Modus Tollens is a rule of inference used in propositional logic, used to break up a conditional statement. It goes like this:

If P, Then Q.
¬Q (Not Q)
Therefore, ¬P.

If Socrates is a god, then he is immortal.
It is not the case that Socrates is immortal.
Therefore Socrates is not a god.

Modus Tollens is Latin for "the mode that denies", as the ¬Q denies the conditional. It is often abbreviated as MT. Don't confuse it with Denying the Antecedent, that is a fallacy, and it is just wrong.


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