Rule of thumb
A rule of thumb is an easily learned and easily applied procedure for approximately calculating or recalling some
value, or for making some determination. Compare this to heuristic, a similar
concept used in mathematical discourse, or in computer science, particularly in algorithm design. See also mnemonic.
The term "rule of thumb" or similar exists in many languages and cultures. Its likely origin is that the thumb is often
used for rough measurement by carpenters, seamstresses, and many others. In fact, the measurement of an inch is believed to have been derived from the distance between the tip of the thumb and the first joint. Rules
of thumb such as the right hand rule in electromagnetics are also used as mnemonic devices. This usage, of course, is of more recent vintage. For most people, the crooked thumb held out at
arm's length subtends an angle to the horizon roughly equal to one hour of time - in other words if the distance of the sun is a
thumb's length (from tip to first joint) above the horizon, it is about one hour until sunset.
Myths about origins of term
It is often claimed that the term originally referred to the maximum size of a stick with which it was permissible for a man
to beat his wife. This claim has been debunked, for instance by Christina Hoff Sommers in her book Who Stole Feminism?
(1994 ISBN 0684801566). In particular Sommers notes that there is no mention of this in the legal commentaries of
William Blackstone.
The popular etymology of the expression or its urban legend may have received a boost in the following quote from Del Martin of the National Organization for Women:
- "In America, early settlers held European attitudes towards women. Our law, based upon the old English common-law doctrines,
explicitly permitted wife-beating for correctional purposes. However, certain restrictions did exist and the general trend in the
young states was toward declaring wife-beating illegal. For instance, the common-law doctrine had been modified to allow the
husband 'the right to whip his wife provided that he used a switch no bigger than his thumb' -- a rule of thumb, so to speak"
-
- —Del Martin, Battered Wives Volcano Press, 1976, page 31.
Regardless of whether Martin's analysis of old English common-law doctrines and possibly even her facts, are accurate, there
is no evidence that she suggested this usage was the origin of the expression under consideration. However the legend persists.
For example:
- "Until the 19th Century, there was a charming little rule of thumb that applied to family life. A man was allowed to beat his
wife as long as the stick he used was no wider than a thumb."
-
- —Ellen Goodman, Washington Post, April 19, 1983.
- "In state courts across the country, wife beating was legal until 1890. There was a rule of thumb, by which courts had
stated a man might beat his wife with a switch no thicker than his thumb."
-
- —Chicago Tribune, March 18, 1990.
See also
External links
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