Ever use the expression “rule of thumb”? If you have, I discovered this morning, you’re sending a subliminal message that you support wife-beating. I kid you not.

This amazing piece of linguistic nonsense came to me by way of Georgetown professor Katherine Marshall, who had the misfortune of using the phrase in the hearing of two misinformed female pastors, according to her column at “On Faith” in the Washington Post:

I had blundered, bigtime.

Speaking at an interfaith assembly, I had made the case that women’s welfare would improve much faster if more women were in decision-making positions. A “rule of thumb,” I said, should be 30 percent women among leaders of any institution. With less than that, women are too often fighting tokenism. When the numbers of men and women are balanced, agendas and tone change.

Two women pastors, quite independently, drew me aside right afterwards. The term “rule of thumb”, they told me, came from an ancient common law that limited the size of the switch a man could use to beat his wife: no larger than the diameter of his thumb. Since I was arguing for religious leaders to take action against domestic violence, my use of the phrase was particularly jarring.

The unfortunate professor was unaware of the urban legend status of this, and so simply took the pastors at their word. Turns out that this is one of those “fake but true” stories so beloved of those who like playing “gotcha”:

This has been said to derive from the belief that English law allowed a man to beat his wife with a stick so long as it is was no thicker than his thumb. In 1782 Judge Sir Francis Buller is reported as having made this legal ruling. The following year James Gillray published a satirical cartoon attacking Buller and caricaturing him as ‘Judge Thumb’. The cartoon shows a man beating a fleeing woman and Buller carrying two bundles of sticks. The caption reads “thumbsticks – for family correction: warranted lawful!

It seems that Buller was hard done by. He was notoriously harsh in his punishments, but there’s no evidence that he ever made the ruling that he is infamous for. Edward Foss, in his authoritative work The The Judges of England, 1870, wrote that, despite a searching investigation, “no substantial evidence has been found that he ever expressed so ungallant an opinion”.

So the connection that exists in some people’s mind between the expression and domestic violence is no more valid than the belief of some people that the moon is made of green cheese. But Professor Marshall has been duly chastised:

Embarrassed about my blunder, I consulted Google about the rule of thumb. I learned that I was in plenty of company, much of it good – for example the columnist Nicholas Kristof, who has written powerfully against gender violence, has used it too. And scholars think the phrase probably did not originate with wife beating at all, but with an ancient carpenter’s measure. But I, for one, will not use it again.

Why not? Because some silly people believe something that is patently false? Are we to now have our linguistic freedom curtailed because the purveyors of urban legend will take umbrage? This is not, as one article I saw on this subject this morning said, a “matter of etiquette.” This is a matter of allowing the ignorant to scold people for the exercise of their free speech, claiming that they are being victimized by people with no intention of offending, and who are not in fact doing so except in the minds of the misinformed. I’m all for not offending people, but it degrades discourse when ignorant political correctness is allowed to trump freedom of speech, not to mention reality.