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Article 5114 of comp.ai.philosophy:
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>From: markrose@spss.com (Mark Rosenfelder)
Newsgroups: comp.ai.philosophy
Subject: Re: Categories: bounded or graded?
Message-ID: <1992Apr15.172904.3372@spss.com>
Date: 15 Apr 92 17:29:04 GMT
References: <1992Apr14.143822.10246@psych.toronto.edu> <1992Apr15.010721.17700@organpipe.uug.arizona.edu>
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In article <1992Apr15.010721.17700@organpipe.uug.arizona.edu> bill@NSMA.AriZonA.EdU 
(Bill Skaggs) writes:
>  With Wittgenstein in mind, I ask:  what are the invariant features
>that characterize a "game"?
>
>  Wittgenstein, of course, argued that there are none.  His view,
>and an increasing popular view among linguists (see, for example,
>Lakoff's "Women, Fire, and Dangerous Things") is that natural
>categories are not defined by invariant features, but rather
>by radiation from prototypes.  (Thus a bird is anything that is
>sufficiently similar to the prototypical bird, which is something
>like a sparrow.)  I don't want to sound like Mikhail Zeleny, but
>I will go so far as to say that the idea that categories are
>defined by invariant features is no longer really defensible.
>
>  In my opinion the belief that natural categories are defined
>by invariant features leads to all kinds of nasty problems.  

I have a lot of sympathy with the idea of prototypes, but I think they
lead to nasty problems too.  

The basic problem is, there needs to be something besides the prototype
standing behind a word.  At the very least you need a radius: how far
from the prototype can an object be and still be an instance of the
category?  The radius must be different for (say) "terrier",
"dog", and "animal."

If you picture the possible referents of a word as a fuzzy cloud surrounding
the prototype, it seems clear (to me, at least) that the cloud is not always
spherical-- it can be quite convoluted.  For instance, a stool looks more
like the prototypical "chair" than many real chairs.  The problem of
defining the boundary of the cloud begins to resemble the traditional one
of defining features.

Purpose is relevant to the meaning of many words.  A "chair" is above all 
something you can sit on, and that's not a direct physical feature of the 
prototypical referent(s).  

Ostensive definitions are useful for some words (e.g. "dog"), but for others
they are simply annoying.  If you ask someone what "opaque" means, and they
point to their shoes and say "This is," that's not very helpful.  If providing
a prototype is not enough, however, then meaning involves more than prototypes.

I do see prototypes as part of cognition; I think they explain some of the
flexibility of language, and also some of the sense of depth there is to
human knowledge-- the sheer mass of information we have about the words
we know.


