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From: cpshelley@violet.waterloo.edu (cameron shelley)
Newsgroups: comp.ai.philosophy
Subject: Re: LOGIC AND RELATED STUFF
Message-ID: <1991Jun26.173142.3060@watdragon.waterloo.edu>
Date: 26 Jun 91 17:31:42 GMT
Article-I.D.: watdrago.1991Jun26.173142.3060
References: <9106190527.AA17403@lilac.berkeley.edu> <1991Jun26.152830.12273@cis.ohio-state.edu>
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In article <1991Jun26.152830.12273@cis.ohio-state.edu> byland@iris.cis.ohio-state.edu (Tom Bylander) writes:
[...]
>I should mention that I do not believe that logic is going to solve
>all the world's problems.  As many articles have noted, there are lots
>of problems with logic.  However, just because logic has some problems
>doesn't mean that logic is dispensable.  Whether we like it or not,
>modus ponens is still something we will have to take into account.

Curious you should metion modus ponens.  At the CUNY Cog. Sci. conference
this year, there was a session given by a panel of philosophers on the
subject of the psychological reality of some classical rules of logic.
They gave some interesting statistics on when a group of university
students actually performed inference in problems where it was possible.
Modus ponens was more readily used than modus tollens, among other
things.  However, they also gave some counter-examples to the use of
modus ponens, which I don't presently have at hand.  Perhaps some interested
reader can fill me in again.

If correct (and apparently the 'validity' of classical inference is currently
a hot debating point among philosophers concerned with such things) then
the account of modus ponens you're looking for may not be as simple as
	A -> B
	A
	------
	B
in all situations.  Whatever logic does do (or model) in producing interesting
behaviour, it doesn't appear to be enough.

				Cam