To: Graham H.
From: Geoffrey Klempner
Subject: Personal identity and body-duplication
Date: 20th May 2011 12:53


Essay on personal identity
Dear Graham,

Thank you for your email of 8 May, with your second essay for Possible World Machine in response to the question, 'Imagine you are Mike Harding. As you lie injured on the road, you are told that a brain scanner is going to be used to map your memories and personality and the information used to program the brain of a new body cloned from one of your own cells. The moment the new 'you' gains consciousness the old 'you' will be painlessly destroyed. How do you feel about this prospect? Justify your answer by reference to one of the competing philosophical accounts of the relation between mind and body.'

I liked the way you pitched this, with a reference to the Don Siegel film, 'Invasion of the Body Snatchers', because it raises an issue -- the question of qualia -- which seems to be central here: the question being whether Mike Harding's replacement *has* qualia, or, if he does, whether these are indeed the *same* qualia.

I don't actually think that this is the decisive question in the present case, but it is important because it reveals what we are tempted to say about the scenario.

You state that you are going to 'assume that the true nature of the mind-body problem is the one stated by the physicalists'. You don't say which version of physicalism or materialism you subscribe to: the 'eliminative' or the 'non-eliminative'. Eliminative materialists believe that all the truths about human psychology can, in principle, be translated into the language of physics, while non-eliminative materialists hold to a non-reductionist view according to which statements about human psychology are 'supervenient' on physical states, meaning, that there can be no difference in psychological state which is not reflected in a corresponding difference in physical state.

On either view, however, the very existence of qualia is problematic to say the least. This is obvious with eliminative materialism, but I have seen defences of the notion of qualia by non-eliminative materialists. I'm not convinced, but the idea would be very close to what I would describe as epiphenomenal dualism -- which denies the dualism. Physical states of the brain have a mental aspect which is not distinct from those states (identity not dualism) and yet cannot be deciphered or read or discovered by any amount of examination of those physical states.

Crucial to this notion of 'physical qualia' is the claim that it would be impossible, in principle, for the very same physical state (say, in me and my double on twin earth) to produce 'different' qualia. In other words, there is no question of speculating whether my double has 'my' qualia, or is a 'mutant' (to use your term) or indeed a zombie with 'nothing on the inside'.

I like Nagel's idea that there is something which I know, as the unique possessor of my brain, which could not in principle be known by any other subject. You'll find an elaboration of this idea in my paper, 'Truth and Subjective Knowledge' http://klempner.freeshell.org/articles/shap.html. However, I don't see this as in any way defending the idea of qualia. Subjective knowledge isn't a judgement about some internal subjective 'object' (which would be a 'private object' in Wittgenstein's sense) but rather a way of being in relation to the world, which no other subject can share.

The problem with qualia is that they obey no rules whatsoever. I can speculate whether my double on twin earth has qualia like mine or different to mine, or has no qualia at all. But then I can ask the very same question about myself, when I started typing this letter. My present memory tells me nothing. 'Always get rid of the idea of the private object in this way: assume that it constantly changes but that you do not notice because your memory constantly deceives you' (Wittgenstein). The point is similar to the argument that solipsism always shrinks to solipsism of the present moment.

My exact physical double would necessarily have my memories, according to the supervenience thesis (non-eliminative materialism). Could there be any difference, at all? You speculate that there is something unique about 'experience', such that the the very same memory state would be different in the two cases (say, Mike Harding and Mike Harding's replacement) because Mike Harding's memory is somehow connected to an experience which actually happened, whereas the memory of his replacement is not. But how would this difference be manifested, on a physical level?

One important point which is emphasized in discussions of personal identity is the role of causation. If I died and, through sheer cosmic accident a version of me appeared on twin earth, the causal link between my experiences and the memories of my twin earth double would be lacking. However, in the case of Mike Harding and his replacement we *do* have a causal link, in the process whereby Mike Harding's memories are recorded and uploaded into Mike Harding's replacement. Which makes the question whether there is, indeed, any difference between Mike Harding and his replacement very difficult to answer, for the physicalist at least.

In case you're interested, there is a very useful discussion of the question of personal identity and Mike Harding-type thought experiments in the last issue of Philosophy Pathways ('Parfit, Lewis and the Logical Wedge: Fusion-Fission's Challenge to Coextension' by Oliver Gill). I don't have a satisfactory answer to the puzzle. I share your intuition that I wouldn't want to be 'replaced', that this would be the same as death (without resurrection). Yet it is difficult to find arguments to back up this view.

All the best,

Geoffrey