🚀 go-pugleaf

In article <1037@ra.stsci.edu> bsimon@stsci.EDU (Bernie Simon) writes:

>I would like to make a few point that seem clear to me, but apparently
>aren't clear to others in this discussion.

Hmmm, do I take it from the references line that you mean me?

>1) All physical objects are not machines. 
>2) Not all machines are computers.
>3) There are some activities which can be performed by physical objects
>and machines which cannot be performed by computers.

1) Arguable but not relevant.
2) Of course.
3) Of course.

>Birds can fly and airplanes can fly, but computers cannot fly. [...]
>4) The simulation of a physical activity by a computer cannot be
>identified with the physical activity. A computer running a flight
>simulation program is not flying.
>5) Hence, while it may be possible to build a machine that thinks, it
>does not follow that it will be possible to build a computer that
>thinks, as not all physical activities can be performed by computers.

If you recall, the *premise* of the current discussion was that thinking is
thinking in virtue of its abstract causal structure, and not in virtue of
physical details of implementation.  If you want to argue with this premise
 -- functionalism -- then fine.  The point was not to defend it, but to defend
a view of the relation between computation and cognition which is less
simple-minded than "the mind is a computer".

Of course, I also believe that functionalism is true.  The functionalist
believes that thinking is fundamentally different to flying (and heating,
swimming, and nose-blowing).  The essence of flying certainly *cannot*
be captured in an abstract causal structure.  This is because there are
substantive *physical* criteria for flying.  An object, *by definition*,
is not flying unless it is (very roughly) engaged in ongoing motion without
any connection to the ground.  Nothing abstract about this -- it's a solid,
physical criterion. If you capture the causal patterns without the correct
physical realization, then it's not flying, period.  Similarly for
nose-blowing and the rest. 

Thinking, on the other hand, has no such solid criteria in its definition.
The only definitive criterion for thought is "having such and such a subjective
experience" -- which is far away from physical details (and a criterion which
is understood notoriously badly).  Of course, this doesn't *prove* that
thinking is not nevertheless inseparable from physical details -- a correct
theory of mind *might* just require that for these experiences, you can't
get away with anything but pointy-headed neurons.  But at the very least,
physical details are out of the *definition*, and there is thus a
principled difference between thinking and flying.  Which makes the jump to
functionalism much more plausible.  Maybe "thinking" is more like "adding"
than like "flying".

Most arguments against functionalism are in terms of "funny instantiations" --
as in "but *this* has the right causal dynamics, and surely *this* doesn't
think".  Generally Chinese objects seem to be favoured for these arguments --
whether Rooms, Gyms or Nations.  Some people find these intuitively compelling.
As for me, I find the arguments sufficiently unconvincing that my "faith" is
not only affirmed but strengthened.

>6) While there are good reasons to believe that thinking is a physical
>activity, there are no good reasons for believing that thinking is the
>execution of a computer program. Nothing revealed either through
>introspection or the examination of the anatomy of the brain leads to
>the conclusion that the brain is operating as a computer. If someone
>claims that it is, the burden of proof is on that person to justify that
>claim. Such proof must be base on analysis of the brain's structure and
>not on logical, mathematical, or philosophical grounds. Since even the
>physical basis of memory is poorly understood at present, any claim that
>the brain is a computer is at best an unproven hypothesis.

I agree.  Did you read my first note?  The whole point is that you can accept
the computational metaphor for mind *without* believing somewhat extreme
statements like "the brain is a computer", "the mind is a program", "cognition
is just symbol-manipulation" and so on.  The role of computer programs is
that they are very useful formal specifications of causal dynamics (which
happen to use symbols as an intermediate device).  Implementations of
computer programs, on the other hand, possess *physically* the given causal
dynamics.  So if you accept (1) functionalism, and (2) that computer programs
can capture any causal dynamics, then you accept that implementations of
the right computer programs think.

--
Dave Chalmers     (dave@cogsci.indiana.edu)      
Concepts and Cognition, Indiana University.
"It is not the least charm of a theory that it is refutable"