Abstract
This paper presents some difficulties for Timothy Williamson's epistemicist view of vagueness and for an argument he gives in its defense. First, I claim that the argument, which uses the notion of an "omniscient speaker", is question-begging. Next, I argue that some presumably true scientific hypotheses, which postulate certain relations between everyday vague predicates and scientific predicates, make the central theses of epistemicism highly implausible. Finally, I show that the "margin for error principles" used by Williamson to explain away the kind of ignorance conjectured by epistemicism lead to new sorites-like arguments with unacceptable conclusions.