Thesis (Ph. D. in Philosophy)--Massachusetts Institute of Technology, Dept. of Linguistics and Philosophy, 2012.Cataloged from PDF version of thesis.Includes bibliographical references.Being rational and being moral can be difficult. However, some theories of rationality and morality make living up to these ideals too difficult by imposing requirements which are excessively rigid. In this dissertation, I defend and explore the implications of relaxing some of these requirements. I first consider the implications of thinking that rational agents' doxastic attitudes can be represented by imprecise, rather than precise probabilities. In defending this position, I develop a distinction between an idealized, and less idealized notion of rational...