Kant famously insisted that “the idea of the will of every rational being as a universally legislative will” is the supreme principle of morality. Recent interpreters have taken this emphasis on the self-legislation of the moral law as evidence that Kant endorsed a distinctively constructivist conception of morality according to which the moral law is a positive law, created by us. But a closer historical examination suggests otherwise. Kant developed his conception of legislation in the context of his opposition to (...) theological voluntarist accounts of morality and his engagement with conceptions of obligation found in his Wolffian predecessors. In order to defend important claims about the necessity and immediacy of moral obligation, Kant drew and refined a distinction between the legislation and authorship of the moral law in a way that precludes standard theological voluntarist theories and presents an obstacle to recent constructivist interpretations. A correct understanding of Kant's development and use of this distinction reveals that his conception of legislation leaves little room for constructivist moral anti-realism. (shrink)