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

Paper Summary

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-modal 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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