Psychologists rarely concern themselves to any extent with these matters; they deal mainly with their outgrowths,--emotions, instinct, intelligence and will. We are at once beset with difficulties which are resolved mainly by ignoring them. In such a book as this we are not concerned with the fundamental nature of these divisions of the mental life, we must omit such questions as the relation of instinct to racial habit, or the evolution of instinct from habit, if that is really its origin. Again I must repeat that we shall deal with these as organic, as arising in the sensitized individual as a result of environmental forces, as manifestations of a life which is as yet--and perhaps always will be--mysterious to us. We shall best consider these manifestations of mental activity as an interplay of the reactions of stimulation, inhibition, choice, organizing energy, and not as separate and totally different matters. We shall see that probably emotion is one aspect of reaction to the world, while instinct is merely another aspect; that intelligence is a cerebral shift of instinct, and that will is no unity but the energy of instincts and purposes. Before we go farther we must squarely face a problem of human thought. Man, since he started reflecting about himself, has been puzzled about his consciousness. How can a person be aware of himself, and what identifies and links together each phase of consciousness? There is an enormous range of thought on this subject: from those who identified consciousness as the only reality and considered what the average person holds as realities--things and people--as only phases of consciousness, to those who, like Huxley, regard consciousness as an "epi-pbenomenon," a sort of overture to brain activity and having nothing whatever to do with action, nothing to do with choice and plan, so that, as Lloyd Morgan points out, "An unconscious Shakespeare writes plays acted by an unconscious troupe of actors to an unconscious audience." The first extreme view, that of Berkeley and the idealists, nullifies all other realities save that of the individual thinker and reduces one to the absurdities of Solipsism where a man writes books to convince persons conjured up by himself and having no existence outside of himself; the other view nullifies that which seems to each of us the very essence of himself.