Recently, Christine Bratu and Mortiz Dittmeyer have argued that Christine Korsgaard’s constitutive project fails to establish the normativity of practical principles because it fails to show why a principle’s being constitutive of a practice shows that one ought to conform to that principle. They argue that in many cases a principle’s being constitutive of a practice has no bearing on whether one ought to conform to it. In this paper I argue that Bratu and Dittmeyer’s argument fails in three important (...) respects. First, they fail to recognize the ways in which Korsgaard’s neo-Kantian view departs from more orthodox Kantian views. Second, they fail to recognize the respect in which Korsgaard’s view is a version of moral rationalism. Third, they overlook an important scope ambiguity in an important premise of their argument. A sensible way of resolving this ambiguity gives the constitutivist a reasonable response. (shrink)