Many people have studied how vague predicates depend on context for their interpretation, but few have studied in detail how a use of a vague predicate affects the context against which other expressions get evaluated. In recent years, however, various dynamic theories of context update have made considerable progress in describing and explaining complex phenomena such as presupposition and anaphora. In this paper I will argue that taking an explicitly dynamic perspective on vagueness can lead to new insights into the nature of vagueness in general and the semantics of gradable adjectives in particular.
In order to develop an explicit theory of what a use of a vague expression does, I propose that expressions containing gradable adjectives make a specific kind of contribution to contextual information. Accepting an utterance of, say, Feynman is tall can simultaneously affect mutual assumptions concerning of Feynman's height and of what counts as tall, i.e., it can operate both at a descriptive and at a metalinguistic level. An extension of the basic analysis predicts that update with a use of a measure phrase or a comparative is guaranteed to result in no sharpening of the relevant vague standard. In addition, the dynamic approach naturally leads to a reasonable account of higher-order vagueness in which modifiers such as clearly come out as vagueness quantifiers. A second extension of the basic analysis leads to the first detailed semantics for infinitival-taking adjectives. The somewhat surprising conclusion is that when certain adjectives such as stupid occur with an infinitival complement, the resulting construction has no update effect apart from its presuppositions and its effect on vague standards. Empirical support for this claim comes from the otherwise unexplained fact that infinitival uses of such adjectives cannot be embedded beneath a control predicate (*Feynman wanted to be [stupid to dance like that]). In each case, the update effect of all of these expression types follows directly from stating their truth conditions in a dynamic framework.