Presuppositions, provisos, and probability

Theories of presupposition in the tradition associated with Karttunen, Stalnaker and Heim relate presupposition satisfaction to the content of conversational participants’ epistemic states, usually modeled as sets of worlds. However, converging evidence from recent work on modality and from other areas of cognitive science suggests that epistemic states are better thought of as having the richer structure of probability distributions. I describe an account of semantic and pragmatic presupposition which combines core ideas from dynamic semantic treatments with a probabilistic model of information states and their dynamics in conversation, and argue that it predicts the core data of the proviso problem (Geurts 1996) without invoking ad hoc mechanisms as conditional strengthening accounts typically do. The frequently cited intuition that (ir)relevance is crucial follows without stipulation, and I present new cases which suggest that irrelevance is too weak to predict all cases of unconditional presuppositions, problematizing strengthening accounts which rely on it. The proposed theory is able to account for this new data and also for semi-conditional presuppositions, a sticking point for previous theories of presupposition projection. I argue that this perspective also gives us a reasonable line on several related issues, including the divergence between presupposed conditionals and conditional presuppositions, instances of the proviso problem in counterfactuals, and the contextual variation in the difficulty of accommodation.