Presupposition

In linguistics and philosophy, a presupposition is an implicit assumption about the world or background belief relating to an utterance whose truth is taken for granted in discourse. Examples of presuppositions include:

• Jane no longer writes fiction.
  • Presupposition: Jane once wrote fiction.
• Have you stopped eating meat?
  • Presupposition: you had once eaten meat.
• Have you talked to Hans?
  • Presupposition: Hans exists.

A presupposition is information that is linguistically presented as being mutually known or assumed by the speaker and addressee. This may be required for the utterance to be considered appropriate in context, but it is not uncommon for new information to be encoded in presuppositions without disrupting the flow of conversation (see accommodation below).^[1] A presupposition remains mutually known by the speaker and addressee whether the utterance is placed in the form of an assertion, denial, or question, and can be associated with a specific lexical item or grammatical feature (presupposition trigger) in the utterance.

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 presuppose that the subject has done it already one or more times; My wife is pregnant and My wife is not pregnant both presuppose that the subject has a wife. In this respect, presupposition is distinguished from entailment and implicature. For example, The president was assassinated entails that The president is dead, but if the expression is negated, the entailment is not necessarily true.