On 6/14/2016 4:56 PM, Bruce Kellett wrote:
On 15/06/2016 5:22 am, Brent Meeker wrote:
On 6/14/2016 10:09 AM, Bruno Marchal wrote:
Let me explain shortly. First we start from consciousness, by
(re)defining computationalism as the assumption that there is a
level of description of myself such that my consciousness remains
unchanged through a functional substitution made at that level.
But already at the beginning you have swept the problem under the
rug. Notice that you could replace "consciousness" by "physics" in
the same sentence. You're just assuming that whatever you're talking
about can be computed - which is OK, but it's not solution to the
problem of consciousness until you can say exactly which computations
are conscious an which are not. I think it is interesting that you
consider spiders conscious, but not plants. What's the difference?
Obviously it's the degree and scope of interaction with the
environment. Which to me is further evidence that you implicitly
recognize there can be no sharp division between matter and mind.
I agree with you here, but I think that Bruno has an even more serious
problem: it seems that there is an inherent circularity in the above
computationalist account of consciousness.
The starting assumption is that consciousness is unchanged by a
functional substitution at some level. But what does a "functional
substitution" mean in this context? It is clear that Bruno is thinking
of replacing some or all of the human brain by a functionally
identical machine. Firstly, that assumes supervenience of
consciousness on the brain -- something that is not part of the
definition of consciousness.
But one for which there is good evidence.
And secondly, it assumes that a different substrate, one that can
instantiate computations independently of brains and consciousness,
exits.
Which follows from the Church-Turing thesis that all Turing universal
computers can compute the same set of functions.
If you are going to substitute something for something else, you need
something else by which to make the substitution. In this case, the
implicit assumption is that we have a physical computer that can be
used to carry out the required computations. But no such physical
machines exist if we start with consciousness in isolation.
That's not how I understand his argument. He does start from the
assumption that a brain's consciousness can be instantiated by any
machine that is Turing universal - what he calls the "Yes, doctor"
assumption. But then he tries to prove that the physical instantiation
is superfluous by constructing a thought experiment in which the
computation takes place with no corresponding physical changes of state
(see also Mauldin's Olympia argument). I don't think he succeeds in
this proof, but I don't think he considers it very important either. As
a neo-platonist he's already sure that numbers, arithmetic, and
computations are "more real" than material objects. So the immaterial
existence of computations is almost a given for Bruno.
Bruno wants to deduce the existence of the physical by some statistics
over computations going through the particular consciousness. But this
is viciously circular if he has to assume the existence of that
physical level at the start. He hasn't derived or deduced it -- he has
simply assumed it.
Bruce
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