Abstract
Despite the prominence of doubt in philosophy since Descartes, the published philosophical literature includes no extended treatment of the nature of doubt. In this paper, I summarize the main contributions that have been made to the subject and then develop a commonsense functionalist account of doubt by specifying the functional role of doubt that something is the case. After adding two further wrinkles, I show how the resulting account can be used to address the questions of how doubt is related to belief and whether suspension of judgment can be identified with doubt. Although the account is partisan, it should hold interest for those who favor other positions in the philosophy of mind, since much of the account can be taken on board by those in other camps, and the paper demonstrates how a sufficiently detailed account of doubt can be put to work addressing longstanding questions of interest across philosophical sub-disciplines.