How do we determine whether an action is right or wrong? Until recently, philosophers assumed that this question could be answered by means of a theory of morality, which set forth clearly established rules for moral behaviour. More recently, however, a number of philosophers have challenged a theory of morality in this sense. Porter is sympathetic to their criticisms but questions whether they go far enough in offering a positive alternative to a modern view of the moral act. She argues that the work of Aquinas offers an alternative account of moral rationality, in terms of which moral reasoning is understood as dialectical rather than deductive, and questions are resolved in a wider context of ethical thought. Aquinas's account of the moral virtues and prudence is seen to offer unexpected insights into the relationship between moral rules and the practice of the virtues, thus contributing to our own moral reflection.