Gesture projection and cosuppositions

In dynamic theories of presupposition, a trigger pp' (e.g. it stopped raining) with presupposition p (it rained) and at-issue component p' (it doesn't now rain) comes with a requirement that p should be entailed by the local context of pp'. We argue that some co-speech gestures should be analyzed within a presuppositional framework, but with a twist: an expression p co-occurring with a co-speech gesture G with content g comes with the requirement that the local context of p should guarantee that p entails g; we call such assertion-dependent presuppositions 'cosuppositions'. We show that this analysis can be combined with earlier theories of local contexts to account for complex patterns of gesture projection in quantified and in attitudinal contexts, and we compare our account to two potential alternatives: one based on supervaluations, and one, due to Cornelia Ebert, that treats co-speech gestures as supplements. We argue that the latter is correct, but for 'post-speech' gestures (= gestures that come after the expressions they modify), rather than for co-speech gestures.