The presupposition of an utterance concerns the part of encyclopaedic knowledge or the piece of information that the signer assumes in order for the utterance to be meaningful within a specific context. In the example below, the utterance presupposes that Gianni used to smoke before but he stopped doing it.
gianni smoke stop
‘Gianni stopped smoking.’
Similarly to conventional implicatures, presuppositions are triggered by specific lexical meanings. The main distinction between these two pragmatic phenomena is the fact that in presuppositions the additional meaning is relevant for evaluating the truth conditions of the utterance. It means that, in order to consider the descriptive meaning true (‘Gianni stopped smoking’), the interlocutor needs to assume that the presupposed meaning is true (‘Gianni used to smoke’).