The commentary records a different later convention, motivated by logical concerns about unrestricted use of the earlier pattern.
«جعل نقيض الثاني أولا وعين الأول ثانيا مع بقاء الصدق ومخالفة الكيف»
Make the complement of the second part the first, keep the original first part as the second, preserve truth, and reverse quality.
Unlike the earlier approach, the original subject is not complemented; rather, the proposition changes from affirmative to negative or vice versa.
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Contraposition: Classical Rules, Validity and the Later Convention
The commentary records a different later convention, motivated by logical concerns about unrestricted use of the earlier pattern.
«جعل نقيض الثاني أولا وعين الأول ثانيا مع بقاء الصدق ومخالفة الكيف»
Make the complement of the second part the first, keep the original first part as the second, preserve truth, and reverse quality.
Unlike the earlier approach, the original subject is not complemented; rather, the proposition changes from affirmative to negative or vice versa.