The nature of psychology, however, and the nature of philosophy, and especially the nature of the relations existing between the two, are such as to make it undesirable, if not impossible, to consider in one book all the metaphysical prob lems which this empirical science suggests. Indeed, the whole sphere of philosophical studv scarcely does more than this. A somewhat but not wholly arbitrary selection of problems had, therefore, to be made; and their detailed dis cassion was then brought under the one title, Philosophy of Mind. The reasons for the selection are made sufficiently clear in the course of the discussion itself.