• 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.