Existence Presuppositions and Background Knowledge

When a definite noun phrase fails to refer, the statement containing it is often felt to lack a truth value, as in The king of France is bald. In other examples, however, the statement seems intuitively false, and not truth-valueless: consider the case of a speaker who points at an obviously empty chair and says The king of France is sitting in that chair. The difference appears to depend on the pragmatics of verification; we know the sentence is false because the chair is empty-the question of the existence of the king of France need not even come up. A semantics is sketched for assigning truth values to sentences relative to information states. A sentence containing a definite NP may be evaluated as false relative to a given information state rather than simply truth-valueless if, after removing the information that the NP fails to refer, the resulting information state still cannot be consistently extended to one making the sentence true. On this assumption, existing proposals for the semantics of negation in information-state semantics turn out to correspond to internal and external negation, respectively.