> (also see all the different logics philosophers use to formalise different kinds of argument involving time/modality/probability - there are a lot, but they aren't very "modular" and can't easily be mixed unless someone has solved that since I last looked into it)

From a logic-as-types perspective, modalities turn out to be monads. So the problem of "mixing" modalities is quite similar to the problem of composing monads in programming languages.