Because they lack sharp boundaries of application, vague words like ‘tall’ and ‘adult’ cause logical and semantic problems in philosophy, decision theory, and the law, among other disciplines. Several theories of vagueness have been proposed to resolve these difficulties, but none has been widely accepted. The book contends that previous accounts have made two critical mistakes: they suppose that a semantic (non-epistemic) theory must abandon bivalence, and they overlook the character of ordinary speech using vague words. The book develops a new theory of vagueness — the multiple range theo ... More

Because they lack sharp boundaries of application, vague words like ‘tall’ and ‘adult’ cause logical and semantic problems in philosophy, decision theory, and the law, among other disciplines. Several theories of vagueness have been proposed to resolve these difficulties, but none has been widely accepted. The book contends that previous accounts have made two critical mistakes: they suppose that a semantic (non-epistemic) theory must abandon bivalence, and they overlook the character of ordinary speech using vague words. The book develops a new theory of vagueness — the multiple range theory — that corrects these errors. The new theory begins with the observation that ordinary speakers apply vague words in multiple arbitrarily different but equally competent ways, even when context is held fixed. (e.g., they stop at different places in a sorites series.) This feature of competent use is taken to reflect multiple ranges of application in the semantics of vague words, where a range of application is a range of properties whose instantiations satisfy a given word on one permissible way of applying it; e.g., a range of ‘tall’ is a range of heights, a range of ‘adult’ a range of ages. The fundamental idea is that a vague word applies to a different set of things relative to each of its ranges — even when context is fixed. The fact that the ranges of a vague word are arbitrarily different — there is no reason to favor any particular one — is key to solving the sorites paradox, perhaps the most serious problem arising from vague words. The multiple range theory employs a classical logic and bivalent semantics. It is more intuitive and simpler than other approaches; e.g., it has no need of a definiteness operator, and it eliminates higher-order borderline cases. A principal conclusion of the book is that competent use of vague words cannot be fully rule-governed; at crucial junctures, use is determined by brute psychological mechanism.