Modus Tollendo Tollens

Proof Rule
Modus tollendo tollens is a valid argument in types of logic dealing with conditionals $\implies$ and negation $\neg$.

This includes propositional logic and predicate logic, and in particular natural deduction.

Also see

 * Definition:Conditional

The following are related argument forms:
 * Modus Ponendo Ponens
 * Modus Ponendo Tollens
 * Modus Tollendo Ponens

The Rule of Transposition is conceptually similar, and can be derived from the MTT by a simple application of the Rule of Implication.

These are classic fallacies:


 * Affirming the Consequent
 * Denying the Antecedent