Descartes and I

I made a similar argument as a comment on Scott's blog. Surprisingly, not everybody believed it 8-).
But I think my responses were not that bad [1, 2, 3].
The following is a summary, in case you do not want to click through those comments:

I cannot doubt that I am, however I can doubt that my brain (or any other computational device) exists.
It follows that I cannot be my brain.

Descartes’ argument is really just two statements:
1) There is a function D(x) equal to my doubt about x. Let’s say D=0 means I cannot doubt x and D>0 means I can have doubts or actually have doubts.
2) from D(I) =/= D(B) it follows that I =/= B.

There is an important issue with 1), because my doubts D(x), in general, change over time. However, Descartes’ argument is that such a change in doubt is not possible for I and B: I cannot doubt that I am, but there will always be some doubt about B.

But let us assume you can convince me that I = B, in other words I am my brain. Now let me imagine a hypothetical supercomputer S in the future, which is capable of simulating human brains and in particular exactly emulates my brain B.
Will you also try to convince me that I = S , although it is clear that B is not S?

Notice that this hypothetical supercomputer S is constructed so that every argument b1, b2, … in favor of I = B has an equivalent argument s1, s2, … in favor of I = S.
The only way to avoid a contradiction (I=B and I=S but B is not S) is to argue that S does not really exist, it is only imagined.
But this is exactly Descartes' argument: We reject I = S because we have doubts that S may exist.

added later: After some more back and forth I summarized my argument in this final comment.


Lee said...

It would make more sense to me if your argument were put in terms of a subset of the chemical reactions that go on in the brain rather than the brain itself. You die when that subset of chemical reactions stops, but the brain itself (the piece of meat) persists for at least some period of time after you die.

So is your interest in mind-body duality mostly a result of your interest in the foundations of quantum mechanics?

wolfgang said...


you can replace "my brain" or B in the argument with "process in my brain" or "chemical reactions that go on in my brain".
It would not change the argument.

Yes, my interest in the mind-body problem mostly began with questions about the interpretation of quantum theory.