Prior research suggested the possibility of establishing systematic linkages between some intrinsic features of a presupposition and textual and pragmatic functions that it can carry out with greater probability. This study aims, firstly, to provide an organic view of semantics of presupposition triggers, thanks to a lexical database comprising 19,500 entries. Secondly, the database was used to investigate a corpus of chat conversations including about 200,000 tokens. The results show that triggers occur mainly as non-informative, maintaining an information already known by all participants of the communication; but, depending on their different features, some of them are systematically associated to a function of anaphora and textual cohesion; others to strengthen social conventions and stereotypes. The informative function, although in a minority proportion, is quantitatively significant only in correspondence to a single class of presupposition triggers.