Q&A: “Rule of thumb” origin

Each week here at the Australian Writers’ Centre, we dissect and discuss, contort and retort, ask and gasp at the English language and all its rules, regulations and ridiculousness. It’s a celebration of language, masquerading as a passive-aggressive whinge about words and weirdness. This week, we're all thumbs…

Q: Hey AWC, we cover a lot of “rules of thumb” about the English language in these chats, right?

A: That’s correct.

Q: So, WHY are they called rules of thumb? 

A: It’s because many of the rules suck, just like a baby does to a thumb.

Q: Really?

A: No, of course not. But it is a good question. The Macquarie Dictionary defines a “rule of thumb” as “a rule based on experience or practice rather than on scientific knowledge.”

Q: That’s it. But where’s it from?

A: One false theory is rather specific, suggesting that the “rule” in question was created by an 18th century lawmaker named Sir Francis Buller.

Q: What was his rule?

A: This is where it gets weird. This lawmaker, dubbed “Judge Thumb” by cartoonists in his day, supposedly ruled that a man was legally permitted to beat his wife, provided he used a stick that was no thicker than his thumb.

Q: Ouch.

A: In actual fact, he never said such a thing and there was never such a law. However, this early example of “fake news” was often cited in legal cases of domestic abuse – even being misquoted right up until the end of the 20th century. It almost forced the phrase to be “cancelled” because people assumed it came from these dodgy beginnings. All rather unfortunate.

Q: So where DID the rule of thumb come from then?

A: It actually goes back to the 16th century; a time when rulers weren’t in ready supply.

Q: What do you mean? King Henry VIII and Queen Elizabeth were rather prominent rulers during this time. Also Mary Queen of Scots, King Charles of Spain and the Emperors of the Ming Dynasty in China.

A: Nice history skills. But ummm, no, we’re talking about the type you might buy from a stationery supply shop. With measurements on it.

Q: Oooooooh. THAT kind of ruler. My bad. Please continue.

A: So it was during this time that the width of a thumb was often used as a measure of one inch – especially in the cloth trade. The phrase “rule of thumb” likely relates to this, although it wouldn’t appear in English until the 1680s.

Q: But why a thumb if it’s just about experience vs science?

A: Well, it’s really about a “rough measure” of something – like measuring something with your thumb and calling it an inch. So an example of a rule of thumb might be “two handfuls of rice for one portion” or “drink eight glasses of water a day”.

Q: Oh, my uncle tried that and nearly died. No one told him not to ingest the glass, you see.

A: Um, right. Anyway, other “rules of thumb” are more figurative, such as “don’t go swimming for half an hour after you eat”, “look both ways before you cross the street” or “don’t start a new project on a Friday” and so on.

Q: Actually, I think he swallowed those glasses ON a Friday! That must have been where he went wrong…

A: Anyway, there are a few other origin stories describing other literal rules of thumb. One asserts that it came from millers, who would test the grind of the flour by rubbing it between their finger and thumb. Another comes from brewers who would dip their thumb into their batch of beer to test its temperature.

Q: Fascinating! Also the makings of a good beer batter…

A: And speaking of battering, the best rule of thumb however is not to believe everything you read on the origin of a phrase – as even to this day, many websites still quote the Judge Thumb wife-beating law as the correct origin.

Q: So in summary, it has nothing to do with sticks but rather a simple metaphor that relates to a “rough measure or rule” for something?

A: That’s right. “Rules to live by” – not backed by science, but likely to stop you from getting hit by a car when crossing the street or avoiding a stomach ache in the pool.

Q: But just don’t eat the glass if you’re doing that “eight glasses of water” one, right?

A: Most people don’t eat glasses, as a rule of thumb.

Q: Well, I give today’s chat a thumbs-up!

A: Actually, did you know that originally the “thumbs-up” sign was associated with death?

Q: B-b-but Gladiator and Russell Crowe?

A: That was actually an oversimplification based on a 1870s painting called Pollice Verso by Jean-Léon Gérôme. The painting depicted a crowd giving the thumbs-down to the victorious gladiator, but in fact historically there was no such gesture. A “thumbs-up” actually meant the gladiator was put to death, while a concealed thumb meant they were saved. 

Q: So when did “thumbs up” become a good thing?

A: It wasn’t even used as a gesture until the end of World War I – was first seen used by American pilots (above the engine noise) to indicate everything was good to go. The phrase “thumbs up” itself was first recorded in the Oxford English Dictionary in 1917 – again meaning “everything is fine with me” – similar to what it means today.

Q: So it’s been popular for only 100 years or so?

A: Well actually, even that’s not entirely true. It apparently faded from popularity during the middle of the 20th century, and its comeback in the 1970s is actually credited to the shark-jumper himself, Fonzie from the TV show Happy Days!

Q: “Ayyyyyyy”. But what about hitchhikers?

A: Thumbing a ride became popular in the 1920s – as the car became a common method of transport. Of course, here the thumb didn’t mean the same thing – it was purely used to point in the direction of where you wanted to go. In 1927, an American newspaper referred to these kinds of travellers as “thumb-pointers”. Another called them “thumb-jerkers”, who would “‘thumb’ their way from coast to coast.”

Q: And I think in some countries, using the “thumbs-up” symbol is considered offensive, right?

A: That’s true, in places like Iran, Iraq and Afghanistan for example. Although in more recent times, social media has helped make thumbs synonymous with “like” and “dislike” – no longer a matter of life or death.

Q: Well, we sure covered thumb ground today. Let’s do it again thumb other time!

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