Modus ponendo tollens (MPT; Latin: 'mode that denies by affirming') is a valid rule of inference for propositional logic. It is closely related to modus ponens and modus tollendo ponens. Modus ponendo tollens (MPT; Latin: 'mode that denies by affirming') is a valid rule of inference for propositional logic. It is closely related to modus ponens and modus tollendo ponens.