To: Sean R.
From: Geoffrey Klempner
Subject: The philosophical significance of zombies
Date: 8th September 2011 13:37

Dear Sean,

Thank you for your email of 29 August, with your essay for the first three units of the Philosophy of Mind program, in response to the question, 'What is the philosophical significance of the idea of disembodiment and/or the idea of a zombie?'

Although you perhaps did not see this yourself, the argument in your essay implies that there are in fact two notions of 'philosophical' zombie (in contrast to Night of the Living Dead type zombies). This was in fact a serious lacuna in the program, a point that I did not fully appreciate when I wrote the units.

The crucial stage in your essay is where you say, 'If we could identify a body, a zombie, which responds normally to outside stimuli, we would therefore seemingly have discovered a model that directly conflicts with the materialist's vision of the mind-body state...'.

Think about this for a moment. How on earth would such an experiment be possible given that, ex hypothesi, 'the zombie functions... as a 'normal' human being would by appearing to make conscious decisions...'? By hypothesis, everything I do or can do, my zombie double does or can do. There is no physical or behavioural clue which would enable an investigator to tell us apart!

Hence the point about the internal thought experiment which you go on to describe. Your account can be criticized on the grounds that what you have described would be fully consistent with amnesia. As a matter of fact, it is not uncommon to wake up in bed wondering what on earth you did at last night's party because you can't remember a thing. Hence the attempted description in the unit of an experience of (semi-) zombiehood actually in process. I wouldn't like to say if this description is coherent or not.

In fact, it doesn't matter (as I go on to argue) whether or not the description is coherent because you can't argue for mind-body dualism merely on the basis of a description of a 'possible experience' (i.e. the experience of disembodiment or the putative experience of semi-zombiehood). That is because there will always be alternative explanations. We are looking for a proof, either a proof of materialism or a proof of dualism, and nothing less will do.

So far, so good. But there was something I didn't think about. I strongly suspect that philosophers who rely on the zombie thought experiment (such as David Chalmers) assume, possibly implicitly, that zombies would exhibit certain behavioural defects or inexplicable failings, perhaps quite subtle (not like Romero).

Now the argument moves over to an entirely different level. What the sceptic about materialism would be saying, on this new version of the zombie thought experiment, is that *we just don't know* at the present level of neurophysiological or behavioural research whether there might not be 'zombies' in the third, 'in between' sense, persons who apparently behave quite normally, but on closer examination lack certain vital albeit subtle features, features which only the possession of consciousness can explain.

The first, 'pure', notion of zombie which I describe in the program goes together, not with Cartesian mind-body dualism, but rather with a version of mind-body dualism known as 'epiphenomenalism'. With pure zombies, there is no process of interaction. Everything that the body does is fully explained in materialist, causal terms. However, according to the epiphenomenalist, the physical processes going on in the brain *also* produce, as a by-product, the conscious states that I experience. My zombie double is my exact physical duplicate, but in its case, no conscious states are produced. In other words, consciousness is an 'epiphenomenon', it has no causal role in the production of observable behaviour.

My argument against epiphenomenalism is that if I am persuaded (by whatever means) that epiphenomenalism gives the correct account of the mind-body relation, then my zombie double will claim (perhaps I should put that in scare quotes, 'claim') to be an epiphenomenalist also. This is not a knock-down refutation of epiphenomenalism, but it is pretty persuasive.

On the other hand, if we are dealing with the third, 'in between' variety of zombie, then there does arise a possibility of a genuine difference between myself and my zombie double, detectable by means of objective observation, a difference which can only be explained in Cartesian mind-body interactionist terms. Such a discovery would count as an experimentally based, scientific case for Cartesian dualism.

This is all empty speculation you would say. (I would say that also.) However, the mere possibility of such a discovery, which we cannot rule out a priori, is arguably sufficient the sceptic would say to cast doubt on materialism. You can't claim to know that materialism is true, a priori, if you are unable to disprove the possibility that there is *something* we-know-not-what which is required in addition to a fully functioning human brain, in order to be fully human.

All the best,

Geoffrey