Xref: utzoo comp.ai:3038 talk.philosophy.misc:1804 sci.lang:3872 Path: utzoo!attcan!uunet!lll-winken!ames!ncar!boulder!sunybcs!rutgers!elbereth.rutgers.edu!harnad From: harnad@elbereth.rutgers.edu (Stevan Harnad) Newsgroups: comp.ai,talk.philosophy.misc,sci.lang Subject: Re: Categorization Summary: There is absolutely nothing wrong with disjunctive features... Message-ID: Date: 10 Jan 89 05:43:17 GMT References: <681@cogsci.ucsd.EDU> <2959@uhccux.uhcc.hawaii.edu> <684@cogsci.ucsd.EDU> Organization: Rutgers Univ., New Brunswick, N.J. Lines: 158 I'd like to take the discussion of the "classical" [vs. the "quantum"?] view of categories back a few steps to the original question: markh@@csd4.milw.wisc.edu (Mark William Hopkins) of the University of Wisconsin-Milwaukee wrote: " [Lakoff/Rosch's] kind of argument does not rule out the Classical view, " because the predicate: (A and B) or (B and C) or (C and A) *IS* a " necessary and sufficient condition for membership in such a class. " Forgetting about that magical word "or" is Lakoff's mistake. I think this original observation was quite correct, and the rest of the discussion diverged into red herrings and irrelevancies. The supposed argument against the so-called "classical view" is this: The classical view is wrong because (1) people do not use necessary/sufficient conditions to recognize categories and (2) necessary/sufficient conditions for categories do not exist. The evidence for (1) consisted of psychological experiments in which the dependent variable was (a) judgments of category goodness-of-fit, (b) reaction time, and (c) introspections about the features underlying categories. The data suggested that subjects (a') found some members more typical of a category than others, (b') took a longer time to categorize the less typical members, and (c') could not come up with necessary and sufficient conditions for the membership by introspection. The evidence for (2) consisted of (c') (the lack of introspective conditions) plus (d) the fact that some categories indeed lack necessary and sufficient conditions, either because membership is by nature and by definition not all-or-none (as in the category "big" vs "small") or because the boundary between membership and nonmembership is graded, fuzzy, approximate, arbitrary, unknown, or unknowable (as with "living" vs. "nonliving"). What should be apparent from this summary is that none of the conclusions were based on examining categorization itself -- i.e., our ability to categorize an X as an X and a non-X as a non-X for all those X's with which we can demonstrably do this in a reliable, successful, all-or-none fashion. Instead, the conclusions were based on typicality judgments and reaction time, and these were indeed found to be graded, unlike the membership judgments themselves, which were, of course, all-or-none. With experimenters and subjects then all suitably flabbergasted that not only was typicality graded, but no one could think of necessary and sufficient conditions, it was concluded that the underlying representations for categories must prototypes, exemplars, "family resemblances" or what have you, with graded degrees of membership governed by closeness to a prototype rather than all-or-none membership governed by necessary/sufficient conditions. A good enough illustration of this came in this very discussion, where bondc@@iuvax.cs.indiana.edu (Clay M Bond) of Indiana University CSCI, Bloomington wrote: " [My students] began the discussion [of the properties of cups vs " glasses] thinking not only that the "Classical" system was correct, but " also by logical extension, the more defining properties they gave, the " more discrete and well-defined the categories would be. They left the " classroom realizing that the categories were anything but discrete, and " that the more properties they listed, the less discrete the categories " became. rwojcik@@bcsaic.UUCP (Rick Wojcik) added: " [Lakoff's] thinking is strongly influenced by Rosch's psychological " theory of prototypes. Classical categorization does not explain " prototype effects--the impression that some entities belong more " strongly to a category than other entities do... you need some metric " for calculating prototype effects off of such formulas... some " properties are more central than others to a category... it is now " thought biologically possible to grow babies in males. Would " such a male parent be considered the 'mother'? The problem is that this kind of research and this kind of conclusion simply changes the subject: Instead of trying to find (C) the representation that will allow us to perform X/non-X categorization in the myriad cases where we can indeed do it in a reliable, all-or-none fashion, it turns instead to (T) judgments of typicality and to introspections about how we categorize, and then offers T as if it were the mechanism for C, whereas T simply PRESUPPOSES a mechanism for C, without specifying it or even realizing that the question has been begged! Worse yet, a T-mechanism is put forward as a C-mechanism, a job it certainly can't do! To put it simply: The problem of categorization and its underlying representation is the problem of how categorizers like us are able to do what we can do, which includes an enormous core of successful, reliable, correct, all-or-none categorizations as well as a large number of categorizations that are graded to various degrees. I don't categorize a penguin as a bird "to a degree" -- it's a bird, all the way, and I get it right every time. I do find it a less typical bird than a robin. And if I introspect about HOW I manage to categorize it as a bird, I probably can't come up with a set of features that are necessary and sufficient to do so. But SOMETHING up there manages to do it in my head, and it's then my job, not as introspector but as empirical theorist, to try to come up with models for how that can be done. One thing is sure: in all the cases where categorizers are demonstrably able to categorize their input in a reliable, correct all-or-none fashion, there NECESSARILY exists a set of features in the input that is jointly SUFFICIENT to generate the successful performance, and the internal mechanism will certainly detect and represent these, though not necessarily in a consciously accessible way. (As to "necessity": empirical science does not really specialize in this; psychology cannot really hope to discover or stipulate what is necessary for something to BE an X -- just what is sufficient to reliably detect it as an X, when it is indeed detectable.) Now let's move on to the last red herring: Disjunctive features. zhang@@cogsci.ucsd.EDU (Jiajie Zhang) of Institute for Cognitive Science, UC San Diego wrote: " Yes, the predicate (A and B)or(B and C)or(C and A) is a necessary and " sufficient CONDITION of the ABC class you gave, but it is NOT a " necessary and sufficient FEATURE of that class. You confused CONDITION " with FEATURE. Thus the predicate you gave is not relevant to the " problem of categorization... the example you gave is a disjunctive " concept and its existence is a powerful argument used by people against " the classical view, because the second assumption of the classical view " excludes any disjunctive concept in classical categories. Disjunctive " concepts can be accounted for by some alternative views of " categorization such as probabilistic (or prototypic) view and exemplar " view, but these two views are also under criticism (Medin & Smith) What is a feature? Is being curved a feature? What about not being straight? Or not being curved? Or being straight or curved? Would a feature detector that looked for an even number of limbs be detecting a feature? How about an uneven number of limbs? Or a prime or uneven number of limbs? It should be apparent that in any nonarbitrary definition of "feature" (which, by the way, cannot be made independently of an implicit notion of a feature detector) any invariant property of an object, be it monadic, polyadic, relational, negative, conditional, or disjunctive qualifies as a feature. A feature is a detectable state of affairs, describable by a predicate; and some states of affairs are described by disjunctions, negations, conditionals, relational statements (or even quantitative statements of degree -- with or without a reliable all-or-none threshold feature). So I don't know who is the original owner of the "classical view," but whoever excluded disjunctions of features did so completely arbitrarily from the standpoint of any theory of categorization. Yet even prohibiting disjunctive features does not move us toward graded theories (except in cases where category membership is demonstrably graded too, as indicated by graded categorization judgments -- NOT graded typicality judgments). The ongoing rounds of criticism and counter-criticism that have been set off by the Roschian research (to which Zhang alludes at the end of the passage I quoted) are, in my view, simply symptoms of the incoherence of the views that set this whole bandwagon rolling in the first place. (For an alternative approach to categorization, see "Categorical Perception: The Groundwork of Cognition," Cambridge University Press 1987, S. Harnad, Ed., in which I offer a candidate solution to the symbol grounding problem.) -- Stevan Harnad INTERNET: harnad@confidence.princeton.edu harnad@princeton.edu srh@flash.bellcore.com harnad@elbereth.rutgers.edu harnad@princeton.uucp BITNET: harnad@pucc.bitnet CSNET: harnad%princeton.edu@relay.cs.net (609)-921-7771