English is full of idioms.  The meaning of some of these phrases is self-explanatory.  Others seem completely unconnected from their meaning.  Their origins have been lost or muddled.  One idiom with a controversial past and unclear origin is “rule of thumb.”  The rule of thumb is generally understood to mean a basic guideline to follow rather than a hard-and-fast rule.  It is a phrase used in many contexts, such as cooking, gardening, writing, and parenting.  Pretty much every area of our lives has things that we follow as a general “rule of thumb.”

The phrase became controversial when it was used in descriptions of domestic violence.  It was believed that a judge in England, Sir Francis Buller, once stated that it was legal for a man to beat his wife so long as the stick was smaller than the width of his thumb.  There is no evidence that he ever said this, and this was never the law in England.  The origin of this belief most likely came from a political cartoon published in 1782.  In the 1970’s, feminists writing on domestic abuse began referring to Buller’s supposed statements as the “rule of thumb.”  For this reason, some people believe the idiom’s origin is rooted in violence, and they find the phrase offensive.

The “rule of thumb,” however, dates back much further than the 1970’s.  The first known use in print is from a sermon by James Durham in the 1600’s where he said, “Many profest Christians are like to foolish builders, who build by guess, and by rule of thumb (as we use to speak), and not by Square and Rule.”  The usage here implies the phrase was much older than the sermon.

While the original origin and meaning of “rule of thumb” has been lost, it is most likely that it began as a very literal phrase.  It was once common practice to use specific body parts, such as thumbs, for measurement.  The width of a thumb is about one inch.  The thumb was used as a ruler in textiles, brewing, cooking, and other areas for making quick, imprecise measurements.

Even though the phrase is rooted in measurements, some still believe “rule of thumb” is a violent phrase. The persistence of this myth is evidence that it is a good rule of thumb not to believe everything you hear.

What are some other idioms that seem odd when you think about them?`

Crystal Kelly is a feature writer for Bizarre Bytes with those unusual facts that you only need to know for Trivial Pursuit, Jeopardy, or to stump your in-laws.

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