brain-processes and mental states? Surely metaphysics and natural-science psychology have no right to regard each other as rivals. Possibly Professor Ladd is right when he says that natural-science psychology cannot solve her problem. But if so, he must admit that we can never know what we must know in order to have a complete knowledge of mental phenomena. Perhaps the Positivists are right when they say that we can never comprehend the metaphysical ground of mental phenomena, that we cannot even know that there is such a ground. But if so, they must admit that the ultimate laws of psychology will be only blank correspondences stupidly standing out from a background of impenetrable darkness. But whether the problems of one or both is insoluble, they are at any rate different, and each has a perfect right to attempt the solution of its problem until the solution is proved to be impossible.

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OHIO UNIVERSITY.