June 2006 Axiomatizing Kripke’s Theory of Truth
Volker Halbach, Leon Horsten
J. Symbolic Logic 71(2): 677-712 (June 2006). DOI: 10.2178/jsl/1146620166


We investigate axiomatizations of Kripke’s theory of truth based on the Strong Kleene evaluation scheme for treating sentences lacking a truth value. Feferman’s axiomatization KF formulated in classical logic is an indirect approach, because it is not sound with respect to Kripke’s semantics in the straightforward sense; only the sentences that can be proved to be true in KF are valid in Kripke’s partial models. Reinhardt proposed to focus just on the sentences that can be proved to be true in KF and conjectured that the detour through classical logic in KF is dispensable. We refute Reinhardt’s Conjecture, and provide a direct axiomatization PKF of Kripke’s theory in partial logic. We argue that any natural axiomatization of Kripke’s theory in Strong Kleene logic has the same proof-theoretic strength as PKF, namely the strength of the system RAω ramified analysis or a system of Tarskian ramified truth up to ωω. Thus any such axiomatization is much weaker than Feferman’s axiomatization KF in classical logic, which is equivalent to the system RA<ε₀ of ramified analysis up to ε₀.


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Volker Halbach. Leon Horsten. "Axiomatizing Kripke’s Theory of Truth." J. Symbolic Logic 71 (2) 677 - 712, June 2006. https://doi.org/10.2178/jsl/1146620166


Published: June 2006
First available in Project Euclid: 2 May 2006

zbMATH: 1101.03005
MathSciNet: MR2225901
Digital Object Identifier: 10.2178/jsl/1146620166

Keywords: axiomatic theories of truth , Kripke-Feferman theory , liar paradox , partial logic , reflective closure , Strong Kleene scheme , Truth

Rights: Copyright © 2006 Association for Symbolic Logic


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Vol.71 • No. 2 • June 2006
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