Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!rutgers!cmcl2!yale!cs.yale.edu!mcdermott-drew
From: mcdermott-drew@CS.YALE.EDU (Drew McDermott)
Newsgroups: comp.ai
Subject: Re: What is a Symbol System?
Keywords: symbol manipulation, syntax, formality, semantics
Message-ID: <6921@cs.yale.edu>
Date: 29 Nov 89 03:05:17 GMT
References: <11640@phoenix.Princeton.EDU> <6170@cs.yale.edu> <11655@phoenix.Princeton.EDU>
Sender: news@cs.yale.edu
Reply-To: mcdermott-drew@CS.YALE.EDU (Drew McDermott)
Organization: Yale University Computer Science Dept, New Haven CT  06520-2158
Lines: 71

In article <11655@phoenix.Princeton.EDU> harnad@phoenix.Princeton.EDU (S. R. Harnad) writes:
>
>
>mcdermott-drew@CS.YALE.EDU (Drew McDermott) of
>Yale University Computer Science Dept asked:
>
>> Why is it necessary that a symbol system have a semantics in order to
>> be a symbol system? I mean, you can define it any way you like, but
>> then most AI programs wouldn't be symbol systems in your sense.
>> 
>I'd rather not define it any way I like. I'd rather pin people down on
>a definition that won't keep slipping away, reducing all disagrements
>about what symbol systems can and can't do to mere matters of
>interpretation.
> ...

Which "people" need to be pinned down?  Fodor, I guess, who has a strong
hypothesis about a Representational Theory of Meaning.

But suppose someone believes "It's all algorithms," and not much more?
He's willing to believe that intelligence involves an FFT here, some
inverse dynamics there, a few mental models, maybe some neural nets,
perhaps a theorem prover or two,....  His view is not completely vacuous
(Searle thinks it's even false).  It might be a trifle eclectic for some
philosophers, but so what?

I realize that there is an issue about what symbol systems "can and
can't do."  It might turn out that computation is just a ridiculous
model for what goes on in the brain.  All the AI types and cognitive
psychologists could then find something else to do.  But it's simply
not possible that it could be revealed that there was a task X such
that symbol systems cannot do X and some other computational system
can.  That's because I and all the other computationalists would just
incorporate that new sort of system in our universe of possible
models.  We wouldn't even notice that it hadn't been incorporated
already.  In spite of philosophers' ardent hopes, there simply is no
natural category of Physical Symbol Systems separate from
Computational Systems in General.

>So the only thing at issue is whether a symbol system is required to be
>semantically interpretable. Are you really saying that most AI programs
>are not? I.e., that if asked what this or that piece of code means
>or does, the programmer would reply: "Beats me! It's just crunching
>a bunch of meaningless and uninterpretable symbols."
>
> ...
>Stevan Harnad  Department of Psychology  Princeton University
>harnad@confidence.princeton.edu       srh@flash.bellcore.com
>harnad@elbereth.rutgers.edu    harnad@pucc.bitnet    (609)-921-7771

Well, of course, no one's going say, "My program is crunching meaningless
symbols."  The word "meaningless" has all these negative connotations;
it sounds like it's next to "worthlessness," "pointlessness."  So
everyone will cheerfully claim that their symbols are "meaningful."
But if you press them on exactly what they're committing to, you're
usually going to start hearing about "procedural semantics" or
"holistic semantics" or some such twiddle.

The fact is that most symbols are conceived of as calculational
devices rather than denotational devices; their function is to compute
rather than to mean.  Try asking a rug merchant what the meaning is of
the position of the third bead on the second wire of his abacus.  If
he thinks hard, he might come up with something like "It denotes the
third ten in the count of shekels paid for these rugs."  But chances
are it never crossed his mind that the bead position required a
denotation.  After all, it's part of a formal system.  The meanings of
the expressions of such a system can't enter into its functioning.
Why then is it so all-fired important that every expression have a
meaning?

                                             -- Drew McDermott


Brought to you by Super Global Mega Corp .com