In this paper Bloch is concerned to specify rea- sons for the perennial difficulty that anthropolo- gists have had in formulating an adequate theory of social change. Bloch points out that the con- cept of social structure in anthropology refers essentially to an integrated totality of social classifications and meanings, a system of social rules and roles which can, in one widely accepted anthropological sense of the term, be called ritual. Now if this concept of social structure is linked to the doctrine of the social origin of concepts (the social determination of cognition) it becomes impossible to specify how social change can occur. This is because, so Bloch argues, a system of meaningful categories, of shared concepts that makes communication possible (a system which is none other than social structure) cannot explain the creation of new concepts.