Rule of Thumb — Where did that come from?

I’ve had this one completely wrong for years.

Last week ’rule of thumb’ was requested. I didn’t want to do it at first. Anyone who has seen Boondock Saints as many times as I have already thinks they know what rule of thumb means, and it’s not good. But then I looked into it and realized that I knew very little.

We use it to mean a general practice or a standard. It’s a tip or a trick of a particular subject, usually obtained by experts of that subject through experience or mentoring.

That’s how we use it, but where did it come from?

A lot of people, myself included, believed ‘rule of thumb’ referenced a law from the 1700s that allowed men to legally beat their wives as long as they used a stick no wider than their thumbs.

My first hint should have been the lack of legends about women cutting off the thumbs of their husbands. Sorry, Jeremiah, but you can’t beat your wife because everything is wider than your thumb nubs.

Fact is, there’s no record of a ‘rule of thumb’ law ever existing. The closest thing to evidence is a satirical cartoon published by James Gillray in 1782. It showed judge Sir Francis Buller holding a bundle of sticks. Allegedly, Buller had ruled it legal for a man to ‘moderate corrections’ with a stick no wider than his thumb. However, there’s no actual record of that ruling. It’s possible Gillray was right but the man created satirical caricatures for a living. That’d be a bit like taking everything Stephen Colbert says as utter truth.

What really destroys this myth for me is a reference to rule of thumb that dates back 100 years before Gillray’s cartoon.

In 1685 an author by the name of J. Durham wrote, “Many profest Christians are like to foolish builders, who build by guess, and by rule of thumb.”

The whole thing came from lazy carpenters!

Why use a measuring tape—or whatever the hell they measured with back then—when your thumb is very roughly an inch? Okay, depending on who you are, maybe not an inch but close enough, right?

You’d better be the only guy on that job, or only hire guys with the same size thumbs. If you send Johnny hammer-thumbs and Stan baby-hands to each rip a 12-inch board, your shit’s going to be crooked.

So if you’ve ever resisted saying ‘rule of thumb’ because of its connection with spousal abuse, resist no longer. Lazy carpenters aren’t a good thing, but at least they don’t deserve to have their thumbs cut off.

If there’s a saying you’d like me to look into, my rule of thumb is to leave it in the comments below.