Trying to get a handle on ‘rule of thumb’ origin

Q. When we talk about a standard or principle that’s widely accepted yet has not been proved scientifically nor is strictly accurate, we often call it a “rule of thumb.” For example, the Rule of 72 says you can estimate how many years it will take your money to double by dividing 72 by the interest rate at which it’s invested. It’s a handy rule of thumb. Where did that phrase come from?

A. Wordsmiths have been trying to put their finger on the exact origin of that phrase for decades without success.

The most popular theory seems to be that centuries ago carpenters used either the width or the first joint of their thumbs as a quick way to measure an inch. It wasn’t exact, but it served the purpose pretty well when a ruler wasn’t handy. Hence, a rule of thumb — and there’s a strong basis for this theory in a number of languages. In French, for example, “pouce” can mean both “inch” and “thumb.” In Italian, it’s “pollice,” in Czech it’s “palec” and in Hungarian it’s “huvelyk.” Very similar words also can be found in numerous other tongues from Sanskrit to Thai.

As a result, as early as 1685, James Durham wrote in his “Heaven upon Earth,” “Many professed Christians are like foolish builders, who build by guess and by rule of thumb.” Not surprisingly, the phrase is common in other languages, including Italy (“regola del pollice”) and Germany ( “faustregel,” a variant “rule of fist”).

Others point to farmers as the originators. To germinate properly, seeds should be planted at a certain depth. Farmers, however, are not going to stick a ruler down every hole they dig. Instead, they use their thumb to measure an approximate but reasonably reliable depth gauge.

But like a rule of thumb, these theories are only logical guesses.

“The origin of the phrase remains unknown,” writes Gary Martin on his popular website, The Phrase Finder” (www.phrases.org.uk). “It is likely that it refers to one of the numerous ways thumbs have been used to estimate things — judging the alignment or distance of an object by holding the thumb in one’s eyeline, the temperature of brews of beer, measurement of an inch from the joint to the nail to the tip, or across the thumb, etc.”

An important final note: Since about the 1970s, an urban myth has arisen that “rule of thumb” refers to some old English law that permitted husbands to lash their wives for misbehaving as long as the whip was no thicker than a thumb. This reference apparently stems from a 1782 satirical cartoon (“Judge Thumb”) by James Gilray, in which he criticizes Sir Francis Buller, a harsh and impatient English judge, for allowing such beatings. However, there is some question whether Buller ever made such a ruling.

Besides, the phrase predates Buller by a century and established law long forbade spousal abuse. Even before King Charles II took the English throne in 1660, English law allowed only “moderate correction” (confinement) and specifically outlawed beatings. In 1641, the Massachusetts Body of Liberties stated, “Every married woman shall be free from bodily correction or stripes by her husband, unless it be in his own defense from her assault.” Such standards were reiterated in later court rulings in Mississippi and North Carolina.

For a more detailed explanation, see Cecil Adams’ answer at www.straightdope.com.

Q. What became of Sara Dayley, the morning traffic reporter on KSDK-TV?

A. With 3-year-old Dax and Cade about to turn 1, Mom Sara was no doubt growing weary of her own early evening bedtimes and 1:30 a.m. wake-up alarms. So after five years at KSDK, the daughter of former Cardinal hurler Ken Dayley left the station May 20 to become the community liaison officer with West County EMS & Fire in Manchester, Mo.

Racing fans likely know that Dayley, who grew up in St. Louis and has a degree in mass communications from the University of Tampa, was heavily involved in motorsports at one time. After covering the Super Bowl champ Tampa Bay Bucs and NHL champ Tampa Bay Lightning more than a decade ago, she became a pit reporter for, among others, Monster Jam and Nitro Jam and host of “Lucas Oil on the Edge” and “The ADRL Series,” which were filmed in Chicago.

Today’s trivia

You probably know that on his first voyage Christopher Columbus left Spain with three ships, the Pinta, Nina and Santa Maria. How many ships did he lead on his second trip to the New World?

Answer to Wednesday’s trivia: Many people say politicians often are just bags of wind, so what better city to host a political convention than Chicago, the Windy City? Of the 86 national political conventions since 1832, Chicago has been far and away the favorite locale, hosting 25. However, considering the current political climate, you may be surprised to learn that the Republicans have chosen it more often than the Democrats, 14-11, even though the GOP hasn’t met there since 1960.

Baltimore, a favorite early in the nation’s history, is a distant second with nine, including the very first convention in 1832 by the Democrats (the modern Republican party did not come together until 1856). However, the home of the Orioles hasn’t seen one since Woodrow Wilson was nominated in 1912. Tied with Baltimore is Philadelphia, although the City of Brotherly Love will have the runner-up spot all to itself after the Democrats meet there in July 2016.

Fourth place goes to New York City, which saw the Republicans nominate George W. Bush for a second term in 2004 during the Big Apple’s sixth political convention. And in fifth place? Just look across the river — St. Louis, which hosted Democratic meetings in 1876, 1888, 1904 and 1916 and a Republican confab in 1896.

This story was originally published May 27, 2015 at 2:25 PM with the headline "Trying to get a handle on ‘rule of thumb’ origin."