This paper motivates and develops a novel semantics for several epistemic expressions, including possibility and necessity modals and indicative conditionals. The semantics I defend constitutes an alternative to standard truth conditional theories, as it assigns sets of probability measures rather than sets of worlds as sentential semantic values. I argue that what my theory lacks in conservatism, it makes up for in strength — namely, the theory accounts for a host of distinctive and suggestive linguistic data collected and explored in this paper. http://dx.doi.org/10.3765/sp.8.5 BibTeX info