In pragmatics, a presupposition is an assumption about the world whose truth is taken for granted in discourse. Examples of presuppositions include:
- Do you want to do it again?
- Presupposition: You have done it already, at least once.
- My wife is pregnant.
- Presupposition: The speaker has a wife.
Crucially, negation of an expression does not change its presuppositions: I want to do it again and I don't want to do it again both mean that the subject has done it already one or more times; My wife is pregnant and My wife is not pregnant both mean that the subject has a wife. In this respect, presupposition is distinguished from entailment and implication. For example, The president was assassinated entails that The president is dead, but if the expression is negated, the entailment is not necessarily true.
If presuppositions of a sentence do not comply with the actual state of affairs, then both the sentence and its negation are false.
Critical discourse analysis identifies the idoelogical function of presuppositions, particularly in the concept of synthetic personalisation.