Chapter 4 will be devoted to a systematic discussion of the interpretivist claims about legal obligation. After introducing the basic elements of the interpretivist account of law and legal obligation, I pass to critically assess whether interpretivism has the conceptual resources necessary to make full sense of legal obligation as a distinctive notion. In this context, I will focus on what I take to be the fundamental problem besetting the interpretivist theory of legal obligation. This problem can be summarized as follows. The account defended by interpretivism presents legal obligations as duties fundamentally determined by the political morality underpinning a given institutional practice. This claim establishes no conceptual connection between what is legally obligatory and what is required by critical morality understood as a scheme of normative standards warranted by practical rationality. The problem with this statement is that, on the interpretivist account, the fundamental principles of rational morality are not necessarily regarded as components of legal obligation. And insofar as that is the case, the interpretivist account allows for the possibility that legal obligations diverge from obligations grounded in practical rationality, while at the same time qualifying them as genuine obligations