Modus tollens

if X implies Y, and Y isn't true, then neither is X

Modus tollendo tollens (Latin: the way that denies by denying)[1] is a valid, simple argument form in classical logic. It is referred to as denying the consequent. It is closely related to another valid form of argument, modus ponens or affirming the antecedent. Modus tollens is a very common rule of inference, and takes this form:

If P, then Q.
Not Q.
Therefore, not P.[2]

References change

  1. Stone, Jon R. (1996). Latin for the Illiterati: exorcizing the ghosts of a dead language. London, UK: Routledge: 60.
  2. University of North Carolina, Philosophy Department, Logic Glossary Archived 2007-08-30 at the Wayback Machine.