In ethics, it is commonly supposed that we have both positive duties and negative duties, things we ought to do and things we ought not to do. Given the many parallels between ethics and epistemology, we might suppose that the same is true in epistemology, and that we have both positive epistemic duties and negative epistemic duties. I argue that this is false; that is, that we have negative epistemic duties, but no positive ones. There are things that we ought not to believe, but there is nothing that we ought to believe, on purely epistemic grounds. I also consider why the parallels between ethics and epistemology break down at this particular point, suggesting that it is due to what I call the infinite justificational ‘fecundity’ of perceptual and propositional evidence.