Until recently, most books and articles on Piaget's theory, whether laudatory or critical, were written by psychologists or, more rarely, epistemologists, who had had no direct contact with the research that provided the basis for the theoretical constructs, nor with the ongoing work on the theory itself. These authors, who looked into the theory, so to speak, from the outside, often noted aspects that were less visible to those working inside the theory and in this way raised a number of important questions. However, because most of these authors were psychologists, they often overlooked the main thrust of Piaget's work, which is epistemological. Many complained about a gap between the theory and the experimental data as reported. Such criticism may be justified, at least in part, if the theory is taken to be a psychological theory. But Piaget himself always emphasized his epistemological orientation; with this in view, the methodology of the research and its links to the conceptual framework of the theory appear in a different guise. The value of a given methodology depends on its contribution to the theory for which it was designed. The gap between theory and experiment that was frequently criticized is, in fact, the gap between the psychological and the epistemic subject.