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In article <BuHEHG.9Cu@usenet.ucs.indiana.edu> chalmers@bronze.ucs.indiana.edu (David Chalmers) writes:

>Well, many aspects of mentality are almost certainly causally
>efficacious: things like learning, memory, belief, desire, and
>so on.  That sort of thing seems to logically supervene on the
>physical facts ...
>
>The problem of epiphenomenalism only really arises in a strong
>form for the phenomenal aspects of mind, i.e. conscious experiences,
>or "qualia" as philosophers call them.  These aren't characterized
>functionally, and don't seem to logically supervene on the physical.

Let me see if I've got this right.  Many of us have speculated at some time
or another whether or not the color green "looks the same" to other people
as it does to us.  Maybe other people, when they see a red cape, see what I
see when I see green, but call it red.

Consider the Turing test.  Suppose a machine passes the Turing test.  Is
it thereby conscious?  In principle it seems that a very simple but
extremely detailed computer program---namely, one that has a vast number
of "if-then" statements covering every possible stimulus that it might
encounter---could pass the Turing test, but would leave many uncertain
about calling it "conscious."

The above are the intuitions underlying Dave Chalmers' argument, I think.
A complete catalogue of physical facts about vision might still leave us
wondering whether or not other people's visual experiences are the "same"
as ours.  Similarly, even if no human being can devise a test that will
distinguish between Dave Chalmers and the if-then monster, and even if we
have a complete listing of the if-then monster, we might still be unsure
about whether the if-then monster is conscious, even though it assures us
that it is.

	Us: Are you conscious?
   Monster: [encountering "IF STIMULUS('ARE YOU CONSCIOUS?') THEN
              RESPONSE('OF COURSE---WHAT DO YOU THINK?')"]  Of course---
              what do you think?

In response to this one can simply dismiss talk of "consciousness" and
"visual experience" as vague terms; questions like "Is the machine
conscious?" or "Are other people's visual experiences the same as mine?"
don't make precise sense until "consciousness" and "visual experience" are
defined behavioristically or in terms of physical facts.  And of course
once we have such a definition we can answer the question by referring to
our catalogue of physical facts.  This is the physicalist approach.

One might object that our experiences of redness, solidity, and other
conscious experiences are about as basic as we can get, and arguably even
the term "physical facts" is ultimately defined in terms of such
fundamental experiences.  To define these experiences in terms of physical
facts would be circular.  At least it requires a strong argument to say
that the experience of redness is really nothing more than a bunch of
exceedingly complicated and intricate physical facts.

Do I have the issue straight?
-- 
Tim Chow     tycchow@math.mit.edu
Where a calculator on the ENIAC is equipped with 18,000 vacuum tubes and weighs
30 tons, computers in the future may have only 1,000 vacuum tubes and weigh
only 1 1/2 tons.                               ---Popular Mechanics, March 1949