Rule of thumb

The error appeared in a number of law journals, and the United States Commission on Civil Rights published a report on domestic abuse titled "Under the Rule of Thumb" in 1982.

During the 1990s, several authors correctly identified the spurious folk etymology; however, the connection to domestic violence was still being cited in some legal sources into the early 2000s.

This belief may have originated in a rumored statement by 18th-century judge Sir Francis Buller that a man may beat his wife with a stick no wider than his thumb.

Wife-beating has been officially outlawed for centuries in England and the United States, but continued in practice; several 19th-century American court rulings referred to an "ancient doctrine" that the judges believed had allowed husbands to physically punish their wives using implements no thicker than their thumbs.

[11][12][13] A modern folk etymology[14] relates the phrase to domestic violence via an alleged rule under English common law which permitted wife-beating provided that the implement used was a rod or stick no thicker than a man's thumb.

[7][a] Twentieth-century legal scholar William L. Prosser wrote that there was "probably no truth to the legend" that a husband was allowed to beat his wife "with a stick no thicker than his thumb".

[3][7][16] In the following century, several court rulings in the United States referred to a supposed common-law doctrine which the judges believed had once allowed wife-beating with an implement smaller than a thumb.

[3] An 1824 court ruling in Mississippi stated that a man was entitled to enforce "domestic discipline" by striking his wife with a whip or stick no wider than the judge's thumb.

[5] While Martin appears to have meant the phrase rule of thumb only as a figure of speech, some feminist writers treated it as a literal reference to an earlier law.

[5][10]: 43  The following year, a book on battered women stated: One of the reasons nineteenth century British wives were dealt with so harshly by their husbands and by their legal system was the 'rule of thumb'.

[5] During the 1990s, several authors wrote about the false etymology of rule of thumb, including English professor Henry Ansgar Kelly and conservative social critic Christina Hoff Sommers,[3] who described its origin in a misunderstanding of Blackstone's commentary.

Man's thumb on a wooden ruler that is marked in inches
An adult's thumb is about one inch wide, so it can be used to estimate the size of an object.
Cartoon of Sir Francis Buller in judges' robes and powdered wig, carrying bundles of rods whose ends resemble thumbs; in the background, a man with a rod raised over his head is about to strike a woman who is running away from him
Cartoon by James Gillray satirizing Sir Francis Buller , 1782: "Judge Thumb; or, Patent Sticks for Family Correction: Warranted Lawful!"