Duties to oneself are central to Kant’s moral thought. Indeed, in his Lectures on Ethics, he claims that they “take first place, and are the most important of all” (27:341). Despite this, Kant is not clear about what they are or why they are ‘the most important.’ What is it for a duty to be owed to oneself? And in what sense do such duties ‘take first place’? I answer these questions: a duty to oneself is a self-legislated duty, and they ‘take first place’ in that all ethical duties are, fundamentally, duties to oneself. Based on a close reading of Kant’s “Apparent Antinomy” regarding duties to oneself in The Doctrine of Virtue §§1–3, I argue that Kant holds that (1) a duty is owed to its legislator, and (2) all duties are self-legislated. I then argue that this interpretation is further supported by Kant’s understanding of the Categorical Imperative as a “principle of autonomy” in the Groundwork (4:433). I conclude by offering an interpretation of the Categorical Imperative on which even though all duties are ultimately owed to oneself, there remains an important sense in which some duties are owed to others as well.

We articulate and defend the most central claims of contemporary Kantian moral theory. We also explain some of the most important internal disagreements in the field, contrasting two approaches to Kantian ethics: Kantian Constructivism and Kantian Realism. We connect the former to Kant’s Formula of Universal Law and the latter to his Formula of Humanity. We end by discussing applications of the Formula of Humanity in normative ethics.