Probability and implicatures: A unified account of the scalar effects of disjunction under modals

Sentences involving disjunction under epistemic modal adjectives — such as possible, likely, and certain — give rise to the inference that the disjuncts are epis- temically possible. Inferences of this sort are often classified and treated differently, depending on the force of the embedding modal. Those triggered by possibility modals are singled out as ‘free choice inferences’ (Kratzer & Shimoyama 2002, Klinedinst 2007, Fox 2007, Chierchia 2013, a.o.), while those triggered by stronger modals are called and accounted for in a different way (Sauerland 2004, Fox 2007, Crnic et al. 2015 a.o.). In this paper, we pursue two goals. First, we develop and defend a degree semantics for epistemic modal adjectives, building on much recent work on the topic (Yalcin 2010, Lassiter 2011, 2014, Moss 2015a, Swanson 2015, a.o.). Second, we show that this semantics, in combination with the assumption that scalar implicatures can arise in embedded position (Fox 2007, Chierchia et al. 2012 a.o.), can predict all the inferences triggered by disjunction under modals, including free choice ones, via a uniform mechanism. We conclude by outlining how the proposal can be extended to epistemic modal items in other syntactic categories, and to modals of different flavor.