First C. presents the paradigm cases of presupposition, i.e. the cases that were adduced in the early discussion of the concept. After introducing later examples, he remarks that most of them do not fit the paradigm. The following dilemma arises: do we have to hold a 'family resemblance view' of presupposition which includes all the non-paradigmatic cases but which makes the concept so vague as to make it useless in logico-linguistic theory, or do we have to hold an 'austere view' which bans all the non-paradigmatic cases? C. argues that one can take up all the examples if one approaches presupposition from the theory of speech acts: presuppositions are some of the necessary conditions for the performance of speech acts.