This chapter asks where Kant stands on one of the most famous contentions of ancient ethics: the so-called Unity of the Virtues, the claim that a person who has one of the virtues must have all of them. The twentieth-century revival of virtue ethics was partly prompted by explorations of this proposal – its centrality to ancient theories and its presumed implausibility for philosophers today. Kant announces that he rejects three ancient premises about virtue, the first of which is “there is only one virtue and one vice”. The chapter argues that he thereby rejects the Unity of the Virtues, as the Stoics conceive of it. For Kant, virtue-singular is prior to virtues-plural, but it is not one. The virtues-plural are not parts of virtue; the latter is not a whole in the way the Stoics take it to be. Nevertheless, Kant shares more with the ancients than with twentieth-century philosophers writing on the topic. He endorses the premise that virtue-singular is prior to the virtues-plural.

Kant and the Stoics both rely on a momentous argument, set out in Plato’s dialogues, for the conclusion that nothing is unconditionally good but wisdom, yet they differ on how to interpret it. The Stoics identify this wisdom with the perfection of technical or productive knowledge of nature, and they regard it as the sole good. Kant identifies this wisdom with the perfection of practical knowledge of the good, and, analyzing this knowledge along the hylomorphic lines implicitly suggested in Plato’s argument, he locates wisdom’s unconditional goodness – its morality, or moral goodness – in its agreement not with the object it produces but with its form, morality’s principle. Two contrasting accounts of morality’s relation to perfection thus emerge. The Stoics see perfection in the knowledge of nature as entailing moral goodness, whereas Kant argues that moral goodness is the condition of all other goodness, including that of perfection.