To: Marc E.
From: Geoffrey Klempner
Subject: Philosophical significance of zombies
Date: 13 May 11:59

Dear Marc,

Thank you for your email of 13 April, with your first essay for the Philosophy of Mind program, in response to the question, 'What is the philosophical significance of the idea of a 'zombie'?'

This is an excellent piece of work.

It is worthwhile distinguishing, as you have done, different kinds of philosophical 'zombie' and also different varieties of 'possibility'.

You correctly identify the 'physical zombie', identical at the molecular level as the one to use against physicalism. I wonder, however, whether the other notions of a zombie - the behavioural or functional - might yet have a role to play in the argument. For example, suppose we buy the 'property dualist' account, according to which the subjective, phenomenal aspects of consciousness are related to physical properties via 'psychophysical laws'. On this theory, a silicon version of you might, for all we know, be a zombie but we can never tell, because there is no way to test whether the psychophysical laws fail or not.

Meanwhile, your silicon simulacrum is asking the very same question. Maybe silicon is the element with the power to bring phenomenal consciousness into being, and all the carbon human beings are zombies.

Another point is that if property dualism allows for the possibility of a zombie, then there seems to be little to distinguish this theory from epiphenomenalism. The same paradox arises of the zombie philosopher who declares, 'I know I have phenomenal consciousness'. He must 'say' this - or, rather, utter those same sounds - because, by hypothesis his non-zombie double says it and means it. Strange!

These are not knock-down arguments, but they do give grounds for the suspicion that the zombie hypothesis, however attractive it may seem, is in fact incoherent.

How can one show this? Is there a proof one can give? Let me continue to chip away.

You say you know what you mean by 'phenomenal consciousness' because you are aware of it now, at this moment. Moreover, you are aware that its quality does not change abruptly or oscillate like a faulty television set, but remains constant from moment to moment. But how exactly does awareness tell you this?

Consider the logical possibility that the spectrum of your phenomenal consciousness of colours inverts every second, but your memory is systematically misleading you into thinking that no change has taken place. (Wittgenstein 'Philosophical Investigations' Part II page 207: 'Always get rid of the idea of the private object in this way: assume that it constantly changes, but that you do not notice the change because your memory constantly deceives you.')

Is it improbable that your memory - which has shown itself to be pretty reliable in other contexts - is deceiving you? How does one measure probability in this context?

If you find that thought too fantastical, you have my sympathy. Surely this is a case like G.E. Moore's famous 'Here is a hand, and here is another hand' ('Refutation of Idealism') whether the alternative sceptical possibility is just impossible to take seriously, impossible to 'mean'. - Then consider a less extreme possibility. Over the years, with advancing age, the colours have not altered but merely dimmed slightly, while my memory has adjusted to compensate, so I am thankfully not aware of any difference. The statement, 'Grass still looks as green to me as it ever did' is false, although I sincerely believe it to be true.

I have a powerful motive for being opposed to the physicalist picture of the universe. It seems to me that there could have been a universe physically just like this universe, with a human being just like GK in it who was not I. The alternative GK is not a zombie. We are the same physically and mentally. The only difference is in sheer identity. He is he and I am I.

Alternatively, in Nietzsche's 'Eternal Recurrence', one of the infinitely recurring GKs is I - the present one, the one writing these words now - while all the other qualitatively identical but numerically distinct GKs are not I.

It is a good question for me, why do I find this argument so compelling, while I reject the zombie argument? (Nietzsche clearly thinks that not just GK but I will 'return'. Does Nietzsche see something that I have missed?)

Unlike the zombie argument, the 'GK who is not I' hypothesis does not involve belief in 'private objects' in the sense attacked by Wittgenstein. That is the one positive thing in its favour. I wish I could say more, but I don't think I can.

All the best,

Geoffrey