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.

‘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.’

‘Only universal claims are susceptible to the application of modus tollens that underlies falsifiability.’

1.1An argument using modus tollens.

‘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.’

‘So, by modus tollens, I don't know that I have hands.’

‘But when dealing with probabilistic arguments, such as found in the intelligent design approach, modus tollens does not hold anymore.’

Origin

Latin, literally ‘mood that denies’.

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