"Rule of Thumb" Origin

What I love most about American idiomatic phrases – other than repeating them, of course – is to learn their respective origins. We all use idiomatic phrases, or metaphors, to explain this reality by relating it to an alternate one. Even if we say them, however, and understand their correct usage, it still surprising to learn where those phrases originated from and what they originally meant.

I have been using "rule of thumb" to apply a commonly used rule or practice to a specific incident, using this approximate knowledge to make a decision.

(Bad) Example: I am not hungry as of yet, but according to rule of thumb I will be requiring three meals and a bottle or two of wine by the end of today.

Awhile back, someone (somewhere) quickly explained to me the phrase's origin. The "rule of thumb" referred to an old British law which gave husbands the permission to beat his wife with a stick no longer than the width of a thumb.

Could this be true? Could my innocent little idiomatic phrase be offending feminists? I did some digging.

Apparently, "rule of thumb" was uttered in public by English judge Francis Buller in 1782, and this was long-believed to be the first utterance of the phrase. Following the comment, Buller was incessantly mocked by political pundits of his time, including the first great political caricaturist James Gillray—who I suppose was his generation's Jon Stewart. Buller even gained the nickname of "Judge Thumb."

If this was the first utterance of "rule of thumb," it would be amazing that it even caught on. Academics and fact-checkers, however, have determined this was not the case.

In 1994, UCLA professor Henry Kelly discovered the phrase at been used nearly a century earlier, debunking any claims that the phrase had originated from law, court, or any court-appointed person.

The New York Times explains:

That's because its first appearance in print is cited in the o.e.d. as 1692, nearly a century before Gillray's ''Judge Thumb.'' Sir William Hope, in ''The Compleat Fencing Master,'' wrote, ''What he doth, he doth by rule of Thumb, and not by Art.'' It was reported in 1721 in Kelly's Scottish Proverbs: ''No Rule so good as Rule of Thumb.'' The meaning is ''a roughly practical method, or an assertion based on experience.''

Origin? Could be that carpenters used the width of their thumbs to approximate an inch, or that artists held up their thumbs to gain perspective on a distant object, or that gardeners used their green thumbs as guides to depth of seeding. The idea that rule of thumb is derived from an early form of spousal abuse is in error. It's ''folk etymology,'' amusing, even plausible with its first citation two centuries old, but inaccurate.

For those of you who, for whatever reason, are attracted to rules of thumb, there is a Web site dedicated solely to providing hundreds of trivial rules, facts, and measurements that were used as rules of thumb.

As for the phrase itself, this should hopefully mean feminists have one less thing to worry about in the world. Heck, I can keep using the phrase without feeling liberal guilt!