more from E.J. Lemmon

### Single Idea 9521

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

Full Idea

'Modus tollendo ponens' (MTP) says that if a disjunction holds and also the negation of one of its disjuncts, then the other disjunct holds. Thus ¬P, P ∨ Q |- Q may be introduced as a theorem.

Gist of Idea

'Modus tollendo ponens' (MTP) 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.