Xref: utzoo comp.ai:3086 talk.philosophy.misc:1830 sci.lang:3932 Path: utzoo!attcan!uunet!lll-winken!ames!xanth!nic.MR.NET!csd4.milw.wisc.edu!leah!itsgw!nyser!njin!aramis.rutgers.edu!elbereth.rutgers.edu!harnad From: harnad@elbereth.rutgers.edu (Stevan Harnad) Newsgroups: comp.ai,talk.philosophy.misc,sci.lang Subject: Re: Categorization Summary: The non-arbitrariness of categories with objective consequences Message-ID: Date: 14 Jan 89 06:13:05 GMT References: <681@cogsci.ucsd.EDU> <2959@uhccux.uhcc.hawaii.edu> <976@husc6.harvard.edu> Organization: Rutgers Univ., New Brunswick, N.J. Lines: 119 reiter@harvard.UUCP (Ehud Reiter) Aiken Computation Lab Harvard, Cambridge, MA wrote: " Biological categories are a lot more arbitrary than many people seem to " realize... there is no direct experimental test that determines whether " or not a group of individuals belongs to the same genera, class, or " whatever. At least in this sense, higher classifications (e.g. "bird", " "penguin", "mammal", etc) are human inventions, not distinctions that " are mandated by nature. To quote Mayr, pg 98 " " "...the major function of a classification [is] to be useful. " A classification is a communication system, and the best one is " that which combines greatest information content with greatest " ease of information retrieval." "Information content" depends on resolving uncertainty. Objective uncertainty is a function of objective consequences: It matters whether this is a "mushroom" or a "toadstool," because if I miscategorize, I may die. To the extent that categorization is guided by objective consequences, it is nonarbitrary. Subjective uncertainty is another matter. I may put some objects together purely because they look prettier to me that way ("ad lib" categorization). That's truly arbitrary. To the extent that taxonomy is constrained by the first kind of uncertainty-reduction, it is empirical and informative. To the extent that it is guided by the latter, it is arbitrary and subjective (or "intersubjective," if most or all people happen to think things look prettier that way). " Obviously, doing the clustering requires deciding which physiological " properties are important, and we can well imagine a different culture " deciding that "having feathers" was a less important property than " "being able to fly" What does "important" mean? Again, if the decision is guided by objective consequences, it is nonarbitrary; if subjective only, it's arbitrary. Social constraints are a special case. Humans are, after all, natural kinds. So the kinds of sanctions they impose on one another are "natural" too. Hence if my speech community tells me that "being able to fly" picks out an important category X, and they test me on it in school, etc., then objective consequences dictate that I better get it right. [Recall that the original issue here was whether or not "classical" features underlie our categorizations, not whether the features (or categories) are chosen for nonsocial or social reasons; it is the objective, external existence of those features that the classicist must be prepared to defend, not the basis for their selection.] " higher-order classifications like "bird" are human creations, not " directly observable distinctions that are mandated by nature. They may or may not be human creations, but they must be based on objectively observable features if they are to be reliably picked out (as they are). " I doubt I could identify, say, a platypus from sight alone. Yet, that " doesn't stop me from knowing things about platypuses... I'm not " restricted to making categorization decisions from sense data alone - I " have the capability to use language, and to know that object X is a " platypus because I was explicitly told that object X is a platypus. I'm nowhere suggesting that all categorization is restricted to "sense data" alone but rather that it is GROUNDED in sensory features. Once grounded, a symbol system is free to rise to ever higher levels of abstraction. I need never have seen a platypus to know and speak about them. But I do need to have grounded categories for "bills," "fur," "egg-laying," and whatever other features pick out the platypus (or grounded categories for whatever features pick out those features, or...etc.). That's exactly the capability that a grounded symbol system for making propositions about category membership (language) gives you. But this capability cannot be taken for granted either, any more than the ability to categorize can; it must be explained (and my symbol grounding theory is one candidate explanation). " One definition of "bird" is all animals that have feathers (another is " all descendants of Archaeopteryx). But the fact that the category is " well-defined does not mean it is not arbitrary. Two different senses of arbitrary seem to be at issue here, but only one is relevant to the problem of the internal representation of categories: The reason we single out a given feature and sort objects in the world according to it may be arbitrary: A dictator may have decreed that we must worship all creatures that exceed his own weight; if he has the power to enforce his decree, then there are dire consequences for us if we fail to detect and act according to this feature. Such a category would be arbitrary in the sense that it did not really pick out a natural kind (since there is nothing special about the dictator's weight or about objects that exceed it), but it would nevertheless be an all-or-none category with perfectly "classical" features (within the limits of our senses and weighing instruments). [The dictator might also have decreed that we must worship creatures that exceed his height OR weight: This too would be a perfectly classical category, with all members sharing the property of exceeding either the dictator's height or his weight.] With nonarbitrary categories, nature is the dictator. Apart from that, there is no difference between categories that are "arbitrary" and "nonarbitrary" in this first sense (at least not for the cognitive theorist concerned with explaining how categorization is accomplished by the head; there may be a difference for the ontologist or the physicist, but their concerns should not be conflated with the epistemic concerns of the cognitive theorist). The second sense of arbitrary would be one in which there really were no objective features subserving an all-or-none distinction -- no objective consequences whatsoever arising from miscategorization: Humpty Dumpty's dictum that words mean what I want them to mean. Or an "X" is whatever I say is an X. It is only arbitrary subjective categories of the latter kind (what I've called "ad lib" categories) that might truly lack classical features. And although it is not their intention, I believe that the incoherent sort of category representation recommended to us by those who think categories are represented nonclassically would be arbitrary in this second sense. -- 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