Category:Modus Tollendo Tollens

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This category contains pages concerning Modus Tollendo Tollens:

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.

Proof Rule

If we can conclude $\phi \implies \psi$, and we can also conclude $\neg \psi$, then we may infer $\neg \phi$.