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Having read through the first third of the paper or so, here's some thoughts. I'm not convinced by the fact that showing 'possibility' of zombies is enough to

Having read through the first third of the paper or so, here's some thoughts. I'm not convinced by the fact that showing 'possibility' of zombies is enough to eliminate physicalism. The argument they use is too slippery for me to grasp, but it basically sounds to me something like this: Skeptics think that the laws of physics are sufficient to describe the universe. It suffices to show that magic is possible, and then skepticism is false. This is why opponents of skepticism do not have to point to actual cases of magic being performed; it is enough if such things are possible. Second, along the lines of conceivable -> possible, here's an interesting thought experiment. I can conceive of an immovable object. An object such that when it is inserted into our universe, it can never be moved with respect to some frame of reference. Such an object is much easier to conceive of than a zombie. I can conceive of an irresistable object. This object is such that it moves with constant velocity relative to some frame of reference, and its velocity can never be changed. I find it hard to accept that the possibility of such concepts can be used to show anything useful about the universe. Further on, I found that the best counterexample included was that of Daniel Dennett, who compares the idea of consciousness against the idea of health - to quote the quotation: Supposing that by an act of stipulative imagination you can remove consciousness while leaving all cognitive systems intact — a quite standard but entirely bogus feat of imagination — is like supposing that by an act of stipulative imagination, you can remove health while leaving all bodily functions and powers intact. … Health isn’t that sort of thing, and neither is consciousness (1995, 325). <end quotation> Finally, it's nice that they went out and mentioned all the issues with semantics around the concepts of 'conceivable' and 'possible', because that was the part that feels like it wants to give me a migraine. Last thought: One of the ideas was that whatever it is that distinguishes us from zombies does not exist in a physical sense. But we have devices that can read our thoughts - or at least show that our physical state is changing while we think. My MRI shows brain activity, therefore I am.

gjm11 17y ago
The alleged inference from "zombies are possible" to "physicalism is wrong" isn't quite what you say. It goes more like this. (1) If physicalism is correct, then (e.g.) mental states are identical to physical brain states. (Or something along those lines.) (2) But if A is identical to B, then A = B in all possible worlds; that is, A is necessarily the same as B. (3) Therefore, if physicalism is correct, then in no possible world are there zombies; necessarily, there are no zombies. (4) In other words, if it is possible that there are zombies, then physicalism is wrong. I think this argument is rubbish. Claim 2 seems like obvious bullshit, unless "identical" is given some weird technical meaning that makes claim 1 bullshit instead. Further, with the sense of "possible" that's relevant here it's very far from clear that anyone's shown that zombies are possible. (The SEP page treats this point quite well.) I have used the following parallels before: I can imagine electric current flowing without any charged particles being present, "therefore" electric current is not the same thing as the movement of charged particles; I can imagine my computer continuing to do what it does without its circuitry and what happens therein, "therefore" the processing my computer does is not a mere activity of its circuitry. What twaddle. (See http://www.mccaughan.org.uk/g/log/2007/inconceivable.html http://www.mccaughan.org.uk/g/log/2007/inconceivable.html for a longer rant on the subject, complete with a couple of quotations to show that some philosophers really do think such silly things in the case of consciousness.)
- Asmodeus 17y ago
  (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 17y ago
    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.)

gjm11 17y ago

The alleged inference from "zombies are possible" to "physicalism is wrong" isn't quite what you say. It goes more like this. (1) If physicalism is correct, then (e.g.) mental states are identical to physical brain states. (Or something along those lines.) (2) But if A is identical to B, then A = B in all possible worlds; that is, A is necessarily the same as B. (3) Therefore, if physicalism is correct, then in no possible world are there zombies; necessarily, there are no zombies. (4) In other words, if it is possible that there are zombies, then physicalism is wrong. I think this argument is rubbish. Claim 2 seems like obvious bullshit, unless "identical" is given some weird technical meaning that makes claim 1 bullshit instead. Further, with the sense of "possible" that's relevant here it's very far from clear that anyone's shown that zombies are possible. (The SEP page treats this point quite well.) I have used the following parallels before: I can imagine electric current flowing without any charged particles being present, "therefore" electric current is not the same thing as the movement of charged particles; I can imagine my computer continuing to do what it does without its circuitry and what happens therein, "therefore" the processing my computer does is not a mere activity of its circuitry. What twaddle. (See http://www.mccaughan.org.uk/g/log/2007/inconceivable.html http://www.mccaughan.org.uk/g/log/2007/inconceivable.html for a longer rant on the subject, complete with a couple of quotations to show that some philosophers really do think such silly things in the case of consciousness.)

Asmodeus 17y ago
(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 17y ago
  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.)