 The fundamental assumption that ties enforcing rights and obligations to institutional practice serves to fix the subject matter of inquiry by setting the interpretive problem. Notice however that it does not rise to a conceptual constraint as these are normally understood. For the theory treats it as a commonly held moral hypothesis about the normative relevance of institutional practice. As a substantive hypothesis it is not immune to doubt but is subject to critical scrutiny. It would remain possible coherently to reject the assumption as mistaken, as long as an alternative hypothesis could make intelligible other common pre-theoretical commitments. The doctrine that Dworkin (1986) calls “pragmatism” illustrates this possibility, since it rejects the dependence of permissible enforcement on legality as defined above, and recommends instead that claims of obligation be enforced when doing so is justified by forward looking considerations. For the pragmatist, the claims’ relation to institutional practice is to be invoked merely for strategic purposes. We might say that the assumption that connects enforcement to institutional practice fixes but does not determine the subject matter of legal theory.  Moreover, the basic assumption does not by itself entail an answer to the interpretive problem that it sets. That is the problem of constitutive explanation with which we began: how institutional practice figures in the constitutive determination of legal rights and obligations.