Definition of modus tollens in English:

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modus tollens

Pronunciation: /ˌmōdəs ˈtälenz/


1The rule of logic stating that if a conditional statement (“if p then q”) is accepted, and the consequent does not hold (not-q), then the negation of the antecedent (not-p) can be inferred.
Example sentences
  • Some philosophers have defended the view that animals are not sentient and attempted to use a component conditional for modus tollens.
  • First, although modus ponens has a probabilistic analog, modus tollens does not - the fact that a hypothesis says that an observation is very improbable does not entail that the hypothesis is improbable.
  • From a conditional statement, one can construct two types of valid inference: modus ponens and modus tollens.
1.1An argument using modus tollens.
Example sentences
  • One use of modus tollens is the reductio ad absurdum argument, i.e. showing that a premise is false by demonstrating that it implies an absurd conclusion.
  • This argument has the modus tollens form, and hence is valid - if its premisses are true, then its conclusion must be true as well.
  • Once this is shown, the consequences invite a modus tollens; the mere vulnerability of proposed reductions is hardly enough to support the view with such exotic consequences.


Latin, literally 'mood that denies'.

For editors and proofreaders

Syllabification: mo·dus tol·lens

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