The Importance of Presupposition

The title of this paper may seem presumptuous. But I have chosen it anyway, as a signal of what I see as the central insight that recent studies of presuppo-sition in natural language have given us. Presuppositions are not what early discussions suggested and later ones have, I feel, still done too little to explicitly refute: obstacles to logical transparence, logical simplicity or well-deenedness of meaning, and thus a thing that languages would have been better oo without. On the contrary, presuppositions are valuable tools which language uses to guide the recipient of an utterance, discourse or text towards its intended meaning. In fact, given what we are beginning to understand about the ways in which presuppositions arise and the purposes they serve, it is hard to imagine how a natural language could exist without them. This paper is part of a larger enterprise and the rst of a series. So it would seem to be the right place for a general overview of the theory that has been the target of this enterprise and to say enough about it to give a clear idea of how it works, and how it diiers from other presupposition theories. Unfortunately, this would have required a paper well in excess of what is acceptable in a collection like the present one. So I have had to temper my ambitions and to select some parts of the overall account for special focus, while leaving out a good many others. After some hesitation what to retain of earlier, much bulkier drafts I decided to focus on two aspects of presupposition theory which seem to me to have received comparatively little attention in the literature so far. The rst is one that one might describe as`presuppositional multiplicity': Natural language sentences often give rise not just to one presupposition but to several presuppositions at once. It turns out that combinations of presuppositions triggered within one and the same sentence pose problems that go beyond what we see when focusing on individual presuppositions, as much of the existing