[Asmodeus]

(2) Is most certainly true.

If A == B, then B just is A, we're saying A == A. A possible world where B != A is a world where A != A. You seem to believe that A != B even in our world.

(1) is the essence of the physicalist claim. You can certainly declare it bullshit if you want...

The leap in in (3). While brains and mental states as we know them must be identical, according to physicalists, other worlds may do brain-like and mental-state-like things not as we know them.

For instance, we may have misunderstood our own world.

Oddly, (4) gets back on track. If zombies can be proven to be possible (which conceivability does not do) then physicalism is false. (Although, this generally implies epiphenomenon, which also implies causality is false, which puts consciousness outside of logic {P -> Q} let alone physics.)

[gjm11]

Whether 2 is true depends on how you understand "identical". For sure, if you mean something like "synonymous", then probably "identical" things are the same in all possible worlds. But if you take it broadly enough that, e.g., "consciousness is identical with something that happens in the brain" isn't false by definition then I don't see how your argument works.

I only think 1 is bullshit if you use something like the "synonymous" definition. (Can we agree that it's crazy to say that physicalism requires believing that "consciousness" just means some particular set of brain processes?)

I think your comment about 3 basically amounts to agreeing with me that physicalism doesn't say that mental states and brain states are "identical" in any sense that makes the rest of the zombie argument work.

I agree, of course, that if 1-3 are correct then "zombies are possible" implies "physicalism are wrong".

Epiphenomenalism doesn't imply that causality is false. And if consciousness is "outside of logic" then I say: so much the worse for the notion of consciousness. (But I don't see any reason why we should think consciousness is outside of logic, whether zombies are possible or not.)