Supervaluationism and good reasoning



Published 06-11-2018
Timothy Williamson


This paper is a tribute to Delia Graff Fara. It extends her work on failures of meta-rules (conditional proof, RAA, contraposition, disjunction elimination) for validity as truth-preservation under a supervaluationist identification of truth with supertruth. She showed that such failures occur even in languages without special vagueness-related operators, for standards of deductive reasoning as materially rather than purely logically good, depending on a context-dependent background. This paper extends her argument to: quantifier meta-rules like existential elimination; ambiguity; deliberately vague standard mathematical notation. Supervaluationist attempts to qualify the meta-rules impose unreasonable cognitive demands on reasoning and underestimate her challenge.

How to Cite

Williamson, T. (2018). Supervaluationism and good reasoning. THEORIA. An International Journal for Theory, History and Foundations of Science, 33(3), 521–537.
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Delia Graff Fara, supervaluationism, supertruth, global validity, vagueness, sorites, ambiguity, meta-rule