Date:  Mon, 7 Apr 1997 09:02:01 -0400
From:  Jesse T Sheidlower <jester[AT SYMBOL GOES HERE]PANIX.COM>
Subject: Re: Rule of Thumb

_Rule of thumb_ is a fascinating phrase, because the
ridiculous-sounding folk-etymology (sc. that it's based
on an old English law that a man was allowed to beat
his wife as long as the stick he used was thinner than
his thumb) has some basis in fact.

First, the phrase _rule of thumb_ is not from this alleged law.
However, reference to this practice is found in several
places in English and American court cases from the late
eighteenth century onwards. It does not seem to have been
an actual law, but was seriously belived by some people to
be so.

The folk-etymology based on this practice apparently stems
from a mid-1970s NOW report that mentions the _practice_
and calls it, apparently jocularly, a "rule of thumb." It
did not say that that was the origin of the phrase, but it
seems to have been misinterpreted that way.

There's a short summary of this question at
http://www.randomhouse.com/jesse/961108.html ,
and a long discussion, with citations from the relevant cases,
at
http://www.urbanlegends.com/language/etymology/rule_of_thumb.html

Jesse Sheidlower
<jester[AT SYMBOL GOES HERE]panix.com>