Under the earlier convention, the categorical outcomes are:
Universal affirmative → universal affirmative.
Particular affirmative → no generally valid contrapositive.
Universal negative → particular negative, assuming subject existence.
Particular negative → particular negative.
The table is not merely mnemonic. Complement both terms, exchange them, then test whether the required quantity and quality preserve truth.
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Contraposition: Classical Rules, Validity and the Later Convention
Under the earlier convention, the categorical outcomes are:
Universal affirmative → universal affirmative.
Particular affirmative → no generally valid contrapositive.
Universal negative → particular negative, assuming subject existence.
Particular negative → particular negative.
The table is not merely mnemonic. Complement both terms, exchange them, then test whether the required quantity and quality preserve truth.