Epistemicism is a position about vagueness in the philosophy of language or metaphysics, according to which there are facts about the boundaries of a vague predicate which we cannot possibly discover. Given a vague predicate, such as 'is thin' or 'is bald', epistemicists hold that there is actually some sharp cut off, dividing cases where a person is actually thin from those in which they are not. Epistemicism gets its name because it holds that there is no semantic indeterminacy present in vague terms, only epistemic uncertainty.
Epistemicism was typically considered an untenable position, since it requires vague terms to possess extremely specific conditions of application. Since the publication of Timothy Williamson's Vagueness, which defended the view, it has been taken seriously by many philosophers working in the area.