Presupposition

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In linguistics, a presupposition is background belief, relating to an utterance, that:

must be mutually known or assumed by the speaker and addressee for the utterance to be considered appropriate in context
Will generally remain a necessary assumption 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.

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.

Negation of a sentence containing a presupposition

If presuppositions of a sentence are not consistent with the actual state of affairs, then one of two approaches can be taken. Given the sentences My wife is pregnant and My wife is not pregnant when one has no wife, then either:

Both the sentence and its negation are false; or
Strawsons approach: Both "my wife is pregnant" and "my wife is not pregnant" use a wrong presupposition (that there exists an object which can be described with the noun phrase my wife) and therefore can not be assigned truth values.

Russell tries to solve this dilemma with two interpretations of the negated sentence:

"There exists exactly one person, who is my wife and who is not pregnant"
"There does not exist exactly one person, who is my wife and who is pregnant."

For the first phrase, Russell would claim that it is false, whereas the second would be true according to him.

Other uses of the term

Critical discourse analysis identifies the ideological function of presuppositions, particularly in the concept of synthetic personalisation.

In epistemology, presuppositions relate to a belief system and are required for it to make sense. Presuppositions form our worldview. The first presupposition we all make is either "there is a god" or "there is no god." From this point, every circumstance and fact we analyze will be categorized to prove one or the other point. A Christian presupposes that there will be life after death. For this reason, he tempers his actions more toward charity and obedience to God.

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