There has been a surprising amount of talk about zombies recently around the blogosphere. Here I thought the zombie issue was settled back in the ’90’s; but I suppose that’s what I get for forgetting that there aren’t any solved problems in philosophy, and it is in the nature of zombies to come back from the dead so I suppose I shouldn’t be all that surprised.
At any rate this zombie flare-up was brought about by Richard Chappell’s argument against physicalism. It starts by claiming that there is a possible world where there are creatures exactly like us in every physical way but who lack conscious experience. They scream when stabbed and ohh and ah over Matisse but ‘all is dark inside’; they are merely going through the motions since they do not have any conscious mental experiences. Since this world is conceivable it is metaphysically possible and since this world is metaphysically possible that means that physicalism about consciousness is false. This is, of course, not new with Chappell; this is the argument developed by David Chalmers. Chappell then presses JAckson and Chalmers’ argument that the popular Kripkean response fails to meet the zombie challenge. He argues that the zombie world is conceivable and whatever we decide about the way we want to use our words (i.e. whether we decide to apply our word ‘consciousness’ to the zombies), the metaphysical possibility of that world is enough to refute physicalism.
I have been arguing that Chappell’s argument fails to address the most plausible physicalist response to the zombie argument (and that his defense of modal rationalism itself adopts a version of the Kripkean strategy). This is to deny that the zombie world is actually conceivable. Sure, it seems to Chappell that he is imagining a world where there are physical duplicates of me (or you) and no consciousness but he is really imagining a world that LOOKS a lot like there are physical duplicates of me (or you) which lack consciousness. This is what I have been calling the Kripkean response because it is exactly the strategy that Kripke adopts in Naming and Necessity. It seemed to people that they were imagining a world where water wasn’t H2O (or where Aristotle wasn’t Aristotle) but they are really imagining a world where there is stuff that LOOKS like water does to us which isn’t H2O (or a world where there is a person who LOOKS like Aristotle (or satisfies most or all of the descriptions that Aristotle satisfies in the actual world) who isn’t Aristotle). Why should we think this is really what is going on? There are many reasons:
1. Do Conscious Mental States Cause Behavior?
If the answer to this question is yes then it is obvious that zombies are inconceivable. The zombie world is a world physically just like ours but which lacks conscious experience. Conscious experience act as causes of behavior, so a world that lack them would not be one where things went on as usual. It would be a world that was missing a bunch of causes and so, if just like ours, would have creatures that looked like us but would not act just like us. This is basically the argument that John Perry developed in his “Knowledge, Possibility, and Consciousness”.
2. Do We Have Epistemic Access to Our Conscious Mental Experience?
If the answer to this question is yes then the zombie world is inconceivable. This is the argument developed by Robert Kirk in his book “Zombies and Consciousness” (and the one being talked about over at Overcoming Bias). Here is a quick summary of the argument (from my review of the book for phil. psych.)
The anti-zombie argument can be stated rather easily. According to the ‘zombist’ there can be a creature that is a molecule-for-molecule-duplicate of me and yet lacks phenomenal consciousness. At the same time they want to hold that we have ‘epistemic access’ to our phenomenal consciousness. These two claims are not consistent with each other. To see why, imagine a zombie world that is identical to ours except in respect of phenomenal consciousness. Since that world is just like ours we can assume that it is causally closed under the physical. Now, continues Kirk, it should be possible to add to that world whatever it is that the zombist thinks will transform it into a world that does have phenomenal consciousness. But since whatever we added would have to be nonphysical, since their world is identical to ours (excepting consciousness), and so could not interact causally with the physical world (which is closed under the physical), it follows that we could not know anything about these ‘e-qualia’. Therefore, we could not have ‘epistemic access’ to them.
To make this vivid he offers what he calls the ‘sole-pictures’ argument. Again, consider our zombie world. Let’s add whatever it is that the zombist thinks will transform it into a world like ours. Now let’s imagine that by a “strange shift in the natural laws” of the zombie world the visual processes that in me cause e-qualia instead cause
sequences of constantly changing pictures to appear on the soles of [the zombie twin’s] feet. The changing colored patterns on his soles are isomorphic to those neural process in the same way as my e-qualia are isomorphic…to similar process in my brain. (p. 45)
Is there any reason to think that the zombies will have any access to these sole-pictures? Kirk’s answer is ‘NO!’ If not then zombies are not conceivable. The zombist commits what he calls the ‘jacket fallacy’: They treat qualia as something that can be stripped off a world without changing anything in the way that I can remove a jacket and remain the same. In the second half of the book Kirk tries to construct a theory of perceptual-phenomenal consciousness that does not commit the jacket fallacy.
This argument is convincing to me, and others. Has anyone responded to it?
3. Do qualitative properties (partially) Constitute our Phenomenal Beliefs?
If the answer to this question is yes then zombies are inconceivable. This is the option that Chappell and Chalmers opt for. They argue that qualitative properties are epiphenomenal in that they do not causally interact with the physical states of my brain but since the partly constitute the phenomenal beliefs I have (or in other words, my beliefs about what phenomenal states I am in). My zombie twin will believe that he sees red when I do but whereas I have a belief whose content is partly constituted by the epiphenomenal non-physical property ‘redness’ (or whatever), my zombie twin’s phenomenal beliefs lacks this property entirely and so we have very different beliefs even though we are physically identical. This seems conceivable and so it may seem that this response avoids the kind of physicalist response I am suggesting. But this is too quick.
The reason it is too quick is because of the discovery of pain asymbolia. Pain asymbolia is a rare condition where people report that they are in pain, and can even tell you what kind of pain it is (burning, pinching, stabbing, etc) yet they do not feel it as painful. The distinctive painfulness of the pain is absent. Presumably then these patients have an our world equivalent of the kind of beliefs that Chappell and Chalmers take the zombies to have. But far from acting in the same ways that we do when we have the same beliefs + qualitative painfulness these pain asymbolics laugh and smile at the pains. So the world that Chappell is imagining is not physically just like ours. If it were then the zombies would not behave in all the same ways that we do.
All of these discoveries come from a posteriori investigation. Even on Chappell’s modal rationalism these all turn out to be a posteriori discoveries because they depend on which world is actual. A purely rational being would not a priori whether the answers to 1-3 were ‘yes’ or ‘no’ until looking at the world. This is the Kripkean strategy. Chappell hasn’t argued against it and it doesn’t fall prey to the arguments he does develop.