The chapter on contradiction established that a proposition and its contradictory necessarily differ in truth value. Reductio applies that principle in an inferential process.
The earlier chapter identified the relation between two propositions. Reductio goes further: it assumes the contradictory, derives an impossibility, rejects the contradictory, and establishes the desired proposition.
The earlier rules governing contradictories of quantified propositions are therefore essential here.
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Qiyās al-Khalf: Compound Reductio, Impossibility and Proof of the Claim
The chapter on contradiction established that a proposition and its contradictory necessarily differ in truth value. Reductio applies that principle in an inferential process.
The earlier chapter identified the relation between two propositions. Reductio goes further: it assumes the contradictory, derives an impossibility, rejects the contradictory, and establishes the desired proposition.
The earlier rules governing contradictories of quantified propositions are therefore essential here.