To: Sue B.
From: Geoffrey Klempner
Subject: Personal identity and body duplication
Date: 19th January 2009 12:33

Dear Sue,

Thank you for your email of 6 January, with your second essay for the Possible World Machine, in response to the question, 'What thought experiments concerning body duplication show is that the concept of personal identity is ultimately dispensable.'

I can see that you have worked really hard at this, coming at the question of body duplication from every possible angle.

I won't argue with your assertion that 'we do have 7 bodies - 7 levels of existence through to the most enlightened'. That is a factual claim, whose basis we do not need to go into.

One response to thought experiments of body duplication which I can see you are very strongly tempted to (and which is consistent with the '7 bodies' theory) is to say that the self or person -- that is to say, GK or SB, is a physical body PLUS something else. Call this something else a 'soul'. On this view, a soul is an entity with an identity. The soul is 'the same' at different times. It persists, has an identity, through time. When I wake up in the morning, am aware of an 'I' which is the same 'I' that I was aware of before I went to sleep the night before.

One problem with this view, which relates to the 'Buddhist approach of momentariness' which you mention in your essay, is that there is no difference between saying that the soul which you had when you went to sleep is 'the same' or 'not the same' as the soul which you have when you wake up. You have the same memories (e.g. your first day at school) but having the same memories is not sufficient for being the same soul.

The philosopher Kant (in the 'Paralogisms of Transcendental Psychology' in the second part of the 'Critique of Pure Reason') put forward the counter-argument that souls are like colliding billiard balls, each momentary soul passing its states on to the next. Kant's point was not scepticism but rather that there simply is no logical difference between the two hypotheses. In other words the term 'soul' has not yet been given a coherent definition, nor does it seem likely that such a definition can be given if we assume from the start that a soul is an entity which is separable from body (whether this be a human body or some physical entity perhaps lodged inside the human body as Scientologists apparently believe).

Thus, anything physical can in principle be duplicated. Physical things are by definition located in space. The only way a soul can escape the possibility of duplication is by not being physical. However, the absence of physicality renders the soul susceptible to Kant's argument: for a non-physical soul, non-identity would logically be the same as identity.

You mention Leibniz's thesis of the 'identity of indiscernibles', correctly pointing out that the thesis only applies if we do not count spatial position as an identifying property. Kant's argument against the soul works because we assume from the start a spatial as well as a temporal dimension.

Another thought which you consider is that there might be multiple 'I's provided that each 'I' existed in a different world. This is actually very close to a hypothesis which Nietzsche put forward, which he originally derived from the Greek Stoics, the 'theory of eternal recurrence'. According to this theory, there is only a finite amount of matter in the universe, and therefore only a finite number of possible ways in which material particles can be combined. Given the assumption of determinism, if at any time a combination of all the particles in the universe is reached which is identical to a previous combination, then from that moment on history necessarily plays out the very same sequence as it played out the previous time. It follows that you will live the identical life (and have lived the identical life) an infinite number of times.

The burning question, however, is whether all the SB's are YOU. Nietzsche assumes that they are. At any rate you have to believe this in order to feel the full force of the doctrine of eternal recurrence (Kundera's novel 'The Unbearable Lightness of Being' vividly describes the difference between the two possible views of existence -- my life as evanescent and gone forever when it's gone, and my life infinitely repeated).

My view would be that this alternative could only appear 'real' if you believe in the identity of 'the soul' over time. On the hypothesis of momentariness, there is no recurrence, not even from one day, or one moment to the next.

What is there left? Just the physical person. The essay asked whether the concept of personal identity is dispensable. I would argue that it is not. In the society in which we live, the identity of the physical person is considered of utmost importance. (Consider what 'marriage' would be if personal identity was not considered important.) We do not, as it happens, have the power to duplicate physical persons. But if we did, then admittedly the concept would come under considerable strain. However, that is not sufficient reason in itself for throwing the concept overboard. (However, for a radically different view see Derek Parfit's book 'Reasons and Persons'.)

All the best,

Geoffrey