ABSTRACT. Hume and Kant disagree about the motives involved in the performance of our duties to others. Hume thinks that natural virtues such as benevolence are best performed from “natural” motives, but that there are no natural motives for the performance of the “artificial” virtues, such as justice and fidelity to promises, which are performed from a sense of duty. Kant thinks all duties should be done from the motive of duty. In this paper, I examine the roots of the disagreement. If by a natural motive Hume means an intention that can be described without using normative concepts, Kant would deny that any adult human motives are “natural,” for all involve the thought that something is a reason. But Hume also seems to imply that being motivated to benevolence and self-interest is “natural” in some way that being motivated to keep our agreements is not. I trace this difference to differences in the two philosophers’ conceptions of action. Hume’s conception of action does not allow for genuinely shared action, while Kant’s does. For Kant, being motivated to keep our agreements is just as natural as being motivated to do others good. (pp. 8–35)