Single Idea 9058

[catalogued under 7. Existence / D. Theories of Reality / 9. Vagueness / f. Supervaluation for vagueness]

Full Idea

Supervaluationist logic (now with a 'definite' operator D) fails to preserve certain classical principles about consequence and rules of inference. For example, reduction ad absurdum, contraposition, the deduction theorem and argument by cases.

Gist of Idea

Some of the principles of classical logic still fail with supervaluationism


R Keefe / P Smith (Intro: Theories of Vagueness [1997], 3)

Book Reference

'Vagueness: a Reader', ed/tr. Keefe,R /Smith,P [MIT 1999], p.30

A Reaction

The aim of supervaluationism was to try to preserve some classical logic, especially the law of excluded middle, in the face of problems of vagueness. More drastic views, like treating vagueness as irrelevant to logic, or the epistemic view, do better.