David Nyman wrote:
> 2009/9/2 Brent Meeker <meeke...@dslextreme.com>
>
>   
>>> I'm afraid that still doesn't work.  I realise it's counter intuitive,
>>> but this is the point - to recalibrate the intuitions.  'Standard' CTM
>>> postulates that the mind is a computation implemented by the brain,
>>> and hence in principle implementable by any physical process capable
>>> of instantiating the equivalent computation.  Bruno's 'version' starts
>>> with this postulate and then shows that the first part of the
>>> hypothesis - i.e. that the mind is computational - is incompatible
>>> with the second part - i.e. that it is implemented by some
>>> specifically distinguishable non-computational process.
>>>       
>> That's the step I don't grasp.  I see that the MGA makes it plausible
>> that the mind could be a computation divorced from all physical
>> processes - but not that it must be.  Maybe you can explain it.
>>     
>
> Well, I'll recapitulate what insight I possess.
>
> As I see it, both MGA and Olympia are intended to show how
> postulating, on the basis of PM, that invariant mental states
> supervene qua computatio, as Bruno would say, on non-invariant
> physical causes is flatly incoherent - i.e. it leads to absurd
> consequences.  
But the physical implementation (cause?) is invariant in it's functional 
relations.  That's why two physical implementations which are different 
at some lower level can be said to implement the same computation at a 
higher level.  I see nothing incoherent is saying that two physically 
different computers perform the same computation.  So if mental states 
are certain kinds of computations (either physically realized or in 
Platonia) they can be realized on different, i.e. non-invariant physical 
processes.  What's incoherent about that?

And that's where my idea that the context/environment is essential.  It 
defines the level at which functions must be the same; in other words 
when we say yes to the doctor we are assuming that he will replace our 
brain so that it has the same input/ouput at the level of our afferent 
and efferent nerves and hormones (roughly speaking).  Then we would 
continue to exist in and experience this world.  This is why we would 
hesitate to say yes to the doctor if he proposed to also simulate the 
rest of world with which we interact, e.g. in a rock, because it would 
mean our consciousness would be in a different world - not this one, 
which due to it's much greater complexity would not be emulable.

> This, as you know, has always been the brunt of my own
> argument: i.e. that *any* plausible ascription of 'state' under PM
> must be justified physically and hence the postulates are prima facie
> self-contradictory.  

I have no idea what that means.  What postulates?  What does it mean for 
a state to be ascribed and for that to justified physically?

> The whole notion of computational invariance in a
> physical, as opposed to mathematical, sense seems to me a confusion
> arising from the failure to distinguish outcomes from processes.
>   
That's certainly a confusion - but not one I've heard on this list.  I


> Anyway, MGA/Olympia proceed by reducing the foregoing to a
> demonstration that a formally invariant computation putatively
> implementing a correspondingly invariant mental state can ex hypothesi
> be shown to supervene on either minimal or zero physical activity.
>   
But only by isolating a bit of computation from the rest of universe.  
And it doesn't show that a computation supervenes on zero physical 
activity.  And even if it did show that, it would not follow that mental 
computation *does* supervene on computation realized in Platonia  with 
zero physical activity.


> This is an absurd conclusion, so the hypothesis that motivates it -
> i.e. CTM+PM - is thus shown to be contradictory and must be abandoned,
> not merely in this case, but in general: i.e. the exception has broken
> the rule.  This is forced unless you can show where the logic goes
> wrong.
>   
No, even if the conclusion is wrong that only shows that *some* step in 
the argument is wrong NOT that the conjunction of the computationalist 
theory of mind and primary matter is self contradictory.  I don't even 
see where the argument uses PM to reach its conclusion.  Maybe CTM+UD is 
a simpler explanation of the world, a return to Platonic idealism, but I 
don't see that its contrary is contrdictory.

Brent

> Given the foregoing, the contradiction can in principle be resolved by
> abandoning one or the other component of the conjunction.  That is, we
> can retain PM, but with the proviso that mind can no longer be
> attached to matter qua computatio.  Alternatively, we can retain CTM,
> explicitly extended to a comp theory of mind-body, but with the
> realisation that it can't be justified as such qua PM.  Your preferred
> choice is not forced by the argument, but the choice itself is forced
> else the contradiction can't be resolved.  That's it.
>
> Actually, because of my prior queasiness about CTM+PM, I don't find
> this dichotomy so very surprising, because CTM+PM always struck me as
> an unjustifiable attempt to conjure a ghost from the machine to stand
> in for mind.  It only seems odd because the coherence of the a priori
> assumption of CTM in the face of PM is not usually challenged and
> destroyed in so explicit a manner.  Nonetheless, if it's a ghost we're
> after, we can still snare one by abandoning any appeal to the machine
> (the physical one that is).  And in so doing, we can if we like, and
> in denial of Occam, go on imagining a primitively physical machine out
> there somewhere, but since ghosts and machines can't interact, this
> turns out to be the sort of difference that makes no difference.
>
> David
>
>   


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