are for nominalistic science simply general terms denoting the three groups of mental phenomena which seem to stand off most clearly and fundamentally from each other, and Pleasure and Pain are most clearly and fundamentally set over against Knowing and Willing. It does not seem that Professor Bain and others have made plain to us any better differentia. If this definition of Feeling seems the best that descriptive classification can give us, it is certainly enforced by genetic considerations. The key to a really scientific classification lies in the history of mind in the individual and race. The greatest progress in psychology is not to be attained by the psychologist continually reverting to his own highly developed consciousness, but, as in all sciences, the study of the simple must be made to throw light upon the complex. Mentality like life is a body of phenomena whose forms cannot be separated by hard and fast lines into orders, genera, species; but there is a continuous development of radical factors. In the earliest forms of mind we find the most radical distinctions most clearly and simply set forth, and what Feeling is at first, it is by continuity of development the same for ever after. The earliest indications of conscious life show merest trace of apprehension of object, some organic pleasure and pain, considerable striving and effort. Mental evolution, like all evolution, is not by the elimination but by the expansion of its primal factors; and by the continuous amplification and intensification of these the highest development is reached. Pleasure and pain remain then for all consciousness as constant factors; and if the term Feeling is to indicate one element in tripartite mind, it must be held to this meaning of pleasure and pain. Pleasure and pain in their most complicated colourings from developed knowledge and will, and in their most subtle interactions, remain true to the primal type; and when we find a state of consciousness in which neither is a dominant factor, we had best denote it by some other term than Feeling. This evolutionary reason seems to me the strongest one for making the term Feeling signify states of pleasure or pain, and, as I have suggested (_Mind_, xi. 74-5), a genetic classification of the feelings must proceed upon this basis. CHAPTER V _EARLY DIFFERENTIATION_