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Topic: Plausibility Arguments
Replies: 11   Last Post: Mar 14, 1997 10:04 AM

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Steve Cottrell

Posts: 97
Registered: 12/6/04
Re: Plausibility Arguments
Posted: Mar 13, 1997 9:37 AM
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> Date sent: Wed, 12 Mar 97 23:55:28 -0700
> From: Lou Talman <>
> To: alper@Csli.Stanford.EDU,
> Subject: Re: Plausibility Arguments>


> The really interesting, and difficult, question is this: How should
> we deal with students who invent their own "plausible, convincing
> arguments" supporting "outright falsehoods"?
> The question is interesting because students who are capable of
> such things (almost always innocently, of course) are very interesting
> people to teach.
> The question is difficult because it means we must recognize the
> outright falsehood>

> I maintain that the most effective way to deal with the situation is to
> present the "prover" with an example that clearly contradicts what has
> allegedly been proved. And then step aside.
> At least for a while. Noticeably longer than the "prover" likes.
> --Lou Talman

That strategy was used regularly in a graduate topology class I took
years ago. The professor, Lawrence Fearnley, was a master at
creating a diagram or sketch. His usual approach was to listen
carefully to the student present am argument. Then if no one,
including the student presenter, saw the error, he would step to the
board and draw. His comment was usually something to the effect
that "Let me see if I can illustrate." Then he would produce a
sketch, step back himself, and look at your argument and his sketch,
and wait. Very effective. The "step aside" strategy that you
suggest is powerful.

Oh, yes. Sometimes he WAS just illustrating something that had been
done correctly, so we always examined his drawings VERY carfully.

Of course, we were trying to present good mathematical proofs, not
just plausibility arguments, but the counter-example strategy is
effective in both settings. In fact, we often were presenting
plausibility arguments with loopholes where we should have been doing
mathematical proofs.

Steve Cottrell
Mathematics Supervisor K-12
Davis School District
45 East State Street
Farmington, UT 84025

Phone 801-451-1123
Fax 801-451-1333

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