Homogeneity and like-mindedness are, as explanations of the social behavior of men and animals, very closely related concepts. In "like response to like stimulus," we may discern the beginning of "concerted action" and this, it is urged, is the fundamental social fact. This is the "like-mindedness" theory of society which has been given wide popularity in the United States through the writings of Professor Franklin Henry Giddings. He describes it as a "developed form of the instinct theory, dating back to Aristotle's aphorism that man is a political animal." Any given stimulus may happen to be felt by more than one organism, at the same or at different times. Two or more organisms may respond to the same given stimulus simultaneously or at different times. They may respond to the same given stimulus in like or in unlike ways; in the same or in different degrees; with like or with unlike promptitude; with equal or with unequal persistence. I have attempted to show that in like response to the same given stimulus we have the beginning, the absolute origin, of all concerted activity--the inception of every conceivable form of co-operation; while in unlike response, and in unequal response, we have the beginning of all those processes of individuation, of differentiation, of competition, which in their endlessly varied relations to combination, to co-operation, bring about the infinite complexity of organized social life.[36] Closely related, logically if not historically, to Giddings' conception of "like-mindedness" is Gabriel Tarde's conception of "imitation." If for Giddings "like response to like stimulus" is the fundamental social fact, for Tarde "imitation" is the process through which alone society exists. Society, said Tarde, exists in imitation. As a matter of fact, Tarde's doctrine may be regarded as a corollary to Giddings'. Imitation is the process by which that like-mindedness, by which Giddings explains corporate action, is effected. Men are not born like-minded, they are made so by imitation.