Re: computationalism and supervenience

From: Bruno Marchal <>
Date: Wed, 30 Aug 2006 12:02:03 +0200

Le 29-août-06, à 13:14, Stathis Papaioannou a écrit :

> I'm not necessarily talking about every possible computation being
> implemented by
> every physical system, just (at least) the subset of finite
> computations implemented by
> a physical computer or brain. I think this is another way of saying
> that a recording, or
> a single trace of a computation branching in the multiverse, can be
> conscious. To prevent
> a recording being consious yoiu can insist on counterfactual
> behaviour, but that seems an
> ad hoc requirement introduced simply to prevent the "trivial" case of
> a recording or any
> physical system implementing a computation.

I think Maudlin's reasoning (better than the movie graph actually)
shows exactly that. What Maudlin shows is that you can have some
"recording" of a computation, and thus it does not handle the
counterfactuals, but which can be made handling correctly the
counterfactuals by adding pieces of inert matter, having no
comp-genuine physical activity at all.
So the counterfactual correctness demand can be provided without adding
*any* physical activity.
So, for a physicalist, counterfactual should be a red herring 'even
with the quantum MWI (but as Russell points out, this is slightly more
difficult to show).
For a computationalist, this means the entire "physical activity" is a
red herring. The only counterfactuals which play a role are those
corresponding to the mathematical structure of the computations. The
physical emerges from the computational structure, which is entirely
define by the number theoretical relation which are true independently
of any physical considerations.

More technical remark: Counterfactuality is a very difficult notion. It
is certainly one of the philosophical notion where logic (as a field of
math) can help. The best work has been done by logician like David
Lewis (notably in his book "counterfactuals") and Stalnaker. Now the
quantum logician Hardegree has shown that, at least formally, Quantum
Logic (QL) can be seen as a logic of counterfactuals. QL gives a
genuine notion of proximity among "worlds" capable of providing truth
value for counterfactual statements. This shows that the movie graph or
OLYMPIA can be used for providing a shortcut between comp and the
quantum. Alas, the movie graph and/or Olympia thought experiment is far
subtler than the UDA (at least the seven first steps), and I am not
following that road. The counterfactual logic and QL necessary for a
minimal notion of comp-causality is provided by the G and G* variants
Bp & Dp (corresponding to the "intelligible matter" secondary hypostase
in Plotinus, and Bp & Dp & p (corresponding to sensible matter) in the
lobian interview.


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Received on Wed Aug 30 2006 - 06:03:59 PDT

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