Path: utzoo!mnetor!tmsoft!torsqnt!jarvis.csri.toronto.edu!rutgers!usc!samsung!shadooby!sharkey!itivax!dhw
From: dhw@itivax.iti.org (David H. West)
Newsgroups: comp.ai
Subject: Re: What is a Symbol System?
Keywords: computation, symbol manipulation, syntax, formality
Message-ID: <4481@itivax.iti.org>
Date: 24 Nov 89 16:00:05 GMT
References: <11640@phoenix.Princeton.EDU> <17189@netnews.upenn.edu> <11657@phoenix.Princeton.EDU> <1656@aipna.ed.ac.uk>
Reply-To: dhw@itivax.UUCP (David H. West)
Organization: Industrial Technology Institute
Lines: 92

In article <1656@aipna.ed.ac.uk> cam@aipna.ed.ac.uk (Chris Malcolm) writes:
]In article <11657@phoenix.Princeton.EDU> harnad@phoenix.Princeton.EDU (S. R. Harnad) writes:
]
]>Here is an easy example. I think it contains all the essentials:
]>We have two Rube Goldberg devices, both beginning with a string
]>you pull, and both ending with a hammer that smashes a piece of
]>china. Whenever you pull the string, the china gets smashed by the
]>hammer in both systems. The question is: Given that they can both be
]>described as conforming to the rule "If the string is pulled, smash the
]>china," is this rule explicitly represented in both systems?

This is not an empirical question, but a question about how we wish
to use the words "described", "explicitly" and "rule".

]In your original posting you (Stevan Harnad) said:
]
]    So the mere fact that a behavior is "interpretable" as ruleful
]    does not mean that it is really governed by a symbolic rule.

There IS no "really": we can interpret our "observations" as we
wish, and take the consequences of our choice.

]    Semantic interpretability must be coupled with explicit
]    representation (2), syntactic manipulability (4), and
]    systematicity (8) in order to be symbolic.
]	
]There is a can of worms luring under that little word "coupled"!  What I
]take it to mean is that this symbolic rule must cause the behaviour
]which we interpret as being governed by the rule we interpret the
]symbolic rule as meaning. 

Rather: if WE are to call the system "symbolic", the meaning WE
ascribe to the symbols should be consistent with (OUR interpretation
of) the behavior we wish to regard as being caused by the rule.

]                          Unravelled, that may seem stupendously
]tautologous, but meditation on the problems of symbol grounding can
]induce profound uncertainty about the status of supposedly rule-governed
]AI systems. One source of difficulty is the difference between the
]meaning of the symbolic rule to the system 

We can have no epistemological access to "the meaning of the
symbolic rule to the system" except insofar as we construct for
ourselves a consistent model containing something that we interpret
as such a meaning.   Symbol-grounding happens entirely within our
mental models.  Additionally, many of us believe that the world is
not conducive to the replication of systems that react in certain
ways (e.g. an object labelled "thermostat" which turns a heater ON
when the temperature is ABOVE a threshold is unlikely to attract
repeat orders), and this could be regarded as a mechanism for
ensuring symbol-function consistency, but the latter is still all
in our interpretation.

]Brian Smith's Knowledge Representation Hypothesis contains a nice
]expression of this problem of "coupling" interpretation and causal
]effect, in clauses a) and b) below.
]
]    Any mechanically embodied intelligent process will be be
]    comprised of structural ingredients that a) we as external
]    observers naturally take to represent a propositional account of
]    the knowledge that the overall process exhibits, and b)
]    independent of such external semantical attribution, play a
]    formal but causal and essential role in engendering the
]    behaviour that manifests that knowledge.
	
I agree.

]It is not at all clear to me that finding a piece of source code in the
]controlling computer which reads IF STRING_PULLED THEN DROP_HAMMER is
]not just a conjuring trick where I am misled into equating the English
]language meaning of the rule with its function within the computer
]system [Drew McDermott, Artificial Intelligence meets Natural Stupidity

As McDermott points out, the behavior of such a system is unaffected
if all the identifiers are systematically replaced by gensyms 
(IF G000237 THEN (SETQ G93753 T)), which causes the apparently
"natural" interpretation to vanish.

]Why should we bother with being able to interpret the system's "rule" as
]a rule meaningful to us? 

It may just be the way we are.

]But how
]can we do this weakening, without letting in such disturbingly ambiguous
]exemplars as neural nets?

If we are "disturbed", it's a sign of internal inconsistency in our
construction of a world-view.  People used to be disturbed by the
idea of light being both wave and particle.  Now we're not.

-David West            dhw@itivax.iti.org