Defeasibility (linguistics)

In the linguistic field of pragmatics, an inference is said to be defeasible or cancellable if it can be made to disappear by the addition of another statement, or an appropriate context. For example, sentence [i] would normally implicate [ii] by scalar implicature:

i: Alice has three children.

ii: Alice has exactly three children.

But the implicature can be cancelled by the modification in [ib]:

ib: Alice has three children, and possibly more.

Whereas conversational implicatures and presuppositions may be cancelled, an entailment may not be. For example, [i] entails the proposition "Alice has at least three children", and this cannot be cancelled with a modification like:

ic: Alice has three children, and possibly less.