By sketching a major development in the history of French sociology, I wish to illustrate a general method for understanding the history of social-scientific thought. The increasingly common separation between subdisciplines, like the history of intellectuals and the history of ideas or the sociology of scientists and the sociology of scientific knowledge, makes unlikely a satisfactory explanation of either member of such dichotomized pairs, for each is necessary to understand the other. These unwarranted distinctions stem from the tremendous difficulties of showing precise causal relationships in either direction, though most would admit that important links between them exist. For example, the problems with showing how a given socio-political milieu articulates with a specific idea or how certain patterns of scientific research organization led to particular scientific discoveries (not just to a greater or lesser number of "innovations") have caused many to abandon the effort. The method offered in this paper is meant to bridge the gap between so-called "external" and "internal" modes of analysis. Since the worth of a method lies in its application, I shall devote most of my explicit remarks to a single illustrative case -the