In recent work, Martha Nussbaum has exposed an important ambiguity in the standard conception of political liberalism. The ambiguity centers on the notion of "reasonableness" as it applies to comprehensive doctrines and to persons. As Nussbaum observes, the notion of reasonableness in political liberalism can be construed in a purely ethical sense or in a sense that combines ethical and epistemic elements. The ambiguity bears crucially on the respect for persons norm—a key norm that helps to distinguish political from perfectionist versions of liberalism. Nussbaum contends that when political liberals affirm a construal of reasonableness that includes epistemic elements they run into trouble in formulating an account of their view that sharply distinguishes it from perfectionist liberalism. She contends further that perfectionist versions of liberalism should be rejected since they fail to offer an account of respect for persons. This paper responds to Nussbaum’s challenge. It argues that an adequate account of respect for persons must make reference to epistemic elements. This being the case not only explains why political liberals were correct to incorporate epistemic elements into their accounts of reasonableness but also why it is a mistake to think that perfectionist liberals themselves cannot present an appealing account of respect for persons. Nussbaum’s challenge merits careful study since it both sheds light on the nature of political liberalism and highlights an important faultline in its structure.