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From: mclean@NRL-CSS.ARPA (John McLean)
Newsgroups: comp.ai.digest
Subject: Natural Kinds
Message-ID: <8707161942.AA13065@nrl-css.ARPA>
Date: Thu, 16-Jul-87 15:42:11 EDT
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Posted: Thu Jul 16 15:42:11 1987
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Even "recent" philosophical discussions of natural kinds go back 20 years
and much further if you count Nelson Goodman's stuff on projectibility of
predicates (why do we assume emeralds are green and not grue, i. e.,
green until the year 2000 and then blue?) or much of the stuff written
in response to Hempel's problem whether a nonblack nonraven could could
count as a confirming instance of the claim that all ravens are black (since
the claim that all P's are Q's is logically equivalent to the claim that
all nonQ's are nonP's).  But I think you can also view much of what Plato
had to say about forms and what Aristotle had to say about substance as
being concerned with the problem of natural kinds as well.

However, I think the issue being raised about recognizing penguins,
chairs, etc. goes back to Wittgenstein's _Philosophical_Investigations_:

   For if you look at them you will not see something that is common to
   all, but similarities, relationships, and whole series of them at
   that...I can think of no better expression to characterize these
   similarities than "family resemblance"...

John McLean