In this first volume of a projected trilogy, the author argues that a methodology adequate to solve the long-standing debate over the status of the social as against the natural sciences can be constructed in terms of a fourhold distinction between the reportage, explanation, description and evaluation of human behaviour. The distinction rests on an analysis of the scope and nature of social theory which is not only original in conception but far-reaching in its implications for the assessment of the results of sociological, anthropological and historical research. In this volume, there are set out the separate and distinctive criteria by which the reports, explanations, descriptions and evaluations put forward by social scientists of rival theoretical schools require to be tested. These criteria will then be applied in Volume II to a substantive theory of social relations, social structure and social evolution, and in Volume III to a detailed analysis of the society of twentieth-century England. Each of the three volumes can be read independently of the others. But the trilogy will, when completed, be seen to form a coherent and unified whole.