modus ponendo tollens

Borrowed from Latin modus pōnendō tollens (roughly, “mode where affirming infirms”).

modus ponendo tollens (uncountable)

1. (philosophy, logic) A valid form of argument in which the antecedent of a conditional proposition is affirmed, thereby entailing the infirmation of the consequent. Modus ponendo tollens has the form:

   1. If P, then non-Q.

   2. P.

   3. Therefore, non-Q.

• inference rule
• See also Thesaurus:argument form

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