Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!decvax!tektronix!hplabs!ucbvax!btl.CSNET!ether.allegra
From: ether.allegra@btl.CSNET.UUCP
Newsgroups: mod.ai
Subject: non-monotonic reasoning
Message-ID: <8611080830.AA25848@ucbvax.Berkeley.EDU>
Date: Thu, 6-Nov-86 13:17:14 EST
Article-I.D.: ucbvax.8611080830.AA25848
Posted: Thu Nov  6 13:17:14 1986
Date-Received: Sat, 8-Nov-86 20:24:12 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 30
Approved: ailist@sri-stripe.arpa



John Nagle, in a recent posting, writes:
>         Non-monotonic reasoning is an attempt to make reasoning systems
>  less brittle, by containing the damage that can be caused by
>  contradiction in the axioms.  The rules of inference of non-monotonic
>  reasoning systems are weaker than those of traditional logic.  

Most nonmonotonic reasoning formalisms I know of (default logic,
autoepistemic logic, circumscription, NML I and II, ...) incorporate
a first-order logic as a subset.  Their rules of inference are thus
*stronger* than traditional logics'.  I think Nagle is thinking of
Relevance Logic (see Anderson & Belnap), which does make an effort
to contain the effects of contradiction by weakening the inference
rules (avoiding the paradoxes of implication).

As for truth-maintenance systems, contrary to Nagle and popular
mythology, these systems typically do *not* avoid contradictions
per se.  What they *do* do is prevent one from 'believing' all
of a set of facts explicitly marked as contradictory by the
system using the TMS.  These systems don't usually have any
deductive power at all, they are merely constraint satisfaction
devices.


David W. Etherington
AT&T Bell Laboratories
600 Mountain Avenue 
Murray Hill, NJ 07974-2070
ether%allegra@btl.csnet