There are basically two approaches to a study of the development of ideas in a discipline. The first concentrates on the dialectical sequence of change in the theories, concepts and analytical techniques which constitute the substance of the discipline; the second traces the historical process of change in the way successive generations of scientists have adapted their explanatory techniques to a solution of the problems they regarded as important and soluble. The two approaches are not mutually exclusive, they overlap, and most historians of economic thought have taken both into account. But they raise different sets of questions. The approach from the first aspect is primarily concerned with a rational justification and critique of the theoretical basis of economic analysis in successive epochs; the second with explaining the historical process of innovation and adaptation in the analytical framework which economists have typically accepted as appropriate to the pursuit of their enquiries. The predominant trend in recent histories of economic thought has been towards increasing the emphasis on the first approach. Schumpeter's History of Economic Analysis and Blaug's Economic Theory in Retrospect are among the more widely known examples of the genre. This book, mainly intended for students committed to a systematic study of economic theory, shifts the weight of its emphasis in the direction of the second approach and seeks to interpret the history of economic thought as a process of change in the ideas of successive generations of economists.