Several list members cajoled me into reading David Parfit's "Reasons
and Persons". So I braved our dragon infested library, and sourced a
copy. I can see why his book is relevant to this list, particularly
part 3 of his book "Personal Identity". It was a good recommendation -
I can certainly recommend this as one of the background readers - too
late it missed the cutoff for my book :)

However, there was one thought experiment that concerned me, and it
relates to his notion of psychological spectrum. We are to suppose
that it is possible to generate psyches in between our mind and that
of Napoleon Bonaparte, by progressively swapping in neurons from NB's

Since we have a number of closet computationlists here, I paraphrased
the thought experiment as what if we swapped the transistors in my PC
for that of a (old-style PPC) Mac. At first, there would be little
difference, and the machine would be indistinguishable from that of a
PC - save a few bugs (anyone remember the Pentium division
bug?). Similarly, at the other end of the spectrum, the machine would
be virtually indistinguishable from a Mac. But what about the machines
in the middle? Surely these machine would simply be
non-functional. Replacing PC transistors with Mac transistors would be
no different from simply disabling the PC transistors - eventually a
critical path would be severed, and the machine would be defunct.

No two human brains are wired identically - indeed our daily
experience updates the connections between our neurons. Gradually
replacing neurons in our brain by someone else's neurons would have
the same effect as simply removing neurons one-by-one. For a while,
there would be little noticable effect - brains are, after all quite
robust against damage. But eventually, and well before the magical 50%
mark I would suggest, the structural organisation of our brain would
be lost, and we'd lose consciousness.

Since quite a bit of Parfit's later arguments depend on this
psychological spectrum thought experiment, it seems some of his
identity issues aren't in fact problems at all. Anyone have a comment
on this, or is it all obvious philosophy 101 stuff that I missed.


A/Prof Russell Standish                  Phone 8308 3119 (mobile)
Mathematics                                    0425 253119 (")
UNSW SYDNEY 2052                         [EMAIL PROTECTED]             
            International prefix  +612, Interstate prefix 02

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