Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rutgers!princeton!mind!harnad From: harnad@mind.UUCP (Stevan Harnad) Newsgroups: comp.cog-eng,comp.ai Subject: Re: The symbol grounding problem: Against Rosch & Wittgenstein Message-ID: <955@mind.UUCP> Date: Thu, 2-Jul-87 00:36:37 EDT Article-I.D.: mind.955 Posted: Thu Jul 2 00:36:37 1987 Date-Received: Fri, 3-Jul-87 04:44:04 EDT References: <.... <6174@diamond.BBN.COM> <917@mind.UUCP> <14269@teknowledge-vaxc.ARPA> Organization: Cognitive Science, Princeton University Lines: 80 Summary: Wittgenstein did not have to worry about modeling categorization Xref: mnetor comp.cog-eng:172 comp.ai:602 dgordon@teknowledge-vaxc.ARPA (Dan Gordon) of Teknowledge, Inc., Palo Alto CA writes: > finding an objective basis for a performance and getting a device to > do it given the same inputs are two different things. We may be able > to find an objective basis for a performance but be unable...to get a > device to exhibit the same performance. And, I suppose, the converse > is true: we may be able to get a device to mimic a performance without > understanding the objective basis for the model I agree with part of this. J.J. Gibson argued that the objective basis of much of our sensorimotor performance is in stimulus invariants, but this does not explain how we get a device (like ourselves) to find and use those invariants and thereby generate the performance. I also agree that a device (e.g., a connectionist network) may generate a performance without our understanding quite how it does it (apart from the general statistical algorithm it's using, in the case of nets). But the point I am making is neither of these. It concerns whether performance (correct all-or-none categorization) can be generated without an objective basis (in the form of "defining" features) (a) existing and (b) being used by any device that successfully generates the performance. Whether or not we know know what the objective basis is and how it's used is another matter. > There may in fact be categorization performances that a) do not use > a set of underlying features; b) have an objective basis which is not > feature-driven; and c) can only be simulated (in the strong sense) by > a device which likewise does not use features. This is one of the > central prongs of Wittgenstein's attack on the positivist approach to > language, and although I am not completely convinced by his criticisms, > I haven't run across any very convincing rejoinder. Let's say I'm trying to provide the requisite rejoinder (in the special case of all-or-none categorization, which is not unrelated to the problems of language: naming and description). Wittgenstein's arguments were not governed by a thoroughly modern constraint that has arisen from the possibility of computer simulation and cognitive modeling. He was introspecting on what the features defining, say, "games" might be, and he failed to find a necessary and sufficient set, so he said there wasn't one. If he had instead asked: "How, in principle, could a device categorize "games" and "nongames" successfully in every instance?" he would have had to conclude that the inputs must provide an objective basis which the device must find and use. Whether or not the device can introspect and report what the objective basis is is another matter. Another red herring in Wittegenstein's "family resemblance" metaphor was the issue of negative and disjunctive features. Not-F is a perfectly good feature. So is Not-F & Not-G. Which quite naturally yields the disjunctive feature F-or-G. None of this is tautologous. It just shows up a certain arbitrary myopia there has been about what a "feature" is. There's absolutely no reason to restrict "features" to monadic, conjunctive features that subjects can report by introspection. The problem in principle is whether there are any logical (and nonmagical) alternatives to a feature-set sufficient to sort the confusable alternatives correctly. I would argue that -- apart from contrived, gerrymandered cases that no one would want to argue formed the real basis of our ability to categorize -- there are none. Finally, in the special case of categorization, the criterion of "defining" features also turns out to be a red herring. According to my own model, categorization is always provisional and context-dependent (it depends on what's needed to successfully sort the confusable alternatives sampled to date). Hence an exhaustive "definition," good till doomsday and formulated from the God's-eye viewpoint is not at issue, only an approximation that works now, and can be revised and tightened if the context is ever widened by further confusable alternatives that the current feature set would not be able to sort correctly. The conflation of (1) features sufficient to generate the current provisional (but successful) approximation and (2) some nebulous "eternal," ontologically exact "defining" set (which I agree does not exist, and may not even make sense, since categorization is always a relative, "compared-to-what?" matter) has led to a multitude of spurious misunderstandings -- foremost among them being the misconception that our categories are all graded or fuzzy. -- Stevan Harnad (609) - 921 7771 {bellcore, psuvax1, seismo, rutgers, packard} !princeton!mind!harnad harnad%mind@princeton.csnet harnad@mind.Pobjectivjohch