What is the ego that desires and plans? I do not know, but if it is in any part a metaphysical entity of permanent nature in so far it does not become the subject matter of this book. For as a metaphysical entity it is uncontrollable, and the object of science is to discover and utilize the controllable elements of the world. I may point out that even those philosophers and theologians to whom the ego is an entity of supernatural origin deny their own standpoint every time they seek to convince, persuade or force the ego of some one to a new belief or new line of action; deny it every time they say, "I am tired and I shall rest; then I shall think better and can plan better." Such a philosopher says in essence, "I have an entity within me totally and incommensurably different from my body," and then he goes on to prove that this entity operates better when the body is rested and fed than otherwise! For us the ego is a built-up structure and has its evolution from the diffuse state of early infancy to the intense, well-defined state of maturity; it is elaborated by a process that is in part due to the environment, in part to the inherent structure of man. We may postulate a continuous excitement of nerve centers as its basis, and this excitement cognizes other excitement in some mysterious manner, but no more mysterious than life, instinct or intelligence are. These excitements struggle for the possession of an outlet in action, and this is what we call competing desires, struggle against temptation, etc. Sometimes one desire is identified with the ego as part of itself, sometimes the desire is contrasted with the ego and we say, "I struggled with the desire but it overcame me." Common language plainly shows the plurality of the personality, even though the man on the street thinks of himself as a united "I," even an invisible "I." One of the fundamental desires, nay the fundamental desire, is the expansion of the self, i. e., increased self-esteem. When the infant sprawls in his basket after his arrival in this world, it is doubtful if he has a "me" which he separates from the "non-me." Yet that same infant, a few years later, and through the rest of his life, believes that in his personality resides something immortal, and has as his prime pleasure the feeling of worth and growth of that personality, and as his worst hurt the feeling of decay and inferiority of that personality.