Modul 5: Idiom 36: Rule of Thumb

Rule of Thumb

Hi. Let’s take a look at the Idiom, ‘Rule of Thumb.’ What is a Rule of Thumb? Well, it’s an unwritten rule that you have about something. A rule tells you what you must or mustn’t do, or may or may not do in certain situations. For example, this sign represents “No smoking”, so you can not smoke

So what is the origin of this idiom?

Well, the top joint of your thumb is on average equivalent to one inch roughly- which is 2 and a half centimetres. So for this reason it’s been used as a rough form of measurement. Because it is not exactly one inch, it can only be used as a rough estimate or a rough guess…

Take a look at our illustration.

First, look at the thumb. Here we have the rough measurement of an inch-just like in the origin of the idiom. But, why would the hand be pointing? What does pointing suggest? Pointing can be used as a gesture or movement to command someone to do something. The person whose hand it is is setting down a rule. See the exclamation mark too? The rule is not written but it still very strong. And that is a rule of thumb.

Here are some examples before we go to the concept questions…

“By rule of thumb, I don’t work past five o’clock.”

“Julie drinks 4 pints of water every day, but this is just a rule of thumb.” It’s her own ‘unwritten’ rule.

“Jack, can you add two cups of pasta into the boiling water? Don’t worry if it isn’t exact, it’s just a rule of thumb.”

“By rule of thumb my sister won’t spend more than £10 on a bottle of wine but sometimes she’ll treat herself.”

“Violet, you can’t say it’s a rule of thumb if you never actually do it!”

Great.

Let’s look at some situations and check your understanding:

1. It’s Thursday evening and you’re in the supermarket. You don’t usually drink during the week, but you’ve had a really tough day so you buy a beer to enjoy with a film later on. Have you kept to your rule of thumb? No, you haven’t. It’s a Thursday and you’ve bought a beer instead of waiting until the weekend you’re drinking in the week.
2. Derek doesn’t enjoy driving the same way to work every day. He makes a point of finding new routes to keep it interesting. One day, Derek was late for work so he took the quickest, most familiar route to the office. Did Derek stick to his rule of thumb? No, he didn’t, as he drove a route that wasn’t new to him and a route that he’d driven many times before.
3. You’re babysitting your nephew. His parents only let him have one scoop of ice cream after dinner but you have given him two. Did you stick to his parent’s rule of thumb? No, because you gave him more than he’s allowed.
4. Ellis is doing her weekly food shop – she tries to keep her spending below £100. At the checkout, the total comes to £87.14. Did Ellis keep to her rule of thumb for her weekly groceries? Yes, she did as her food bill didn’t exceed – it didn’t go over – £100.
5. “Please can we get a takeaway again? I’m too tired to cook!”, your husband asks. “No,” you say, “you know that we don’t get takeaway more than once a week!”. Half an hour later, you place a bowl of food next to him and it’s homemade spaghetti. Did you keep to your rule of thumb? Yes you did, as you cooked a meal instead of getting a  takeaway.

Great. Now go and practise. See you soon.