Modal Realism

(1) If David Lewis were alive, he would not like that I am invoking his name here.

David Lewis was a philosopher who investigated modal logic, and concluded that all this talk of possible worlds — which goes all the way back to Leibniz — is a very handy way to get around a lot of the philosophical problems raised by modal if-then statements.  In fact, it’s as handy as a lot of mathematical concepts that we routinely use to solve problems, and regard as “existing” as abstract entities.  If, he suggested (and this is a brief abbreviation of his argument), we can get use out of abstract mathematical entities and regard them as existing, in some sense, then it makes sense to treat modal possible worlds as existing.

This idea is called modal realism, and it argues this:

We make sense of (1) by imagining a world in which David Lewis were still alive.  He’s not alive in this “actual” world, but he is alive — really, truly alive — in some other world about which we can make statements like (1).  We could just say that (1) is meaningless (which isn’t satisfying).  Or we could say that (1) requires us to construct some imaginary possible world.  But that’s not quite what we’re doing.  We’re not constructing such a world, he says: we’re making statements about such a world that already exists.

We exist in an actual world, but that “actual” is indexical.  It’s positioning ourselves within a framework of possible worlds.

For Lewis, and other adherents to this position, the possible worlds are causally separate.  You can’t travel between them, or communicate through them.  There’s a me who is president somewhere in the infinitude of possible worlds, but we’ll never talk or meet or anything.  Nothing I do affects him, and nothing he does affects me.  (And he is, of course, me.  And that raises whole other issues, many of them sticky.)

Don’t confuse this with the multiple universe hypothesis of quantum physics.  Completely unrelated.

Why does this matter for magic?  Because I think the causal separation of modal worlds is not entirely accurate, and I’ll explain why in my next post, when we look at configuration space and the flexibility of deictics.


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