On 19 Aug, 01:51, Brent Meeker <meeke...@dslextreme.com> wrote:

> I think you are right that the MGA is at the crux.  But I don't know whether 
> to regard it
> as proving that computation need not be physically instantiated or as a 
> reductio against
> the "yes doctor" hypothesis.  Saying yes to the doctor seems very 
> straightforward when you
> just think about the doctor replacing physical elements of your brain with 
> functionally
> similar elements made of silicon or straw or whatever.  But then I reflect 
> that I, with my
> new head full of straw, must still interact with the world.  So I have not 
> been reduced to
> computation unless the part of the world I interact with is also replaced by 
> computational
> elements (I think this problem is swept under the rug with the phrase "at the 
> appropriate
> level of substitution").  So suppose the doctor also emulates all the world 
> that I will
> ever interact with.  Now it is not so clear that such an emulation is 
> computable, but
> suppose it is.  Now my consciousness is entirely emulation - but it is also 
> entirely in
> another, emulated, world.  In that world it is physically instantiated.  So 
> it has not
> been shown that the emulation can be uninstantiated mathematics.

Our last two posts crossed in the ether!  Yes, I've wondered about the
possible reductio element in yes doctor - like it's sometimes
forgotten that Schrödinger's poor old tabby was originally proposed as
a reductio against the Copenhagenists.  But I'm not sure I agree that
"computation need not be physically instantiated" is strong enough -
MGA is more dismissive of PM than that (Bruno sometimes says that
appeals to PM are 'spurious' with respect to CTM).  I think that the
strong entailment of MGA is CTM + PM = false, and that yes doctor is a
promissory note against some future theory of substitution (with the
caveat that it won't be complete).

David

>
> Brent
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