THE MODAL BASE PRESUPPOSITION: Natural language expressions that contain a modal component in their meaning, including all English modal auxiliaries and Epistemic Modal Auxiliaries (EMA)s in particular, presuppose a modal base, a function that draws from context a relevant set of propositions which contribute to a premise-semantics for the modal.
Accepting this thesis for EMAs leaves open (at least) the following two questions about the meaning of English EMAs like must and might:
i. What constraints, if any, are there on the character of the premise set for an EMA?
ii. What is the nature of the relationship between premises and conclusion that is required for truth of the EMA statement?
I argue for at least a partial answer to (i), with two hypotheses about the proper constraints on the modal base for an EMA:
EVIDENTIALITY: The modal base for an EMA is evidential and doxastic, not truly epistemic (i.e., weak, not strong).
INDEXICALITY: EMAs, unlike some other types of modals, are indexical: They are anchored to an agent-at-a-time whose doxastic state is currently under discussion in the context of utterance.
These constraints are modeled as presuppositions triggered by the EMA, restrictions on the modal’s domain. The independently motivated indexical anchoring (a) correctly predicts the contextually limited range of candidates for the anchoring agent of such a modal, as attested in the literature, (b) thereby constrains what body of evidence is understood to be relevant (that of the anchor), and (c) in some cases plays a role in explaining the modal’s scope (not discussed here). The account sheds light on several puzzles, including (d) Yalcin’s (2007) version of Moore’s paradox for embedded epistemic modals, and (e) purported arguments for modal relativism (e.g., Egan, Hawthorne & Weatherson 2005).