Abstract

This dissertation explores several accounts of the intuitions speakers have concerning the truth values of utterances of sentences containing vague nouns and adjectives. While some semanticists have attempted to account for these intuitions with multi-valued logics and supervaluation theories of truth, I focus on how utterances of vague sentences affect hearers' beliefs. ;Following a critique of the major semantical accounts of vagueness, I propose a formal theory of how beliefs are revised following utterances of sentences of the form X is A, X is A and B, and X is A and not A, where A and B are vague scalar adjectives. Formally, a hearer's beliefs are represented as a set of weighted sentences, and the information conveyed by a speaker's utterance is represented as a set of weighted conditionals. When a speaker utters a sentence, a function on these sets yields the hearer's revised beliefs. I derive from this theory a criterion for proper assertability: a sentence is properly assertable in a given context if the maximum information loss that could obtain between competent discourse participants is less than some threshold. I argue that this criterion often predicts the truth-value judgements competent speakers make which violate the basic rules of logic. I extend these theories to utterances of sentences containing vague non-scalar nouns. ;In the second half of the dissertation, I propose two semantic accounts of vagueness. One incorporates the assertability criterion into its definition of truth. The other is independent of it. The former accounts for a large set of intuitions concerning the truth values of utterances of vague sentences. The latter accounts for only a subset of those intuitions, leaving the rest to be explained independently by the theory of proper assertability. ;I conclude with brief discussions of the Sorites Paradox and the experimental data obtained by Tversky and Kahneman which purport to demonstrate people's poor intuitions concerning the probabilities of conjunctions.