From: holmes@opal.idbsu.edu (Randall Holmes)
Subject: Re: Dualism
Organization: Boise State University
Date: Tue, 13 Oct 1992 19:12:35 GMT

In article <7672@skye.ed.ac.uk> jeff@aiai.ed.ac.uk (Jeff Dalton) writes:
>In article <1992Sep22.175911.1375@guinness.idbsu.edu> holmes@opal.idbsu.edu (Randall Holmes) writes:
>>In article <BuypA4.K9p@usenet.ucs.indiana.edu> chalmers@bronze.ucs.indiana.edu (David Chalmers) writes:
>>[...]
>>>So, in this case, I'm asserting the logical possibility of a zombie
>>>replica of me, which certainly *seems* coherent.  The burden on
>>>those who dispute this is to provide the slightest idea of
>>>how it might entail a contradiction, or equivalently, how the
>>>physical facts might entail the facts about consciousness.  This
>>>is what they've manifestly failed to do.
>>
>>It entails a contradiction if the facts in the two cases are _the same
>>facts_; you can only assume that it is _possible_ that they are
>>different if they are in fact different. 
>
>When you say it this way ("possible that they are different"), 
>you seem to be talking about whether it is possible in the actual
>world, meaning : it is possible that it is the case in the actual
>world?  When we talk like this we usually mean something like
>"given what we know, it it possible that...".  For instance,
>
>   Is it possible that the man seen outside the shop and the
>   man who killed the shopkeeper are the different?
>
>Once we find out they're the same, we stop think it's possible
>that they're different.  So possibility comes in as a sort of
>epistemic possibility.
>
>But the issue of logical possibility is quite different.  Even 
>if in this (actual) world the man seen outside the shop and the
>man who killed the shopkeeper are the same, there are other
>logically possible worlds in which they are not the same.
>For instance, the killer might go out the back and not be seen
>while someone else walked out the front.  This is the sort of
>possible we have in mind when we ask "Could Ford have beaten
>Carter?" and not when we ask "Could Ford be someone other
>than himself?"
>
>-- jd

Chalmers is working in a scheme of modal logic in which two things
which are possibly different are necessarily different.  The fallacy
in his argument is that he _cannot_ prove that qualia are different
from certain physical events by claiming that there is a possible
world in which they are different; he cannot build that possible world
without covertly assuming the difference he is trying to prove.  If
consciousness = relevant physical events in this world, then the
equation holds in all possible worlds, in the scheme of modal logic
which Chalmers is using.  The point is that "it seems possible for
there to be a zombie replica of myself" does not use the word
"possible" in the techincal sense required to say that there is a
possible world in which this is the case.  It means something like
"imaginable", and the logic of "imaginable" is a little different.  I
can imagine worlds with vital forces, phlogiston, caloric, and
non-physical qualia just as well as Mr. Chalmers.  Moreover, there are
possible worlds in the technical sense in which it would make sense to
talk about these things.  But the "non-physical qualia" in such a
possible world would not correspond to the actual (physical) qualia in
this world if qualia = physical events holds, and such an argument
cannot prove the impossibility of the equation.


-- 
The opinions expressed		|     --Sincerely,
above are not the "official"	|     M. Randall Holmes
opinions of any person		|     Math. Dept., Boise State Univ.
or institution.			|     holmes@opal.idbsu.edu
Newsgroups: sci.philosophy.tech