Thesis: Ph. D., Massachusetts Institute of Technology, Department of Linguistics and Philosophy, 2016."September 2016." Cataloged from PDF version of thesis.Includes bibliographical references (pages 119-134).I argue that knowledge and rational belief are subject to stability conditions. A belief that amounts to knowledge couldn't easily have been lost due to the impact of misleading evidence. A belief that is rational couldn't easily have been withdrawn upon reflection on its epistemic credentials. In Chapter 1, I support a picture of epistemic rationality on which a belief, in order to be rational, must be stable under reflection, i.e., it must be capable of surviving reflective scrutiny. To make room for this condition, I defend the poss...