Vagueness and semantic indiscriminability

I argue, pace Timothy Williamson, that one cannot provide an adequate account of what it is for a case to be borderline by appealing to facts about our inability to discriminate our actual situation from nearby counterfactual situations in which our language use differs in subtle ways. I consider the two most natural ways of using such resources to provide an account of what it is for a case to be borderline and argue that both face crippling defects. I argue that the problems faced by these two accounts point to more general reasons to be skeptical of the claim that facts about semantic indiscriminability provide sufficient resources for an analysis of what it is for a case to be borderline.