Vagueness and common ground: the problem of sharp contours

This paper offers a criticism of Barker and MacFarlane’s approach to vagueness and communication. In their view, it is not problematic, as far as vagueness is concerned, to specify the content of a vague sentence: it is simply a function that updates the common ground. What is tricky, as far as vagueness is concerned, is to specify the common ground. In this paper, I will argue that their view is committed to attributing unreasonable propositional attitudes to at least one participant of any conversation. I explore a possible solution to this problem that uses MacFarlan’s toolkit and find it wanting. At its core, the discussion in this paper is about how to represent the common ground when we take the phenomenon of vagueness seriously. As such, the problem discussed here comes up in every theory of vague linguistic communication that relies upon a standard notion of common ground.