On 6/14/2016 9:33 PM, Bruce Kellett wrote:
On 15/06/2016 2:11 pm, Brent Meeker wrote:
On 6/14/2016 7:18 PM, Bruce Kellett wrote:
On 15/06/2016 11:55 am, Brent Meeker wrote:
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.
Sure, but is that part of the definition of consciousness?
I don't think he ever intended to define consciousness. He assumes
everyone knows what it is, i.e. ostensive definition.
Just pointing to a conscious person does not specify what
consciousness is, or its limits. Much less does it indicate that
consciousness is a kind of computation.
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.
No, the existence of an independent substrate does not follow from
the Church-Turing thesis. That thesis merely states that *if* you
can implement a Turing machine on a different substrate, it will be
able to compute the same functions. That does not require that any
such substrate exists.
But we already know that substrates exist that will support a
universal Turing machine (modulo infinite memory tape), i.e. digital
computers. Turing imagined his machine to be implemented by pencil
and paper and a set of instructions.
That seems to be assuming a lot! Assuming that consciousness is a
(type of) computation does not imply that non-arithmetical substrates
exist, much less that pencil and paper exist. Knowing that something
is true of the world that we experience does not entail that its
existence is necessary.
Bruno can start from his (neo-)platonist assumption that arithmetic
exists independently, and that arithmetic implements all computations
(Turing machines). But he then has to prove that this assumption leads
necessarily to the existence of a physical world of the character that
we observe.
I think that parts pretty easy. Having assumed arithmetic exists it
follows from Godel that all Turing computations exist (in arithmetic).
Among all computations are those instantiating our conscious thoughts.
Those conscious thoughts include those we call perceptions which we
interpret as experience of a physical world.
As I said this seems to have the same problem as Boltzmann's brain. It
would imply that any universe at all similar to ours has measure zero.
But eternal inflation may have the same problem of "proving to much".
Since his 7 steps only work if the physical world is already assumed,
he has to look to some other arguments. I don't think you can argue
that the physical world is assumed in Bruno's 7 steps as part of a
reductio argument -- that this assumption leads to a contradiction.
He thinks it leads to an absurdity - that the computation is implemented
just by indicating the frames of the movie graph. No physical change of
state. No entropy increase. A related question is whether or not
replaying a record of a conscious instantiating process again
instantiates the consciousness?
Brent
In the first place, the reductio fails, and even if it succeeded, one
could well claim the assumption of platonism was the root of the
contradiction, leaving physicalism unscathed.
Bruce
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