Notion of validity for the bilateral classical logic

This paper explores proof-theoretic semantics, a formal approach to inferential semantics. It derives sentence meaning from formalized proofs, building upon Gentzen and Prawitz's work. The study addresses challenges in understanding how proofs contribute to sentence meaning. In this setting, classical logic poses "Dummett's challenge" due to its mismatch with the proof-theoretic framework designed for intuitionist logic. For example, in Rumfitt's bilateral classical logic (BCL), the justification of coordination rules, notably RAA, is contentious. This paper employs the notion of validity, introduced by Prawitz, to provide a comprehensive justification for BCL, defining valid arguments and demonstrating its soundness. It resolves the circularity associated with RAA using fixed-point construction. Notably, this approach relies on impredicative comprehension but without on the excluded middle principle, suggesting that bivalence may not be essential for justifying classical logic.