By way of preface it might be said that a good deal of the confusion as to the subject matter of social psychology would be avoided if it were understood that this science is not the study of any mysterious entity called ‘the social mind,’ nor the mere study of those individual traits that make men social beings, such as imitation and suggestibility; but rather the study of the peculiar and characteristic behavior of the mind of the individual when under the influence of the social afflatus. Under this influence we do indeed find that he becomes a different being, and that his mental processes must be formulated by different laws; and we are convinced that, as thus understood, social psychology is just as distinct and legitimate a branch of study as is the psychology of the child or the psychology of sex. Now, in what ways is the behavior of man as a social being different from his behavior as an individual? To answer this question in part, let us examine his behavior in mental epidemics and crazes. I select these because they illustrate in somewhat extreme form the influence of the social afflatus. If, for the sake of comparison, we first consider the normal individual as such, we find that he is a perceiving, remembering, associating, judging, reflecting, reasoning being; that he is subject to certain feelings, emotions, desires and impulses, prompting him to action; that his action is more or less deliberative, and, when it finally occurs, is the result of a set of motives determined by the man’s character, which in turn is the outcome of his heredity and education and his general ability to appreciate and reflect the moral ideals of the social order to which he belongs. If now we study this man in respect to his mental development, whether from the savage or the child, we find that the direction of change has been away from imitative, impulsive action, towards thought, reflection, deliberation. He continually makes more use of memory and, anticipating the future, regulates his action in the light of his past experience. This change from the imitative and impulsive to the reasoning man accompanies the development of the higher brain centers, particularly of the cerebral cortex, upon which depend the all-important functions of memory and association. As an experiment it is quite possible to reduce this highly developed reasoning being in a single moment to a condition resembling his primitive state by means of hypnotism. In hypnosis there is a temporary paralysis or sleep of the higher brain centers, upon which depends deliberative, rational action, and, the lower (older) centers alone being active, the subject becomes a mere ideo-motor machine acting out every suggestion. In various related states of automatism, where there is any spontaneity at all, the mentality and morality of the subject are of a lower type and may be called reversionary in character, owing, no doubt, to the fact that those