Modus tollens es una regla de inferencia lógica que establece que, si una proposición condicional es verdadera y su consecuente es falso, entonces su antecedente debe ser falso. En forma simbólica, si P implica Q y Q es falso, entonces P es falso.
In propositional logic, modus tollens 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 contrapositive. The inference rule modus tollens asserts that the inference from P implies Q to the negation of Q implies the negation of P is valid.