Rethinking Kant on Duty

According to a common caricature, Kant’s ethics is synonymous with the categorical imperative (CI) and with the sublime and clarion call of duty. But for reasons frequently overlooked in modern scholarship, the conjunction of Kant’s concept of duty and his idea of morality as a system of imperatives is unsustainable, and this has implications for various central aspects of his thought including “ought implies can” (OIC), “ought implies able not to” (OIAN), his system of duties, and the nature of respect.

This article is divided into five sections. In the first I explain Kant’s concept of duty and his distinction between the Supreme Law of Morality and the CI. I argue that Kant is committed to the following conjunctive claim:

1. I. If an agent has a duty to D, then he must be constrained to D, and

2. II. the Supreme Law of Morality always manifests in the form of duty for humans (and other imperfectly rational beings).

In the second, third, and fourth sections I examine various ways in which this claim might be defended. I argue that these defenses are all flawed. By way of preview, in section 2 I examine the following defense: There is an end M such that for all duties D, M and D are opposed. I argue that there are textual grounds for ascribing this defense to Kant (with happiness as M) but that, ultimately, this defense is both exegetically and philosophically unsustainable.

In section 3 I then turn to this defense: For all duties D there is an inclination M such that M and D are opposed. I examine a strong version and a weak version of this defense. On the strong version, M is an inclination to perform some action other than D. On the weak version, M might be an inclination to perform D, but constraint is nonetheless necessary for an agent to perform D from duty. I argue that the strong version is too strong (it is philosophically unsustainable) and that the weak version is too weak (it undermines the original conjunctive claim it was supposed to defend).

In section 4 I turn to Kant’s doctrine of radical evil and argue that it, too, cannot be used to defend this conjunction. In the fifth and final section I explore some of the implications of the preceding. In particular, I maintain that (a) either the Kantian version of OIC does not have universal scope, or ought does not imply constraint; (b) OIAN does not have universal scope; (c) our conception of the kinds of duties we get on Kant’s account needs to be reconceived; and (d) the nature of respect as a moral feeling needs to be reconceived.

I

Duty and the Categorical Imperative

Kant introduces the concept of duty in part 1 of the Groundwork of the Metaphysics of Morals: “[T]he concept of duty . . . contains that of a good will, although under certain subjective limitations and hindrances.” ¹ This is echoed about forty pages later in part 2 of the text:

The dependence of a not absolutely good will on the principle of autonomy (the moral necessity) is obligation. This can thus not be extended to a holy being. The objective necessity of an action from obligation is called duty.²

Notwithstanding their brevity, these two passages tell us a lot about Kant’s commitment to OIC and OIAN. Kant’s commitment to OIC follows from the claim that the concept of a good will is contained in that of duty. In particular, this claim entails that an agent has a duty to A only if he actually would A if he had a good will in that instance, whence it is supposed to follow that an imperfectly rational agent, one who is able to act in accordance with reason although he might not always do so, is able to A.

Moreover, because this is a claim about concept containment, it follows that, according to Kant, OIC is an analytic truth: the “implies” in OIC is strict logical entailment (rather than, say, metaphysical entailment or conversational implicature).

Kant’s commitment to...