The distinguished Columbia University historian Richard Hofstadter possessed a scholarly imagination unusually open to fresh approaches to illuminating the past. In the seven years that separated the publications of "American Political Tradition" (1948) and "The Age of Reform" (1955), Hofstadter absorbed new intellectual insights that challenged the Progressive assumptions of his graduate training and borrowed heavily from modern social theory. This involved an effort not merely to reconstruct the course of political and economic transformation but also to recover the mental cultures that shaped and gave meaning to change. It presumed that collective psychology and seemingly irrational pressures provoked responses by historical actors that could not be explained by traditional research strategies. This article shows how, while under the spell of the social sciences, Hofstadter produced the most creative and controversial work of his impressive career. (Contains 54 notes.)