Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!seismo!rutgers!ucla-cs!zen!ucbvax!OZ.AI.MIT.EDU!MINSKY
From: MINSKY@OZ.AI.MIT.EDU
Newsgroups: comp.ai.digest
Subject: Natural Kinds (Re: AIList Digest   V5 #186)
Message-ID: 
Date: Wed, 22-Jul-87 10:43:00 EDT
Article-I.D.: MIT-OZ.MINSKY.12320404487.BABYL
Posted: Wed Jul 22 10:43:00 1987
Date-Received: Tue, 28-Jul-87 00:48:18 EDT
References: 
Sender: daemon@ucbvax.BERKELEY.EDU
Distribution: world
Organization: The ARPA Internet
Lines: 42
Approved: ailist@stripe.sri.com


About natural kinds.  In "The Society of Mind", pp123-129, I propose a
way to deal with Wittgenstein's problem of defining terms like "game"-
or "chair".  The basic idea was to probe further into what
Wittgenstein was trying to do when he talked about "family
resemblances" and tried to describe a game in terms of properties, the
way one might treat members of a human family: build, features, colour
of eyes, gait, temperament, etc.

In my view, Wittgenstein missed the point because he focussed on
"structure" only.  What we have to do is also take into account the
"function", "goal", or "intended use" of the definition.  My trick is
to catch the idea between two descriptions, structural and functional.
Consider a chair, for example.

  STRUCTURE: A chair usually has a seat, back, and legs - but
     any of them can be changed in so many ways that it is hard
     to make a definition to catch them all.

  FUNCTION: A chair is intended to be used to keep one's bottom
     about 14 inches off the floor, to support one's back
     comfortably, and to provide space to bend the knees.

If you understand BOTH of these, then you can make sense of that list
of structural features - seat, back, and legs - and engage your other
worldly knowledge to decide when a given object might serve well as a
chair.  This also helps us understand how to deal with "toy chair" and
such matters.  Is a toy chair a chair?  The answer depends on what you
want to use it for.  It is a chair, for example, for a suitable toy
person, or for reminding people of "real" chairs, or etc.  

In other words, we should not worship Wittgenstein's final defeat, in
which he speaks about vague resemblances - and, in effect, gives up
hope of dealing with such subjects logically.  I suspect he simply
wasn't ready to deal with intentions - because nothing comparable to
Newell and Simon's GPS theory of goals, or McCarthy's meta-predicate
(Want P) was yet available.

I would appreciate comments, because I think this may be an important
theory, and no one seems to have noticed it.  I just noticed, myself,
that I didn't mention Wittgenstein himself (on page 130) when
discussiong the definition of "game".  Apologies to his ghost.