The question of whether epistemic modals contribute to the truth conditions of the sentences they appear in is a matter of active debate in the literature. Fueling this debate is the lack of consensus about the extent to which epistemics can appear in the scope of other operators. This corpus study investigates the distribution of epistemics in naturalistic data. Our results indicate that they do embed, supporting the view that they contribute semantic content. However, their distribution is limited, compared to that of other modals. This limited distribution seems to call for a nuanced account: while epistemics are semantically contentful, they may require special licensing conditions.
Hacquard, V., & Wellwood, A. (2012). Embedding epistemic modals in English: A corpus-based study. Semantics and Pragmatics, 5. https://doi.org/10.3765/sp.5.4