To: Simon Y.
From: Geoffrey Klempner
Subject: Could you exchange bodies with someone else?
Date: 16 November 2007 12:15

Dear Simon,

Thank you for your email of 12 November, with your University of London Introduction to Philosophy essay in response to the question, 'Could you exchange bodies with someone else?'

I got a strong sense reading this essay that some hard thinking was going on here. You have really grappled with this question. If you can do this kind of thing in an exam (i.e. under pressure, when it is easy to fall back on things you've learned rather than relying on one's ability to think originally about a problem) then you will do very well.

An examiner might criticize the essay on the grounds that you have not addressed the questions Williams raises, concerning the seeming paradox that arises when we look at a brain swap scenario from different perspectives. However, the exam question didn't ask this so I think it would be unfair to penalize the essay for that reason. However, in that case you need to find sufficiently interesting things to say about the aspects of the problem that you pick up on. I think you do succeed in this.

The question looming over your discussion concerns the nature of personal identity. 'If... the self is just a logical construct, there is nothing to transfer; transferring the psychological makeup would be merely changing the psychological makeup of the recipient person and, the reverse process would be changing the psychological makeup of the initial donor person.'

One question we can ask is whether a 'self' which is a 'psychological construct' cannot be an 'entity with an identity'. Can't a construct be an entity?

Consider mathematics, where primitive notions (e.g. a set) are used to construct other abstract objects, such as numbers. There is no doubt that such constructed objects have an identity which can be clearly defined.

Or, suppose someone argued that a 'spatio-temporal object' is merely a logical construct out of molecules. The borderline where one body ends and another body begins, or the conditions under which we say that a body has been 'destroyed', depends on the way that we have defined 'spatio-temporal object'. Unlike mathematics, identity over time for material objects, such as a chair or an axe or a ship, is not precise but vague: there are central cases which are clear, and borderline cases where we do not know what to say.

The vagueness of questions of identity is a point you make towards the end of your essay. However, I would disagree that the question of identity or non-identity is, 'just an opinion'. It can be, when we are dealing with borderline cases. But there are plenty of examples where there is only one reasonable 'opinion' to take. I smash your grandmother's vase and, to make up for my carelessness, buy an 'identical' vase on eBay. Even if the vase I bought is indistinguishable from the original, it is not a matter of mere opinion that it is not the original. Whereas, if I had painstakingly stuck the pieces together, the result would be the original vase, although badly damaged.

So let's take a brain swap scenario, where there is not the least room for vagueness or doubt: my brain is switched with Mother Theresa's. Whether one looks at this from the subjective or objective viewpoint, there is no doubt that *someone* with Mother Theresa's body thinks he is GK, while *someone* with GK's body thinks she is Mother Theresa. It is possible to define a notion of personal identity (in terms of the spatio-temporal continuity of the material basis for consciousness and memory, i.e. combining spatio-temporal continuity with psychological continuity) which justifies the view that there has indeed been a 'body swap'. GK now has Mother Theresa's body and Mother Theresa has GK's body.

However, we don't *have* to do this, and I think this is your point. The concept of a 'person' just wasn't designed for such outlandish scenarios, and if surgery became sufficiently advanced to allow brain swaps, we would be faced with a genuine decision about which 'concept of a person' is the most faithful to the existing moral and social institutions in which the existing concept of a person is embedded. Indeed, there always remains the possibility of drastically altering those institutions -- making this an extremely difficult question to answer.

An alternative response (which Parfit gives in his book 'Reasons and Persons') is to say that the concept of a person is incoherent, and best disposed of. Not just because it is a construct, but because the attempt to define identity over time runs into insuperable difficulties.

As a footnote, I once asked my first two daughters when they were very young, 'If someone swapped your heads and each of you looked in a mirror, whose face would you see?' Each unhesitatingly replied that she would see the face of her sister.

All the best,

Geoffrey