From: bill@warthog.as.utexas.edu (Bill Jefferys)
Subject: Re: Occam's Razor
Date: Wed, 27 Sep 2000 11:24:17 -0500
Newsgroups: sci.math
Summary: [missing]

At 9:50 AM -0500 9/26/00, Axel Harvey wrote:
>On Tue, 26 Sep 2000, David C. Ullrich wrote:

>Yes. Occam's razor has been somewhat over-extended lately to mean a lot
>of things Occam probably didn't intend.
>
>>       What was the original Latin? Something about 
>> "entities shall not be multiplied without reason" or some
>> such, meaning we should not invent new causes if
>> the old ones suffice.
>
>Entia non sunt multiplicanda praeter necessitatem. "Entia" could be
>"concepts" in modern English--or why not simply "things"?
>
>No more concepts should be used than are necessary (understood: for the
>argument being advanced).

Occam (Ockham) did not, in fact, write this. This version of the Razor is
from  the pen of John Ponce of Cork, written in 1639, several centuries
after Ockham.

Ockham did write the following:

  "Pluralitas non est ponenda sine necesitate"--"Pluralities should not be
proposed without necessity."

and

  "Frustra fit per plura quod potest fieri per pauciora"--"It is vain to
do with more what can be done with less."

The basic idea was also stated in various forms by contemporaries of
Ockham. See W.M. Thorburn, "The Myth of Occam's Razor," _Mind_ 27:345-353
(1918).

There is a sense in which Ockham's Razor can be considered a conclusion of
Bayesian reasoning. See [Jefferys, W.H. and Berger, J.O., "Ockham's Razor
and Bayesian Analysis," _American Scientist_ 80, 64-72 (1992)]. A draft
version of this article can be found by following the "selected papers"
link on my website.

Bill

-- 
Bill Jefferys/Department of Astronomy/University of Texas/Austin, TX 78712
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