All the concepts that are referred to here: purpose, co-ordination, inhibition and will, are every one of them dependent upon one fundamental concept, consciousness. Without it they are unthinkable. Schopenhauer's unconscious will is a word without meaning. I have postulated consciousness as the inseparable concomitant of life. It is probably the essence of life. In its lowest stage it is too dim, its contents too meagre and blurred, properly to distinguish the organism in which it dwells from the world around. In a higher state of development, when it gradually grows clearer and begins to be filled with more sharply defined ideas, it learns to keep its organism and the surrounding world apart, and tries to make the attitude of the former to the latter one of self-defence, self-preservation and self-development. From this stage of development onward, concepts begin to connect and group themselves in such a way that consciousness contains not only an image of the immediate present, but also memories of the past and a forecast of the future. The ability to prolong the present into the future, to understand the actual as a cause of the effects that follow and to foresee these effects, that is the starting point of logic and reason. It is the necessary antecedent of the will, which would have no meaning if it were not the effort to realize a conception of actions and their consequences, previously worked out by consciousness. Will is a function of consciousness which, in pursuance of the well-known biological law, creates an instrument for its purposes, and this instrument is inhibition. The higher an organism stands on the ladder of evolution the more energetically and surely does inhibition work, the nicer and the more masterly does its intervention in the original reflex actions grow.