Throughout his career, Jean Piaget was interested in the study of the historical development of scientific concepts. An early contribution to this field is to be seen in his inaugural lecture "Psychologie et critique de la connaissance,"¹ in which he employed what has been termed the historico-critical method. This method, used by some French philosophers of science, concerns itself with the comparative analysis of scientific concepts at different historical periods rather than at any specific one. Piaget contrasts this approach with the more a-prioristic one of Kant, for whom, he says, we know things only through the schemes and forms that our minds impose upon them. On Kant's view we find a certain number of concepts which underly all our experiences: the formal laws of logic, the notions of time, space, cause, quantity and classification, which all have a necessary character. On the other hand, the simple given or facts are the product of experience and are contingent.