In The Possibility of Altruism Thomas Nagel introduces a distinction between motivated and unmotivated desires that has since become standard in discussions of action theory and moral psychology. But what, exactly, are these categories? Many uses of the term, arguably including Nagel’s own, treat a desire as unmotivated if one has no reason for it. So conceived, unmotivated desires are mere urges, whims or unintelligible dispositions. It would be out of place to ask an agent to justify these states in the same way that it would be out of place to demand reasons for a headache. But Nagel introduces the idea differently, calling a desire unmotivated if one does not reason to it, that is does not engage in explicit practical reasoning resulting in the motivation to act.