||Epistemic modals, like 'must' and 'may', are propositional operators that express various brands of epistemic necessity and possibility. Unlike metaphysical possibility operators, which typically say something about the way the world could have been (given the nature of things), epistemic modals typically say something about the way the world may be (given what is known). The semantics of epistemic modals is elusive. Epistemic modal claims shift their truth values rather easily and much of the debate concerns the source of that shiftiness. Do epistemic modals deserve a truth function semantics? Are they context sensitive like indexicals? Why does their contribution to semantic content change when we embed them under complex sentences like conditionals and conjunctions?