Counterpart theory

The other day I was trying to explain to another philosopher what counterpart theory was in terms which didn’t make me sound like a maniac for sympathising with it, and it wasn’t that easy.

I said that according to a counterpart theorist, she could have been a chef because the world could have contained somebody who was very like her, except she was a chef. (I glossed over technicalities about multiple counterparts and multiple good candidates.) This contrasts with a transworld identity theorist, who says that she could have been a chef because the world could have had her in it being a chef. Similarity is vague and context dependent and identity isn’t, so counterpart theory makes de re modal predication vague and context dependent, and transworld identity theory doesn’t.

I think this is more or less right, but there’s a problem with it. In my explanation of counterpart theory I talked about how the world could have been, and taken at face value that’s a de re modal predication of the world. Now, some people don’t think the world exists, like compositional nihilists, and for them I suppose there’s a difference between a de dicto modal statement and a de re modal predication of the world. Either way you’re having to talk about ways things could have been. If we give a counterpart-theoretic gloss of how I could have been, why don’t we give the same sort of gloss of the way things in general could have been? And if we take ways the things in general could have been as primitive, why not do the same with ways I could have been?

Well, if you’re a modal reductionist you’ve got an answer to this. David Lewis had a bunch of spatiotemporally connected mereological sums representing ways things could have been. Yagisawa had the same things as Lewis but let you cut them up however you like, pretty much making the accessibility relation a counterpart relation. Ersatzists had abstract possible worlds. Once you’ve got ways things could have been you’re up and running and can give your counterpart-theoretic account of who could have been a chef. This keeps the reductive isthmus small, just like Mark Schroeder tells us to.

But what about me? I don’t want to sound like a maniac and I don’t see how ersatz worlds could bear much explanatory weight, so I’ve got nothing to reduce ways things could have been to. I need to take them as primitive, and that means I can’t be a counterpart theorist all the way down.

Perhaps this isn’t so bad. It’s pretty much what Ted Sider does in ‘the ersatz pluriverse’, taking overall possibilities as primitive and doing the rest with counterparts. What intrigues me is whether we’ve any reason to think, after letting in primitive possibilities and necessities for the world, that there aren’t primitive possibilities and necessities for me as well. I guess what I’m pushing is a kind of essentialism: there are some context-independent facts about possibility given by the essences of things, and the rest is counterparts. It’s inspired by a footnote to Naming and Necessity, though I suppose Kripke would be upset if he knew.