Modern philosophy has been vexed by the question “Why should I be moral?” and by doubts about the rational authority of moral virtue. In Reasons without Rationalism, Kieran Setiya shows that these doubts rest on a mistake. The “should” of practical reason cannot be understood apart from the virtues of character, including such moral virtues as justice and benevolence, and the considerations to which the virtues make one sensitive thereby count as reasons to act. Proposing a new framework for debates about practical reason, Setiya argues that the only alternative to this “virtue theory” is a form of ethical rationalism in which reasons derive from the nature of intentional action. Despite its recent popularity, however, ethical rationalism is false. It wrongly assumes that we act “under the guise of the good,” or it relies on dubious views about intention and motivation. It follows from the failure of rationalism that the virtue theory is true: we cannot be fully good without the perfection of practical reason, or have that perfection without being good. Addressing such topics as the psychology of virtue and the explanation of action, Reasons without Rationalism is essential reading for philosophers interested in ethics, rationality, or the philosophy of mind.