Path: utzoo!mnetor!tmsoft!torsqnt!jarvis.csri.toronto.edu!rutgers!ucsd!usc!wuarchive!udel!princeton!phoenix!harnad From: harnad@phoenix.Princeton.EDU (S. R. Harnad) Newsgroups: comp.ai Subject: Re: What is a Symbol System? Summary: Define Symbol Systems first, then worry about their limitations. Keywords: computation, symbol manipulation, syntax, formality Message-ID: <11711@phoenix.Princeton.EDU> Date: 24 Nov 89 18:46:57 GMT References: <11640@phoenix.Princeton.EDU> <17189@netnews.upenn.edu> <1656@aipna.ed.ac.uk> Organization: Princeton University, NJ Lines: 100 Chris Malcolm cam@aipna.ed.ac.uk of Dept of AI, Edinburgh University, UK, wrote: > What I take [you] to mean is that [the] symbolic rule must cause the > behaviour which we interpret as being governed by the rule we interpret > the symbolic rule as meaning... 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 (as > defined by its use of the rule) and the meaning we are tempted to > ascribe to it because we recognise the meaning of the variable names, > the logical structure, etc. I endorse this kind of scepticism -- which amounts to recognizing the symbol grounding problem -- but it is getting ahead of the game. My definition was only intended to define "symbol system," not to capture cognition or meaning. You are also using "behaviour" equivocally: It can mean the operations of the system on the world or the operations of the system on its symbol tokens. My definition of symbol system draws only on the latter (i.e., syntax); the former is the grounding problem. It is important to note that the only thing my definition requires is that symbols and symbol manipulations be AMENABLE to a systematic semantic interpretation. It is premature (and as I said, anaother problem altogether) to require that the interpretation be grounded in the system and its relation to the world, rather than just mediated by our own minds, in the way we interpret the symbols in a book. All we are trying to do is define "symbol system" here; until we first commit ourselves on the question of what is and is not one, we cannot start to speak coherently about what its shortcomings might be! (By the way, "meaning to us" is unproblematic, whereas "meaning to the system" is highly contentious, and again a manifestation of the symbol grounding problem, which is certainly no definitional matter!) > 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... In simple cases with a few rules and > behaviour which can easily be exhaustively itemised we can satisfy > ourselves that our interpretation of the rule does indeed equate with > its causal role in the system. Where there are many rules... The best > we can say is that our interpretation is _similar_ to the function of > the rule in the system. How reliably can we make this judgment of > similarity? And how close must be the similarity to justify our > labelling an example as an instance of behaviour governed by an > explicit rule? Again, you're letting your skepticism get ahead of you. First let's agree on whether something's a symbol system at all, then let's worry about whether or not its "meanings" are intrinsic. Systematic interpretability is largely a formal matter; intrinsic meaning is not. It is not a "conjuring trick" to claim that Peano's system can be systematically interpreted as meaning what WE mean by, say, numbers and addition. It's another question altogether whether the system ITSELF "means" numbers, addition, or anything at all: Do you see the distinctions. (No one, has actually proposed the Peano system as a model of arithmetic understanding, of course; but in claiming, with confidence, that it is amenable to being systematically interpreted as what we mean by arithmetic, we are not using any "conjuring tricks" either. It is important to keep this distinction in mind. Number theorists need not be confused with mind-modelers.) But, as long as you ask, the criterion for "similarity" that I have argued for in my own writings is the Total Turing Test (TTT), which, unlike the conventional Turing Test (TT) (which is equivocal in calling only for symbols in and symbols out) calls for our full robotic capacity in the world. A system that can only pass the TT may have a symbol grounding problem, but a system that passes the TTT (for a lifetime) is grounded in the world, and although it is not GUARANTEED to have subjective meaning (because of the other minds problem), it IS guaranteed to have intrinsic meaning. (The "Total" is also intended to rule out spurious extrapolations from toy systems: These may be symbol systems, and even -- if robotic -- grounded ones, but, because they fail the TTT, there are still strong grounds for skepticism that they are sufficiently similar us in the relevant respects. Here I do agree that what is involved is, if not "conjuring," then certainly wild and unwarranted extrapolation to a hypothetical "scaling up," one that, in reality, would never be able to reach the TTT by simply doing "more of the same.") > Why should we bother with being able to interpret the system's "rule" as > a rule meaningful to us? Because that's the part of how you tell whether you're even dealing with a formal symbol system in the first place (on my definition). Stevan Harnad ------------------------------------------------------------------ -- 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