Does _Ought_ Imply _Can_ in Epistemology?

Can epistemology require the impossible? Many philosophers believe the answer is ‘no’; if an epistemological theory generates a requirement that it would be impossible to satisfy, then, no matter how attractive the theory is, it is false. This view seems to depend on the idea that ought implies can in epistemology, at least in some sense. How should we understand this principle? In this paper, I introduce and explore a strong version of an epistemic ought implies can principle whereby an epistemic ought implies a psychological can. I outline a novel way to understand this principle—one which takes it in a contextualist spirit—and argue that it can meet two serious challenges that often lead philosophers to reject similar principles. The challenges are making the notion of ‘psychological ability’ sufficiently clear and avoiding an excessive permissiveness which diminishes the normative force of epistemic requirements. The upshot is that a strong epistemic ought implies can principle is more plausible than many philosophers think.