Newsgroups: sci.logic,comp.ai.philosophy
Path: cantaloupe.srv.cs.cmu.edu!das-news2.harvard.edu!news2.near.net!cat.cis.Brown.EDU!brunix!cs!rv
From: rv@tahoe.cs.brown.edu (rodrigo vanegas)
Subject: Re: Expressibility (was "Penrose's new book)
In-Reply-To: minsky@media.mit.edu's message of Thu, 27 Oct 1994 02:06:38 GMT
Message-ID: <RV.94Oct26231109@tahoe.cs.brown.edu>
Sender: news@cs.brown.edu
Organization: Brown University Department of Computer Science
References: <1994Oct26.172830.3987@oracorp.com> <1994Oct27.020638.28742@news.media.mit.edu>
Date: Thu, 27 Oct 1994 03:11:08 GMT
Lines: 27
Xref: glinda.oz.cs.cmu.edu sci.logic:8727 comp.ai.philosophy:21414

In article <1994Oct27.020638.28742@news.media.mit.edu> minsky@media.mit.edu (Marvin Minsky) writes:

   Yes, and so far as I can see, all this adds up to: 

	   You can gain consistency only by giving up expressibilty. 

   (See also Daryl's next message.)  In particular, when you try to
   express commonsense ideas that happen to be self-referent you expose
   yourself to diagnalization.  If it were more often understood how
   pervasive this is, then computer science students would be more
   suspicious of first order logic.  When do you need self-reference?
   Certainly when you make up things like

   (1)   the liar's paradox.

   Of course everyone know that this leads to trouble.  But you also need
   it in order to emply advice like

   (2)	"To solve a problem, use heuristics appropriate to that kind
   of problem -- but don't use ones that have led in the past to poor
   results."

I don't understand.  How does (2) make use of self-reference?  

-- 
rodrigo vanegas
rv@cs.brown.edu
