Rudolf von Ihering was the leading German philosopher of law of the nineteenth century. He was also a major source of Weber’s more famous sociological definitions of action. Characteristically, Weber transformed material he found: in this case Ihering attempt to reconcile the causaland teleological aspects of action. In Ihering’s hands these become, respectively, the external and internal moments of action, or intentional thought and the factual consequences of action. For Weber they are made into epistemic aspects of action, the causal and the meaningful, each of which is essential to an account of action, but which are logically and epistemically distinct. Ihering thought purposes were the products of underlying interests, but included ‘ideal’ interests in this category. Weber radicalized this by expanding the category and making it historically central. This radicalization bears on rational choice theory: if ideal interests have a large historical role independent of material interests, and are not fully explicable on such grounds as ‘sour grapes’, the methods appropriate to the study of the transformation of ideas, meaning genealogies in the Nietzschean sense, are central to the explanation of action.