Ishani and I were talking about who various people here in Canberra are, and we noticed that the following conversation seems coherent, and in an environment where the folk are ignorant of Zaphod Beeblebrox, even plausible.

A: Do you know who that guy is?
B: Yeah, that’s Zaphod Beeblebrox.
A: Who’s Zaphod Beeblebrox?
B: I don’t know. I was just told that’s who that guy is.

The puzzle is that B seems to have contradicted herself. It seems that with her first word she said that she knows who that guy is. And with her second sentence, she said that she doesn’t know who Zaphod Beeblebrox is. But she knows that guy is Zaphod Beeblebrox, so presumably she knows who that guy is iff she knows who Zaphod Beeblebrox is. Contradiction. Yet her words sound consistent, even plausible. What has gone wrong?

_Suggestion_: The problem arises because we substitute into a non-extensional context. It is possible to know that guy is at the party without knowing Zaphod Beeblebrox is at the party, and hence possible to know who that guy is without knowing who Zaphod Beeblebrox is.
_Reply_: True, these substitutions are sometimes problematic. But this is a situation where we don’t just have co-referring expressions, but known to be co-referring expressions. And the knowledge of their co-reference is clearly salient to the speaker. So this probably isn’t what is going wrong.

_Suggestion_: The problem arises because ‘that guy’ is a quantificational rather than a referential expression.
_Reply_: That may well be true. If it is, drop all uses of ‘guy’ from the conversation so we have a simple demonstrative rather than a complex demonstrative. The conversation sounds a little more awkward then, but still coherent.

_Suggestion_: ‘Knows’ is context dependent, as Lewis, Cohen and DeRose have been arguing for donkey’s years.
_Reply_: Even if _all_ the other objections to contextualism don’t work, it is hard to see how on any of their theories there was a change of context between A’s first utterance and B’s second utterance.

_Suggestion_: ‘Knows who’ is context dependent, even though ‘knows’ is not, as Boër and Lycan (among others) have suggested.

I think that’s basically right, and really I’m not sure how a non-contextualist can explain this data. The fact that B doesn’t even _seem_ to have contradicted herself, or taken anything back, looks like a very strong argument for this kind of contextualism. (Compare the examples motivating ‘orthodox’ contextualism where there is a strong feeling that when a speaker first asserts, then rejects, that S knows that p after an alleged context shift. There there is a feeling the author is taking something back.) But in a “recently posted paper”:http://www.ling.rochester.edu/~braun/Papers/nowyouknow.pdf David Braun has argued strongly against this kind of contextualism. The crucial argument, to my mind, concerns the following claim. David argues that if contextualism is true, claims like the following should be true, but they sound false.

bq. ‘Zaphod Beeblebrox is that guy’ is an answer to the question ‘Who is Zaphod Beeblebrox’, and B knows that Zaphod Beeblebrox is that guy, and so she knows an answer to the question of who Zaphod Beeblebrox is, but she does not know who Zaphod Beeblebrox is.

(This is a modified version of his (26) from page 23.) I’d like to have more to say here, but there’s not much more that I can say other that in this little story, this claim sounds _true_ not false. If the claim was false (presumably because the last clause was false) then B’s last claim should sound like it is false. But it doesn’t, it sounds true. So I think the possibility of this conversation is a quite compelling argument for contextualism about ‘knows who’.