Many women have been told that the term “rule of thumb” has its origins in ancient English law and that it was a rule limiting the thickness of a stick with which a man could use to legally beat his wife. I was told this by a professor of legal history at Cambridge University in England, so I saw no reason to doubt the tale.
If I’d read more recent research on the subject, I’d know better.
To begin with, the Oxford English Dictionary shows the first use of the phrase “rule of thumb” occurring in 1692. This is far from an ancient legal concept—in fact, for British law, I’d say it’s relatively recent. But in 1692 the phrase was not used with a legal connotation at all. It’s appears in a book about fencing and it refers to a man taking action by rote, without giving it much thought. The phrase was also used in 1721 in a book of Scottish proverbs with a meaning equivalent to practical use.
Where did the phrase originate? Some evidence suggests that the “rule of thumb” refers to a method by which brewers would test the readiness of their beer, by sticking a thumb in it. Others suggest that it refers to a carpenter taking measurement with his thumb. While there’s no definitive answer, there’s also no reason to believe the rule of thumb has evil origins.
However, though the phrase may not have originated with a misogynist concept, that doesn’t mean it was never used that way. A British judge in 1782 supposedly made a remark to the effect that the rule of thumb set the limit on implements for wife beating. He may have been joking. But the joke soon turned on him, as several cartoonists produced vicious caricatures labeling him as “Judge Thumb.” One of these showed a judge handing out sticks as a “cure for a nasty wife” while a wife screams “murder” and her husband retorts “It’s Law you Bitch! It’s not bigger than my Thumb!”
To me, this suggests that the 18th Century cartoonists, at least, thought the idea of an acceptable standard for wife beating was ludicrous. However, others may have disagreed. A 17th Century Irish judge named Marmaduke Coghill once decreed that a man was operating within the bounds of matrimonial privilege when he beat his wife with a particular-sized switch.
And in the 19th Century, American judges cited the “rule of thumb” in three separate cases. In one of these, a North Carolina court declared that a husband had the “right” to beat his wife with a switch so long as it was no larger than his thumb.
So the medieval Brits may get wrongly blamed for creating this “rule,” but it is more “modern” Americans who really put it into practice. Either way, however, it appears that the vast majority of the times that the phrase has been used, it has nothing to do with beating or wives.
Referring to “a rule of thumb” may still offend some women, but I can’t do anything to stop that. I’m just grateful to live in a place and time where it is rare to find an “acceptable” standard for beating anything other than eggs.
Some of the information in this article came from an article by Stephanie Shapiro citing research undertaken by Sharon Fenick as reported in the Baltimore Sun http://articles.baltimoresun.com/1998-04-17/news/1998107056_1_rule-of-thumb-phrase-rule-false-etymology.