### Single Idea 9522

#### [catalogued under 4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / d. Basic theorems of PL]

Full Idea

'Modus ponendo tollens' (MPT) says that if the negation of a conjunction holds and also one of its conjuncts, then the negation of the other conjunct holds. Thus P, ¬(P ∧ Q) |- ¬Q may be introduced as a theorem.

Gist of Idea

'Modus ponendo tollens' (MPT) says P, ¬(P ∧ Q) |- ¬Q

Source

E.J. Lemmon (Beginning Logic [1965], 2.2)

Book Reference

Lemmon,E.J.: 'Beginning Logic' [Nelson 1979], p.61

A Reaction

Unlike Modus Ponens and Modus Tollens, this is a derived rule.