  Pure interpretivism offers a thoroughly moral explanation of the normative relevance of institutional practice, by identifying a moral concern that gives the practice in the abstract such relevance. It characteristically begins at some familiar, structural features of legal practice, whose existence is usually tacitly assumed. The first concerns the institutional character of law.  It’s an unspoken fundamental assumption in law that claims of legal right or obligation are claims grounded, in some appropriate way, in past institutional decisions and standing practices of government—in actual not ideal institutional arrangements—and that only claims so grounded shall be recognized and enforced. Call that kind of grounding the legality of a claim. The second concerns the role that the legality of a claim is supposed to play in relation to some moral concern. It is not merely uncharacteristic but also impermissible for legal institutions to enforce some claim against a person, unless the claim meets the conditions of legality by being appropriately grounded in institutional practice.