Presupposition

There are various senses in which one statement may be said to ‘presuppose’ another, senses which are in permanent danger of being confused. Prominent among them are Strawsonian presupposition, a relation which obtains between statements when the falsity of one deprives the other of truth-value (for example, ‘There was such a person as Kepler’ is a Strawsonian presupposition of ‘Kepler died in misery’); semantic presupposition, which obtains between a statement and a particular use of a sentence type, when the falsity of the statement means that that use will not after all constitute the making of a statement (for example, ‘The name “Kepler” has a bearer’ is a semantic presupposition of ‘Kepler died in misery’); and pragmatic presupposition, a broader notion exemplified by the legitimate presumption that accepting or denying the statement ‘Fred knows that the earth moves’ means accepting ‘The earth moves’.