The standard account of Kantian moral weakness fails to provide a psychologically realistic account of moral improvement. It assumes that moral strength is simply a matter of volitional resolve and weakness is a lack of resolve. This leaves the path to moral improvement unclear. In this paper, I reconstruct an alternative character-based account of Kantian moral weakness and strength. On this account, moral strength is the possession of sympathy and self-knowledge, key practical-epistemic virtues from Kant’s Doctrine of Virtue, and moral (...) weakness is a lack of these virtues. This identifies moral strength with a high degree of development, integrity, or fitness in one’s character, and not merely an ability to somehow try harder. It also resolves an exegetical puzzle concerning the change of heart in Kant’s Religion Within the Boundaries of Mere Reason. (shrink)