Dear Cecil: Recently in a conversation I used the expression "rule of thumb," which I have always understood to mean a technique for arriving at a quick estimate. A woman in our group took me to task, however, informing me that the expression originally referred to an old legal principle that a man was allowed to beat his wife with a stick provided the diameter did not exceed the width of his thumb. When I expressed my disbelief, several others chimed in that they had heard the same story. I'm flabbergasted, Cecil. Is this true? What other seemingly innocent phrases conceal ancient wrongs? It's getting to where I'm afraid to open my mouth. John Santogrossi, Atlanta

Cecil replies:

Ease your mind, bud. “Rule of thumb” doesn’t refer to wife beating. I know it looks like I’m on some sort of rabid antifeminist crusade here. But at least we’ll keep the etymologies straight.

Christina Hoff Sommers explains the whole confused business in her 1994 book Who Stole Feminism? How Women Have Betrayed Women. For more than 300 years “rule of thumb” has meant what most people think it means: any rough-and-ready method of estimating. It’s believed to have originated with woodworkers, who made measurements with their thumbs. For more than 20 years, however, some feminists have maintained that rule of thumb has the darker meaning alluded to above. They say the principle of regulated wife beating was elucidated in the famous legal commentaries of William Blackstone (1723-’80), the basis of much U.S. common law, and that it prevailed in state courts well into the 19th century.

However, in Blackstone, as Sommers notes, there’s no mention of the rule of thumb. We do find the following discussion: “The husband also, by the old law, might give his wife moderate correction … in the same moderation that a man is allowed to correct his apprentices or children … But with us, in the politer reign of Charles the Second [1660-’85], this power of correction began to be doubted; and a wife may now have security of the peace against her husband.” In other words, once upon a time in olde England, a man could beat his wife. But don’t try it now.

Wife beating has never been legal in the U.S. The Massachusetts Bay Colony prohibited it in 1655, religious groups campaigned against it, and vigilantes occasionally horsewhipped men accused of it. Most states had explicitly outlawed it by 1870.

The old permissive approach wasn’t entirely forgotten, however. It was cited in two court rulings, one in Mississippi in 1824, the other in North Carolina in 1874. Both judges referred to an “ancient law” by which a man was allowed to beat his wife with a stick provided it was no wider than his thumb. Where the judges came up with the thumb angle I don’t know; as I say, it’s not found in Blackstone. At any rate, both judges rejected the principle — each found the husband guilty in the wife-beating case he was adjudicating. And neither referred to the old law as the rule of thumb.

The two rulings were mentioned in an article by sociologist Robert Calvert published in the 1974 anthology Violence in the Family (Steinmetz and Straus, editors). In 1976, possibly having seen the article, Del Martin, coordinator of the NOW Task Force on Battered Women, wrote, “Our law, based upon the old English common-law doctrines, explicitly permitted wife-beating for correctional purposes. However … the common-law doctrine had been modified to allow the husband ‘the right to whip his wife, provided that he used a switch no bigger than his thumb’ — a rule of thumb, so to speak.”

“Our law” didn’t permit wife beating, but set that aside. Martin clearly was using “rule of thumb” as a figure of speech — she didn’t claim it actually referred to legalized wife beating. As Sommers shows, however, this detail eluded subsequent retellers of the tale, the most egregious example being the title of a 1982 report on wife abuse by the U.S. Commission on Civil Rights, “Under the Rule of Thumb.” This dark interpretation is now an entrenched popular belief.

So let’s clarify once and for all:

English judges apparently took a more permissive attitude toward wife beating prior to 1660, but this attitude had been rejected by the time of Blackstone’s commentaries, upon which our modern common law relies. Wife beating has never been legal in the U.S. A couple of 19th-century U.S. trial opinions referred to an “ancient law” permitting a husband to beat his wife with a stick not exceeding a thumb’s width but rejected said law. While this alleged rule involved a thumb, it wasn’t the origin of “rule of thumb.”

A complicated story, but one hopes we’ve gotten it straight at last.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.