Permissible presupposition

When is it proper or acceptable for a speaker to presuppose a proposition in the course of performing a speech act? Taking Stalnaker's common ground model as my background, I argue that this is best framed as a matter of the conversational permissibility of the speaker's presupposition, and that we should not construe this permissibility in terms of the reasonableness of a speaker's presupposition. Instead, I propose that the permissibility of a speaker's presupposition is fixed by what is mutually conversationally salient to all participants, where this can in principle outstrip what any of the participants reasonably regards as mutually salient.