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.
A blind psychic life of pure feeling cannot long avail in the sharp struggle of existence, for to all stimulations it secures only two crude reactions, a spasmodic, defensive activity from pain, and an appropriative motion from pleasure. This perfectly subjective consciousness can serve only the earliest and crudest demands of life; but as the struggle for existence becomes fiercer, the more delicate and definite reactions, which can only come through cognition, are required. All that we can say as to the origin of knowledge in general is that it arose, or rather was achieved, like other conscious and extra-conscious functions, in answer to the pressing demands of the organism; and so far as we can see, it does not seem to be evolved from any pre-existing consciousness or any common basis of mind. It is a distinct type of consciousness, and so utterly diverse that we cannot trace any psychical continuity. However, we can remark this,—that perfect objectifying is not at once achieved, but cognition must be regarded as beginning in a very minute and obscure germ in some intense feeling state. Yet this germ does not seem to have a direct psychical connection with the pure feeling by which it is excited into existence, but it is a reaction to an opposite mode more diverse from pleasure and pain than these are from each other. Moreover, according to the law of evolution by struggle, this first cognition does not _come_ to mind, but is _achieved_ only in most intense will act, comparable for relative intensity to the knowledge originated by severest effort of a man in danger of his life listening to a barely audible sound, or watching a barely visible object on a distant horizon. The evolution point for all life is in stress and strain, and this is the law of the development of sensation at all times in psychic history.[A]