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From: harnad@phoenix.Princeton.EDU (S. R. Harnad)
Newsgroups: comp.ai
Subject: Re: What is a Symbol System?
Summary: Who deals in uninterpretable symbols?
Keywords: symbol manipulation, syntax, formality, semantics
Message-ID: <11655@phoenix.Princeton.EDU>
Date: 20 Nov 89 22:07:02 GMT
References: <11640@phoenix.Princeton.EDU> <6170@cs.yale.edu>
Organization: Princeton University, NJ
Lines: 40



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.
> 
> Perhaps you have in mind that a system couldn't really think, or
> couldn't really refer to the outside world without all of its symbols
> being part of some seamless Tarskian framework...  I think you have to
> buy several extra premises about the potency of knowledge
> representation to believe that formal semantics is that crucial.

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.

I gave semantic interpretability as a criterion, because it really
seems to be one of the properties people have in mind when they
single out symbol systems. However, semantic interpretability is
not the same as having an intrinsic semantics, in the sense that
mental processes do. But I made no reference to anything mental
("thinking," reference," "knowledge") in the definition.

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."

No, I still think an obvious sine qua non of both the formal symbol
systems of mathematics and the computer programs of computer science
and AI is that they ARE semantically interpretable.
-- 
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