• Korean Journal of Logic
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• v.18 no.3
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• pp.307-335
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• 2015

An important component in Prawitz's and Dummett's proof-theoretic accounts of validity is the condition for validity of open arguments. According to their accounts, roughly, an open argument is valid if there is an effective method for transforming valid arguments for its premises into a valid argument for its conclusion. Although their conditions look similar to the proof condition for implication in the BHK explanation, their conditions differ from the BHK account in an important respect. If the premises of an open argument are undecidable in an appropriate sense, then that argument is trivially valid according to Prawitz's and Dummett's definitions. I call this 'the triviality problem'. After a brief exposition of their accounts of proof-theoretic validity, I discuss triviality problems raised by undecidable atomic sentences and by Godel sentence. On this basis, I suggest an emendation of Prawitz's definition of validity of argument.

• Korean Journal of Logic
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• v.6 no.2
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• pp.1-22
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• 2003

타당한 논증과 논리적 귀결에 대한 프라위츠와 더밋의 증명 이론적 정의는 그 적절성을 위해 이른바 "근본 가정"과 "도입규칙들은 자체적으로 정당한 규칙들이다"는 두 논제들을 전제하고 있다. 이 글에서는 어떤 규칙들 특히 도입규칙들이 자체적으로 정당하다는 두 번째 논제가 어떻게 이해될 수 있는지 살펴보고, 이 논제를 보다 분명히 드러내 보이려는 한 신도를 비판적으로 검토할 것이다. 그런 과정 중에 이 두 논제의 관계도 보다 분명히 드러내 보일 것이다.

• Korean Journal of Logic
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• v.16 no.3
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• pp.407-436
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• 2013

I examine the notion of truth in the intuitionistic type theory and provide a better explanation of the objective intuitionistic conception of mathematical truth than that of Dag Prawitz. After a brief explanation of the distinction among proposition, type and judgement in comparison with Frege's theory of judgement, I examine the judgements of the form 'A true' in the intuitionistic type theory and explain how the determinacy of the existence of proofs can be understood intuitionistically. I also examine how the existential judgements of the form 'Pf(A) exists' should be understood. In particular, I diagnose the reason why such existential judgements do not have propositional contents. I criticize an understanding of the existential judgements as elliptical judgements. I argue that, at least in two respects, the notion of truth explained in this paper is a more advanced version of the objective intuitionistic conception of mathematical truth than that provided by Prawitz. I briefly consider a subjectivist's objection to the conception of truth explained in this paper and provide an answer to it.