A conversation last night with Yuri and Andy helped me to get clearer on the argument I was trying to press in my last post. Here's the much more succinct way to make the point. It's an argument against forms of contextualism that put relevant alternatives into the proposition expressed by knowledge attributions.
Suppose I'm in a nonskeptical conversation, talking about Henry, who is standing in front of a barn. I have no reason to suspect any funny business, so I say, sensibly enough:
(K) Henry knows that he is standing in front of a barn.
Here are are three pretty plausible claims:
(1) If there isn't any funny business going on, my utterance of K is true.
(2) If it turns out that (unbeknownst to me) Henry is in fake barn country, (looking at the only real barn) my utterance of K is false.
(3) My sentence (K) expresses the same proposition, whether or not it turns out that Henry is in fake barn country.
If you think all of these things, then you can't think that the proposition I express builds in the relevant alternatives. Either the possibility that <the thing Henry is standing in front of is a fake barn> is relevant, or it's not, but it's his environment, not my context, that makes it relevant.
So if you want a Schaffer-style extra-argument-place approach to knowledge, this provides a reason not to let that argument place be one for a set of relevant alternatives. You might instead be a function from subject's situations to sets of relevant alternatives.
Yesterday I also included a parallel argument relying on pragmatic encroachment sorts of cases. I think it's a good argument too, but this one proceeds on less contentious premises.