Counterfactual confusion
I'm currently writing a chapter on modal realism. I don't like this topic because it always confuses me. Here is one such confusion.
In some world w, pretty much resembling our world, there are two individuals A and B. Let 'A-in-w' be an extremely rich descriptions of A that implies every qualitative truth about w, similarly for 'B-in-w' and B. Now the following two sentences might both be true:
1) If I were A-in-w, I would do X.
2) If I were B-in-w, I wouldn't do X.
Note that, somewhat oddly, (1) implies that A really does X (and (2) that B doesn't), because 'A-in-w' includes everything about A, so if A doesn't do X, then (1) would imply
1*) If I were A-in-w and wouldn't do X, I would do X.
which can't be true, I think. So obviously, some world w_1 where I am A-in-w and do X is closer to actuality than any world where I am A-in-w and don't do X, because there is no such world. Likewise, by (2), some world w_2 where I am B-in-w and don't do X is closer to actuality than any world where I am B-in-w and do X. What's the difference between w_1 and w_2? Any world in which A-in-w is instantiated is a qualitative duplicate of w, as is any world in which B-in-w is instantiated. So w_1 and w_2 are qualitative duplicates of w, and therefore of each other. Hence whatever my counterparts in w_1 do, my counterparts in w_2 do as well -- on any counterpart relation whatsoever. Doesn't this contradict the truth of (1) and (2)? Maybe not, because by saying "if I were A-in-w", I determine that the relevant counterpart relation is one in which A, but not B, is one of my counterparts?