Rule of Thumb (Origin)

What Is the Origin of the Saying "Rule of Thumb"?

The term "rule of thumb" means roughly or approximately.

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Rule of Thumb (Origin)

Examples of Use:

  • As a general rule of thumb, I do not drink coffee after 5pm.
  • A good rule of thumb is that you need a 10% deposit to buy property.
The idiom "rule of thumb" originated in the 17th century. It derives from the practice of making rough measurements with the thumb. The earliest known use of this practice in print appears in "Heaven Upon Earth" in a 1658 sermon by the English puritan James Durham:
  • "Many profest Christians are like to foolish builders, who build by guess, and by rule of thumb and not by Square and Rule."
Of interest, the word for "inch" is the same or similar as the word for "thumb" in many languages. Also, an inch can be measured roughly using the thumb (from the first knuckle to the end of the finger nail).

Competing Theory

In England in the 17th century, a man was allowed to beat his wife with a stick as long as the stick was not thicker than his thumb. This was known as "the rule of thumb."

This theory is strongly refuted by etymologists, who highlight that, even though it was legal for a man to chastise his wife in moderation [sic], the "rule of thumb" has never been the law. However, supporters of this theory claim that, in 1782, Judge Sir Francis Buller made a legal ruling about the "rule of thumb" for beating sticks, which was captured in a satirical cartoon by the English artist James Gillray.
rule of thumb law ruling
Gillray's cartoon shows a man beating his fleeing wife, while Judge Buller (called "Judge Thumb"), carrying two bundles of sticks, watches the pair. The cartoon's caption reads "thumbsticks - for family correction: warranted lawful!"

Detractors of this theory claim the cartoon was designed only to portray Buller's reputation for harsh punishments and not to cite a genuine legal ruling. The detractors also highlight that there are no examples anywhere in print of "rule of thumb" being used in the context of domestic violence, other than as a fanciful explanation for the saying's origin.

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This page was written by Craig Shrives.