The first experience must have come to man very early in his development. As soon as any act was proscribed and punishment meted out for its performance, or as soon as a reward was consciously sought—though its attainment necessitated realised, personal danger—there must have been a deliberate, conscious inhibition of natural desires, which in its turn enforced a similar restraint of muscular, physical functioning. As the needs of society widened, this necessity for the daily, hourly inhibition of natural desires increased to a bewildering extent on the prohibitive side. There grew up first “taboos,” then the rough formulation of moral and social law, and on the other hand a desire for larger powers which encouraged qualities of emulation and ambition. Among the infinite diversity of these influences, natural appetites and the modes of gratifying them were ever more and more held in subjection, and the subconscious self or instinct which initiated every action in the lower animal world fell under the subjection of the conscious, dominating intellect or will. And in this process we must not overlook one fact of supreme importance, viz., man still progressed physically and mentally. It is therefore clear that this control acquired by the conscious mind broke no great law of nature, known or unknown, for, if this acquired control had been in conflict with any of those great, and to us as yet incomprehensible forces which have ruled the evolution of species, the animal we call man would have become extinct, as did those early saurian types which failed to fulfil the purpose of development and perished before man’s first appearance on this earth. Before we attempt, then, any exact definition of the subconscious self we must have a clearer comprehension of the terms “will,” “mind,” and “matter,” which may or may not be different aspects of one and the same force. More than two thousand years of philosophy have left the metaphysicians still vaguely speculating as to the relations of these three essentials, and personally, I am not very hopeful of any solution from this source. The investigation, though still in its infancy in this form, has taken the shape of an exact science, and it is to that science of psychology as now understood that I look to the elucidation of many difficult problems in the future. Without touching on the uncertain ground of speculative philosophy, I will try, however, to be as definite as may be with regard to my conception of the subconscious self.