This chapter develops and defends an account of reason: to reason is to scrutinize one’s attitudes by consulting the perspectives of other persons. The principal attraction of this account is its ability to vindicate the unique of authority of reason. The chapter argues that this conception entails that reasoning is a robustly social endeavor—that it is, in the first instance, something we do with other people. It is further argued that such social endeavors presuppose mutual respect on the part of those participating in them. The account therefore yields a form of Kantian constructivism: we have an unconditional duty of respect for persons because such a duty is implicit in the very nature of reasoning.