Modus tollendo ponens

Modus tollendo ponens (literally: mode which, by denying, affirms) is a valid, simple argument form:


 * P or Q
 * Not P
 * Therefore, Q

An English language example:


 * Either Jim's in the library, or he's in the pub.
 * But he's not in the library.
 * So he must be in the pub.

Unlike modus ponendo ponens and modus tollendo tollens, with which it should not be confused, MTP is often not made an explicit rule or axiom of logical systems, as the above arguments can be proven with a (slightly devious) combination of reductio ad absurdum and disjunction elimination.

MTP should also not be confused with modus ponendo tollens.

External link

 * Proof of MTP