Vague Identity and Fuzzy Logic
Copeland (B. Jack)
Source: Journal of Philosophy 94.10, Oct. 1997, pp. 514-534
Paper - Abstract

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Philosophers Index Abstract

    Fuzzy logic extends deductive methods to situations in which the information available may be only partly or approximately true. Fuzzy logic has often been championed as a logic of vague terms, and it does indeed provide an intuitive analysis of what goes wrong in Sorites1 reasoning. Here a fuzzy semantics is given for a language containing the quasi-modal2 operators 'determinately' and 'indeterminately'. The semantics is sensitive to higher-order vagueness. For example, the semantics distinguishes between Herbert's being a clear border-line case of a bald man and his being a borderline border-line case of a bald man. I show that a famous reductio ad absurdum of the statement 'indeterminately (a=b)', due to Gareth Evans, is not valid when the background logic is fuzzy logic. Moreover, an improved form of Evans's reductio due to Harold Noonan is also not valid.

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