Bach's Dilemma

(1) If a referring expression functions referringly in some contexts and not in others and that fact is semantically significant, then the expression's semantic contribution to the sentence in which it occurs would have to depend on its sentential context.

(2) But this suggests that its very meaning, which presumably determines its semantic contribution, depends on its sentential context.

(3) The only way to concede that, and this is one horn of the dilemma, would be to abandon the Principle of Compositionality.

(4) The other horn of the dilemma is to accept the dubious implication that referring expressions are systematically ambiguous.

Since the only way to keep (1) is to reject (3) or (4) it seems that we must then reject (1). Bach's claim is that expressions don't refer, rather speaker's refer. So, if it is expressions themselves that refer and they need a context in which to refer from, then it seems that (3) or (4) is true.