In chapter 5,1 argued against linguistic accounts of vagueness on the grounds that if it is true that we cannot know whether Harry is bald, then this is not because of the way the English sentence ‘Harry is bald' happens to be used. Whether a belief that Harry is bald constitutes knowledge or not, I suggested, is just not sensitive to facts about your linguistic environment.

Whether or not vagueness is linguistic, there is a quite general puzzle as to how we acquire vague beliefs at all, and as to what role, if any, language plays in the acquisition of these beliefs.

Could a mentalese sentence have this kind of role without the thinker standing in some kind of important relation to a public language? If vagueness is a linguistic phenomenon, it is hard to see how this story could work unless the thinker did stand in such a relation. According to the analysis of vagueness in terms of semantic indecision, for example, the feature that distinguishes sentences like ‘Harry is bald' from sentences like ‘Harry has at most n hairs' is to be spelled out in terms of the different ways in which these sentences are used to coordinate beliefs between members of a linguistic community. For this talk of coordination to even make much sense, we must be talking about a community that contains at least two members.^[78] Thus whether one has vague beliefs at all, according to this proposal, is dependent on one speaking a public language. Indeed this kind upshot is already partially anticipated by conclusions of Burge [21], that purportedly show that whether one has beliefs involving arthritis and other ‘deferential' concepts can be sensitive to your linguistic environment. While these arguments have enjoyed a moderate amount of acceptance among philosophers, the present proposal is far more radical and far reaching.

An argument that purports to show that one cannot have vague beliefs unless one speaks a public language would threaten to show that we could have barely any beliefs at all unless we spoke a public language.

There are plenty of other things to say about this proposal. My purpose in this chapter is rather to highlight other mechanisms by which we acquire vague beliefs which the linguistic theorist cannot account for. I shall argue that most of our beliefs do not require any familiarity with a public language; most of our vague beliefs are acquired via our sensory faculties, vision, smell, proprioception, or other non- linguistic faculties such as memory. Sometimes public language sentences express vague propositions and these sentences can be used to communicate vague beliefs. But the class of vague propositions which satisfy the evidential profiles outlined vastly outstrips the class of propositions expressed in any given language and, moreover, the way in which language features in our acquisition of vague beliefs acquired this way is minimal.

In section 6.1, I introduce the idea of one's evidence being ‘inexact' and argue that there are important connections between these cases and cases in which one's evidence consists of vague propositions. More specifically, I argue that updating on vague evidence is a particular instance of a more general account of updating on inexact evidence: Jeffrey updating relative to a partition—in this case relative to a set of ‘precisifications'. This observation leads to a couple of insights into the evidential relation between vague propositions and precise propositions that will form the basis for the account of vagueness I am advancing in this book. One of these, which I will develop in chapter 8, is that one's beliefs in the vague propositions are completely fixed (in a sense to be spelled out) by one's beliefs in the precise. Thus one's beliefs in a particular vague proposition can be uniquely determined by one's beliefs in the precise and a particular evidential relationship to the precise propositions. The way in which credences in a vague proposition depend on credences in the precise propositions will be called the evidential role of the vague proposition. The second insight, which I defend in this chapter, is a Principle of Plenitude: that for any possible evidential role in thought, there is some vague proposition which has that role.

6.1