Where it sits
The phrase has a plain, well-recorded history. The legal story was attached centuries later.
What it doesn't mean
No such law ever existed in England, and the phrase was in print from the 1680s meaning a rough practical method. The Phrase Finder finds no printed link to domestic violence until the 1970s.
It was a rumour. The Victorian legal historian Edward Foss wrote in 1870 that no substantial evidence had been found that Buller ever said it — though the rumour earned him a cruel nickname.
What it really means
Rule of thumb is an everyday phrase for a rough guide: not exact, but good enough from experience. It also carries one of the darkest false etymologies in English.
The myth says that English common law once allowed a man to beat his wife, provided the stick was no thicker than his thumb. That "rule" supposedly gave us the phrase. It's often repeated as a grim fact, and some people avoid the expression because of it.
Why it's wrong. There was no such law. The Phrase Finder notes that English common law once spoke vaguely of a husband "chastising" his wife in moderation, but the rule of thumb was never the law. The phrase itself is much older than the story. It is in print by 1685, in sermons by the Scottish preacher James Durham, who contrasted building "by rule of thumb" with building by square and rule. In 1692, The Compleat Fencing Master describes a man who works "by rule of Thumb, and not by Art". Neither passage has anything to do with violence. The Phrase Finder finds no printed link between the phrase and domestic violence until the 1970s.
Where the myth came from. In the 1780s, a rumour spread that Judge Sir Francis Buller had ruled that thumb-thick sticks were lawful. The cartoonist James Gillray mocked him as "Judge Thumb". No record shows Buller ever said it; the legal historian Edward Foss wrote in 1870 that no substantial evidence had been found. Two centuries later, the rumour and the old phrase were joined together.
What's actually known. People have long used the thumb as a rough measure; Etymonline dates the thumb-as-an-inch idea to around 1500. A rule of thumb is a measurement by hand, not by instrument. The exact origin is uncertain, but nothing in the record supports the legal story.
Where it comes from
- c. 1500
Using the thumb as a rough measure of an inch is attested (Etymonline).
- 1685
The earliest known printed use, in sermons by the Scottish preacher James Durham: building 'by guess, and by rule of thumb … and not by Square and Rule' (Wikipedia, which gives 1685 for this posthumous collection; The Phrase Finder dates the same book to 1658).
- 1692
Sir William Hope's The Compleat Fencing Master: a man who works 'by rule of Thumb, and not by Art'.
- 1782–83
A rumour says Judge Sir Francis Buller ruled a man may beat his wife with a stick no thicker than his thumb; James Gillray caricatures him as 'Judge Thumb'. No record shows he said it.
- 1970s
The phrase is first linked in print to domestic violence, according to The Phrase Finder.
In real life
- As a rule of thumb, she leaves twenty minutes early for anything on the M25.
- The old carpenter's rule of thumb: measure twice, cut once.
- A good rule of thumb for houseplants is to water when the top inch of soil feels dry.
Questions
Q01Does 'rule of thumb' come from a law about wife-beating?
No. There was never such a law in England. The phrase was in print by 1685 meaning a rough, practical method, and The Phrase Finder finds no printed link to domestic violence until the 1970s. The story grew from an 18th-century rumour about a judge.
Q02Where does 'rule of thumb' actually come from?
Probably from using the thumb as a rough measuring tool — Etymonline dates thumb-as-an-inch to around 1500. A rule here means a measuring rule, so 'by rule of thumb' means measured roughly by hand rather than with an instrument. The exact origin is uncertain.
Q03Who was 'Judge Thumb'?
Sir Francis Buller, an 18th-century English judge, rumoured to have said a man could beat his wife with a stick no thicker than his thumb. James Gillray mocked him in a cartoon. There's no record that Buller ever said it.
Q04Is it offensive to say 'rule of thumb'?
The phrase itself has no violent origin. Some people avoid it because the myth is so widely believed — Wikipedia notes efforts were made to discourage it after the 1970s. That's a choice about audience, not about history.
Sources
- What's the origin of the phrase 'Rule of thumb'? — The Phrase Finder.
- thumb (rule of thumb) — Online Etymology Dictionary.
- Rule of thumb — Wikipedia.