 In general, an identity claim is appropriate when one of the parties to a conversation is (partially) ignorant about which object is picked out by a name like ‘Lloyd’. For an externalist like Stalnaker, this is a case of semantic ignorance. If O’Leary doesn’t know that ‘Lloyd’ is co-referential with ‘I.L. Humberstone’, then he does not fully understand the semantic rules governing these names: i.e., that both names are associated with a constant function from any possible world to a specific individual. But O’Leary isn’t utterly incompetent with the meaning of these terms: he implicitly understands both names as rigid designators, and he has some substantive understanding of the object each name picks out. For instance, he may understand that ‘Lloyd’ refers to the person to whom he’s just been introduced and that ‘I.L. Humberstone’ refers to the author of ‘Direction of Fit’. O’Leary’s semantic deficiency—his failure to fully understand the meaning of these names in a contextually appropriate way—is grounded in his ignorance of the ordinary empirical fact that the man to whom he has been introduced is the author of ‘Direction of Fit’.