modus tollendo tollens

Borrowed from Latin modus tollendō tollēns (roughly, “mode where infirming infirms”).

modus tollendo tollens (uncountable)

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

   1. If non-P, then non-Q.

   2. non-P.

   3. Therefore, non-Q.

• inference rule
• See also Thesaurus:argument form

• modus ponendo ponens
• modus ponendo tollens
• modus tollendo ponens