Re: A calculus of personal identity

From: Stathis Papaioannou <>
Date: Sun, 25 Jun 2006 18:51:49 +1000

Bruno Marchal writes:

> > Lee,
> >
> > It’s perhaps unfortunate that we are arguing about this because I
> > think we basically agree on what Derek Parfit has called a
> > reductionist theory of personal identity (in his 1984 book “Reasons
> > and Persons”; apparently “reductionist” was not in wide use as a term
> > of abuse back then). I like to emphasize the instantaneous or granular
> > nature of personhood not because we literally die and are resurrected
> > every moment, as those words are commonly understood, but because it
> > would make no significant difference to our stream of consciousness or
> > sense of self if in fact this were the case. Although in our
> > experience the sequence of mental states making up an individual’s
> > stream of consciousness always occur in the one brain, the brain does
> > not provide any special “glue” joining the mental states together, and
> > no such joining is necessary. Two or more mental states are
> > experienced as part of the one stream of consciousness if their
> > content is related in a particular way, like elements in a set. How,
> > where and when the mental states are implemented is irrelevant and
> > unknowable from a first person perspective, unless it actually affects
> > the content of the mental states.
> >
> > Hal Finney in his recent thread on teleportation thought experiments
> > disagrees with the above view. He suggests that it is possible for a
> > subject to apparently undergo successful teleportation, in that the
> > individual walking out of the receiving station has all the
> > appropriate mental and physical attributes in common with the
> > individual entering the transmitting station, but in reality not
> > survive the procedure. I have difficulty understanding this, as it
> > seems to me that the subject has survived by definition.
> I mainly agree with you but I would not have ended with "by
> definition". I would have mentionned instead the comp *assumption* and
> perhaps also the serendipitously good choice of the correct level of
> substitution.
> From a logical point of view it is consistent (possible) that the one
> reconstituted is a zombie (although this would contradict comp or the
> choice of the level).

It depends on what we mean by "all the appropriate mental and physical attributes". If the reconstituted person is a zombie then he is certainly lacking some mental attributes that the original had, assuming the original was not a zombie. Of course, it is not possible for a third person observer to be certain about first person mental states, and this would apply to our teleportee: he may feel as if he is the same person as he was prior to the procedure, but he might be wrong. The flaw in this argument is that the same considerations hold if he had travelled by train: he may look and feel like the same person, have all the appropriate memories, and so on, but how does he know that the original didn't die during the journey, to be replaced by a copy as would have happened had he teleported? In a sense, this is just what did happen, since over minutes to hours most of the matter comprising neural synapses is replaced, while over months most of the matter in a human body is replaced.

If there is some sense in which a person's identity might be lost despite his physical and mental attributes being apparently preserved (and I'm not sure the idea is even coherent), there is no reason for nature to waste effort evolving and maintaining such an identity-conservation system, because it cannot make any difference to behaviour.
> Comp itself cannot be proved but what can be proved is that IF comp is
> correct then comp cannot be proved, necessarily. So we have, somehow,
> to be open to non-comp beliefs.
> Put in another way: if you survive when saying YES to the doctor, you
> have to respect those who say NO to the doctor (unless you have bad
> intentions of course or are ignorant).

The falseness of comp (or functionalism) does not necessarily mean duplication would be a death sentence. If our consciousness is dependent on the activity of tiny black holes in the microtubules, or whatever, then we might be able to survive duplication if our new brain had the right sort of tiny black holes in the microtubules. The test is that the duplicate have subjective experiences sufficiently close to those of the original: if that is the case, then I would say by definition the person has survived.
> Parfit has not see this, and that is why he dares to qualify (a bit
> provocatively I would say) his identity theory as a reductionist
> theory, or "the reductionist theory". With comp (when made explicit)
> Parfit's theory is mainly correct except on two points:
> 1) What I have just said: the theory is not reductionist---It is the
> contrary: it provides (by diagonalizations!) many vaccine against many
> form of reductionism. After dinner ;) I could even go as far as to say
> it gives a path toward that Unconceivable Freedom described by some
> mystic like Vimalakirti!
> 2) We are type, not token. There is no physical token. (with comp).
> Parfit thinks we are token. I have not the Parfit under the hand, I
> will give you the pages later. I don't think there are any mathematical
> token either. It looks like Parfit makes us token for avoiding
> immortality at the start.

You may be referring to chapter 99 of "Reasons and Persons". A "token" is a particular instantiation of a person, while a "type" is the set of related instantiations (these terms are actually attributed to the philosopher Bernard Williams). As I read him, Parfit says that we are each token, but the significance we attach to our lives and those of others we care about must be attached to a type rather than a particular token. Thus, in destructive teleportation, a token is destroyed, but the type survives.
> To sum up, Hal Finney seemed to me coherent, giving that in its recent
> post he admits questioning comp. It is less clear for me how he can
> still use Kolmogorov complexity (a computer science notion), but still,
> logically that could make sense, perhaps through some Powerful Oracle
> resource (actual infinity of highly uncomputable information). I don't
> know. Hal?

Hal promised to explain how a person might not survive destructive teleportation despite being apparently subjectively and objectively unchanged, and I look forward to this.

Stathis Papaiaonnou
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Received on Sun Jun 25 2006 - 04:52:50 PDT

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