What ought one to do, epistemically speaking, when faced with a disagreement? Faced with this question, one naturally hopes for an answer that is principled, general, and intuitively satisfying. We want to argue that this is a vain hope. Our claim is that a satisfying answer will prove elusive because of non-transparency: that there is no condition such that we are always in a position to know whether it obtains. When we take seriously that there is nothing, including our own minds, to which we have assured access, the familiar project of formulating epistemic norms is destabilized. In
this paper, we will show how this plays out in the special case of disagreement. But we believe that a larger lesson can ultimately be extracted from our discussion: namely, that non-transparency threatens our hope for fully satisfying epistemic norms in general.