Modus tollens

In propositional logic, modus tollens (or modus tollendo tollens and also denying the consequent) (Latin for "the way that denies by denying") is a valid argument form and a rule of inference. It is an application of the general truth that if a statement is true, then so is its contra-positive.

The first to explicitly describe the argument form modus tollens were the Stoics.

The inference rule modus tollens validates the inference from ${\displaystyle P}$ implies ${\displaystyle Q}$ and the contradictory of ${\displaystyle Q}$ to the contradictory of ${\displaystyle P}$.

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