Historic assumptions in regard to human nature, no matter how fantastic or unscientific, have exerted, nevertheless, a far-reaching influence upon group action. Periods of social revolution are ushered in by theorists who perceive only the evil in institutions and the good in human nature. On the other hand, the "guardians of society," distrustful of the impulses of human nature, place their reliance upon conventions and upon existing forms of social organization. Communistic societies have been organized upon certain ideas of human nature and have survived as long as these beliefs which inspired them controlled the behavior of members of the group. Philosophers from the time of Socrates have invariably sought to justify their moral and political theories upon a conception, if not a definition, of the nature of man. Aristotle, in his _Politics_ and Hobbes in his _Leviathan_, to refer to two classics, offer widely divergent interpretations of human nature. Aristotle emphasized man's altruistic traits, Hobbes stressed his egoistic disposition. These opposite conceptions of human behavior are explicit and in each case presented with a display of evidence. Yet students soon realize that neither philosopher, in fashioning his conception, is entirely without animus or ulterior motive. When these definitions are considered in the context in which they occur, they seem less an outgrowth of an analysis of human nature, than formulas devised in the interest of a political theory. Aristotle was describing the ideal state; Hobbes was interested in the security of an existing social order. Still, the contribution made by social and political philosophers has been real. Their descriptions of human behavior, if inadequate and unscientific, at least recognized that an understanding of human nature was a precondition to social reorganization. The fact that philosophical conceptions and ideal constructions are themselves social forces and as such frequently represent vested interests, has been an obstacle to social as well as physical science. Comte's notion that every scientific discipline must pass through a theological and metaphysical stage before it assumed the character of a positive science seems to be true as far as sociology is concerned. Machiavelli shocked the moral sense of his time, if not the moralists of all time, when he proposed to accept human nature as it is as a basis for political science. Herbert Spencer insisted upon the futility of expecting "golden conduct from leaden instincts." To the utopian social reformers of his day he pointed out a series of welfare measures in England in which the outcome was the direct opposite of the results desired.