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In the branch of linguistics known as pragmatics, a presupposition (or ps) 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 must be mutually known or assumed by the speaker and addressee for the utterance to be considered appropriate in context. It 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. 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. ==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 # Strawson's approach: Both "my wife is pregnant" and "my wife is not pregnant" use a wrong presupposition (i.e. that there exists a referent which can be described with the noun phrase ''my wife'') and therefore can not be assigned truth values. Bertrand 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「presupposition」の詳細全文を読む スポンサード リンク
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