On 20 Aug, 10:05, Bruno Marchal <marc...@ulb.ac.be> wrote:
> On 20 Aug 2009, at 02:07, David Nyman wrote:
>
>
>
>
>
> > 2009/8/19 Jesse Mazer <laserma...@hotmail.com>:
>
> >>>>> I completely agree that **assuming primary matter** computation  
> >>>>> is "a
> >>>>> physical process taking place in brains and computer hardware".  
> >>>>> The
> >>>>> paraphrase argument - the one you said you agreed with - asserts  
> >>>>> that
> >>>>> *any* human concept is *eliminable*
>
> >>>> No, reducible, not eliminable. That is an important distinction.
>
> >>> Not in this instance. The whole thrust of the paraphrase argument is
> >>> precisely to show - in principle at least - that the reduced concept
> >>> can be *eliminated* from the explanation. You can do this with
> >>> 'life', so you should be prepared to do it with 'computation'.
> >> Well, not if you believe there are objective truths about  
> >> computations that
> >> are never actually carried out in the physical world, like whether  
> >> some
> >> program with an input string a googolplex digits long ever halts or  
> >> not.
>
> > Yes, but here - in connection with Peter's apparent support for the
> > Quinean concept-reduction argument - I was specifically commenting on
> > the status of 'computation' **if** you assume primitive matter.  In
> > that case, I'm not sure what "never actually carried out in the
> > physical world" would mean.
>
> On the contrary. If you assume there is a primitive material reality,  
> a primitive physical universe, then it makes sense to talk about the  
> computations which are carried out in the physical universe, like the  
> one done by this or that computer or brains, and the computations  
> which are not done in that universe, like some possible  
> counterfactuals (the computations carried out by Julius Caesar meeting  
> Napoleon), or some extravagant computations like the computation of  
> the 10^(10^1000) digit of the square root of two.

Yes, of course you're right - perhaps I didn't phrase my response to
Jesse clearly enough.  In my discussion with Peter about Quinean
'eliminative paraphrasing', I was pursuing the same conclusion that
you attribute to Dennett as an 'honest materialist'.  That is, under
materialism, that persons, consciousness - and computation - must in
the end be explained away, or conceptually *eliminated*.  I'm not
saying that I hold these views (I emphatically do not), only that
anyone who honestly and rigorously adheres to materialism must see
that  they are entailed by this position.

Of course, under materialism, there is a *physical process*
corresponding to 'computation'; consequently, as both you and Jesse
point out, one can of course envisage non-occurring, or
counterfactual, processes with respect to these.  But I don't see how
that would change the conclusion of the eliminativist argument I was
pursuing (as devil's advocate) - as indeed Jesse pointed out to Peter.

> > I don't have a problem with step 8 on the basis of the Olympia
> > argument, as I've tried to demonstrate - is there some other aspect of
> > computational supervenience that you feel I'm missing?
>
> >> May be you don't want to do the math? The math for UDA are really
> >> basic compared to the math needed for AUDA.
>
> > I'm trying to follow the math as you go through it, although I still
> > haven't really fathomed where it's leading.
>
> Your second sentence answers the first one. Your paragraph above also.  
> The current "seventh step series" is leading to the understanding of  
> what is a computation, and a machine, for a mathematician. With or  
> without assuming PM (primitive matter) there is an mathematical notion  
> of computation and of computability.

Ah.  Well, tell me if you still want to make the point about my
'paragraph above', after my response on this.  But on the issue of the
understanding of what is computation, I must concede that I have much
to learn technically - so I will be humble and try to study.

But also - just to dispose once and for all of this particular point -
I want to be sure that you understand that I'm not arguing *for*
eliminative materialism, except as devil's advocate (I'm sure you know
this).  But one aspect of my recent discussions with Peter has been to
bring to a focus the strict consequences of materialism, in precisely
the honest way that you attribute to Dennett.  The trouble is, that
Dennett, having eliminated the mind and hence the notorious 'problem',
still cheerfully carries on deploying the same mind-dependent concepts
as though nothing had happened!  In other words, his position is
inconsistent and incoherent.  It's dualism for free!

So, in this context, let me try to understand your remark: "with or
without assuming PM (primitive matter) there is an mathematical notion
of computation and of computability".  I would say - per Dennett, but
understood *consistently* - that under the assumption that there is
*only* primitive matter (i.e. material monism) - there strictly can be
no appeal to such a notion as computation, because mathematics itself
is eliminable per Qine.  Don't misunderstand me - this is what is
*wrong* with material monism - because to be consistent, one is either
honestly forced to such an eliminativist conclusion (but then you must
deny your own consciousness and all mental concepts), or you tacitly
accept a form of dualism (but again without noticing!)  So I suppose
that when you say "with primitive matter" that you don't mean
"**only** with primitive matter", but rather "with primitive matter +
computation" - which is in effect a dualistic assumption.  Again,
please don't misunderstand me - I regard comp as a coherent *monistic*
approach to both mind and matter that seeks to 'eliminate' neither,
and which brings the mind-body issues into full focus. But the
assumption of PM *in addition* would transform it into a type of
epiphenomenal dualism.

David

> The notion of computation does not rely on anything physical.

OK, with the caveats above.

> I think that what remains unclear in step seven is due to the lack of  
> knowledge of that "purely mathematical" notion of computation. You  
> need it to justify why Universal Machine and Universal Dovetailer"  
> exist and in what sense they are truly universal.

Point taken.  I will try to learn.

David

>
> The notion of physical computation *today* is quantum computation, and  
> this is a priori something else, except it can be shown defining the  
> same class of computable functions.
>
> A big problem for the comp hyp. consists in explaining why apparently  
> everything we can touch and smell is described only by quantum  
> computation. Why in UD* (the infinite execution of the UD, or of any  
> UD) does the quantum computation wins the "measure battle", at least  
> from the first person (plural) points of view. Of course the first  
> person plural indeterminacy explains why, but we have to recover the  
> detail. The apparent "primitive matter" that we recover from comp is a  
> priori "too much powerful, and leads to too much "white rabbits". Only  
> pure mathematical computer science explains why this is not trivial at  
> all.
>
> Bruno
>
> http://iridia.ulb.ac.be/~marchal/
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