On Korsgaard's argument for Kant's moral law

Kant's formula of universal law says that it is morally impermissible to act on maxims which lead to a contradiction, when universalized. Korsgaard famously argues that we should understand the contradiction involved in Kant's formula of universal law test as practical contradiction. In her later works, Korsgaard provides an argument for the truth of Kant's moral law from the principles that are, on her view, constitutive of human agency, including the principle of publicity, the principle of universality and the hypothetical imperative. In this paper I will, first, clarify Korsgaard's argument, and, then, argue that her argument cannot vindicate Kant's moral law. More specifically, I will argue that Korsgaard's principles, contrary to what she aims, fail to occupy a middle ground between agent-neutral and agent-relative morality; for they rest upon an ambiguity in the notion of sharing the ends of other agents. As a result, Korsgaard's constitutive principles are either implausible, or too weak to be able to ground our ordinary moral obligations.