SUMMARY

From: Higgo James <james.higgo.domain.name.hidden>
Date: Mon, 12 Jul 1999 09:37:10 +0100

I nominate this post by Hal for a slot in the FAQ

> -----Original Message-----
> From: hal.domain.name.hidden [SMTP:hal.domain.name.hidden.org]
> Sent: Saturday, July 10, 1999 7:48 AM
> To: dude.domain.name.hidden; everything-list.domain.name.hidden.com
> Subject: Re: Fwd: COUNTERFACTUALS
>
> Christopher Maloney, <dude.domain.name.hidden>, writes:
> > Marchal wrote:
> > > what Maudlin and me have showed is that
> > >
> > > EITHER the appearance of hardware and consciousness
> > > is explain(able) by the theory of possible softwares (computer
> science,
> > > ...)
> > >
> > > OR the computationalist hypothesis is false.
> >
> > Please explain this, if you have time. I'm sorry if you've already
> > given more detail in other posts, perhaps you could point me to the
> > archives.
> >
> > What exactly is "the computationalist hypothesis"?
> >
> > I gather from the above that "the physical supervenience thesis"
> > has something to do with explaining consciousness as a software
> > program, but I'm confused. I would have *guessed* that that is
> > the "computationalist hypothesis", but you say that those are
> > incompatible, so it can't be.
>
> I got hold of Maudlin's paper yesterday and I will hopefully post more
> on it this weekend.
>
> The computationalist hypothesis is that implementing a certain kind
> of computation is necessary and sufficient for creating consciousness.
> It is an important part of this hypothesis that the implementation must
> include counterfactuals. That is, the implementation must mirror not
> only the behavior of the program given the specific inputs encountered
> on the run, but it must have been such that if other inputs had occured,
> the implementation would still have faithfully followed the rules of
> the program.
>
> This last point is the crucial part for the paradox Maudlin constructs.
>
> The supervenience thesis is that whether consciousness occurs depends
> solely on the physical activity of the system. Two systems with the
> same physical activity will both produce the same consciousness. In
> particular, adding an inert object which does not interact with the
> system should not change its degree of consciousness.
>
> Although these two theses appear compatible, they are contradictory.
> To oversimplify somewhat, the reason is because of the need to implement
> counterfactuals in order to produce consciousness in the computationalist
> hypothesis. Since counterfactuals don't actually occur, this contradicts
> the supervenience hypothesis, which says that consciousness should only
> depend on physical activity, which means it depends on what actually
> happens.
>
> Maudlin constructs an elaborate variant on a Turing machine. It is
> used to replay a previously computed conscious experience, and we want
> to ask whether the replay is conscious. Because it is a replay we
> know exactly what states it will go through, but it is not enough,
> by the computationalist hypothesis, to arrange that the machine
> goes through such a series of states. In addition, the machine has
> to handle counterfactuals - that is, it must be such that if the
> input were different from what was used on the earlier runs, then it
> will still do the right thing.
>
> Maudlin proposes to add to the TM a mechanical clockwork computer which
> handles counterfactuals. This portion of the computer would be activated
> if the input were different from what is expected. It is only used in
> that case, otherwise the main TM just plows through the states that
> were pre-computed from an earlier run.
>
> Now, because this is a replay and all the inputs are the same, the
> clockwork computer will never actually be activated. Nevertheless
> this extra clockwork mechanism MUST be present, according to the
> computationalist hypothesis, otherwise the system does not handle
> counterfactuals and so is not conscious.
>
> Maudlin then proposes to insert a chunk of wood among the gears of
> the clockwork computer such that if it ever tried to start running, it
> would be blocked. This piece of wood does not need to touch anything,
> it just needs to be positioned so that if the gears tried to turn they
> would jam on the wood. (Keep in mind that the gears never actually do
> start to turn.)
>
> By doing so he has changed the machine so that it no longer handles
> counterfactuals properly. Hence by the computationalist hypothesis,
> the machine will no longer be conscious. However, his inert chunk of
> wood makes no actual difference in the activity of the machine. Hence
> by the supervenience hypothesis, the machine continues to be conscious.
>
> The two theses give opposite predictions and hence are incompatible.
>
> This short description does not really do Maudlin's 20-page argument
> justice but hopefully explains the basic idea.
>
> Hal
Received on Mon Jul 12 1999 - 01:40:02 PDT