An assumption or belief that is taken for granted without proof. The argument was based on the presupposition that all participants had prior knowledge of the topic.
A condition or premise that is assumed in advance of an argument or action. The success of the project relies on the presupposition that funding will be secured.
(Linguistics) A background assumption that must be true for an utterance to be meaningful or truth-evaluatable. The sentence "John stopped smoking" carries the presupposition that John used to smoke.