Two-dimensional semantics and the nesting problem∗

Graeme Forbes (2011) raises some problems for two-dimensional semantic theories. The problems concern nested environments: linguistic environments where sentences are nested under both modal and epistemic operators. Closely related problems involving nested environments have been raised by Scott Soames (2005) and Josh Dever (2007). Soames (forthcoming) goes so far as to say that nested environments pose the “chief technical problem” for strong two-dimensionalism. We might call the problem of handling nested environments within two-dimensional semantics the nesting problem. We concentrate especially on Forbes’s version of the nesting problem here, with some attention to Dever’s version as well (Chalmers 2011a discusses Soames). Forbes concentrates especially on sentences in which a factive epistemic operator, such as ‘Someone establishes that’ or ‘It is a priori that’ is embedded within a further modal or epistemic operator. His key examples are versions of the following: