Based on a comparative study of the theories of such sociologists as Ward, Sumner, Keller, Giddings, Ross, Small and Cooley, this is a systematic and rigorous analysis of the main features of earlier sociological theory in the USA. The author identifies and characterizes the basic assumptions of early American sociological thought in terms of an abstract analytical scheme. He shows that early theory focused on social ontological interests, the pervasive ontological stance being evolutionary naturalism, within which the problems of social origins and social change tended to be paramount. He also points out that some sociologists preferred a social process theory. In his final chapter the author suggests the degree of similarity and dissimilarity, of continuity and discontinuity, between earlier and later theory in American sociology, and provides a basis for explaining and interpreting the character of the prevalent assumptions of one period in American theory in relation to other periods.