This variation cannot be explained merely by sentences expressing different propositions relative to different contexts, since it is the same proposition whose truth-value varies.

But this is puzzling. It is not puzzling that the sentence “The murderer might have been on campus at midnight” could be true when uttered in the first context but false when uttered in the second context; that fact could be accommodated by any number of contextualist treatments of epistemic modals, which would dissolve the puzzle by saying that the sentence expresses different propositions relative to the two contexts. The puzzle is that the truth of the second sentence seems to imply that the