This is what my English book[1] says (I've condensed the paragraphs so they're a bit shorter and straight to the point.):

Fixed expressions, also known as idioms, are often rather informal. Never use them just to sound fluent or good at English. In a formal situation with a person you do not know, don't say:

'How do you do, Mrs Watson? Do take the weight off your feet.' [sit down]

Instead say: 'Do sit down' or 'Have a seat.'

If I understood the paragraph above correctly, does it mean we are not recommended using idioms in a formal situation? That means, we can only use idioms with friends, family or other people you have known?

[1] Vocabulary In use Upper Intermediate by McCarthy and Felicity O'Dell. Please note the authors are both born in 1947, so I don't know how recent is the book.

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    @gotube Vocabulary In use Upper Intermediate by McCarthy and Felicity O'Dell.
    – user516076
    Oct 14, 2021 at 1:29
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    When you condensed the paragraphs, is there any chance you introduced wording that made it more restrictive than what McCarthy and O'Dell wrote? I'm quite surprised that those writers that that publisher would state something so obviously incorrect. Your average person on the street wouldn't even agree that you should generally avoid idioms in formal settings. The part they got right is, "Never use idioms to sound fluent."
    – gotube
    Oct 14, 2021 at 1:33
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    Ah, sorry, missed the word "often". In that case, I think "sometimes" would have been sufficient. I certainly don't think idioms are informal on average.
    – gotube
    Oct 14, 2021 at 2:36
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    If I hear anyone ever saying "Do take the weight off your feet", I would assume or suspect they're not a native speaker. This is not because it's an idiom, but because it's not a commonly-used variant of the saying and it's needlessly verbose (compare it to how short the given alternatives are). Although these things do tend to vary based on region. Also note that "formal situation with a person you do not know" is saying 2 things: (a) it's a formal situation and (b) it's a situation with a stranger. It doesn't say anything about using idioms in informal situations with strangers
    – NotThatGuy
    Oct 14, 2021 at 10:00
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    Yes, it's definitely an oversimplification to say that English idioms are always informal, as it depends on the idiom. Oct 14, 2021 at 20:59

4 Answers 4


The guidance in the text is, in my view, oversimplified to the point of being incorrect.

Many idioms and fixed phrases are typically used in informal situations. For example "take a load off your feet" (or often just "take a load off") is quite informal. It should not be used in formal situations.

But idioms such as "Good things come to those who wait", "We are going to break new ground", or "They are up in arms", are neither particularly formal nor informal, and may be used on occasions all across the range from very casual to quite formal.

Some idioms and fixed phrases such as: "I am going to play devil’s advocate", "May I have the pleasure of this dance?", or "I am so pleased to meet you" are used mostly in formal writing or on formal occasions. And some fixed phrases are used only on particular formal and ceremonial occasions.

For example:

I have the high honor, and distinct privilege, of presenting the President of the United States.

This is said by the Speaker of the US House of Representatives when the US President is about to address a joint session of Congress (a very formal occasion indeed) and at no other time.

Many ceremonies contain lots of fixed phrases. For example:

Do you, John, take Jessica, to be your lawfully wedded wife, to have and to hold, to love, honor, and cherish, as long as you both shall live?

I would also disagree with the text in saying that an idiom and a fixed phrase are the same thing. I would say that they are not.

The Wikipedia article "Set phrase" begins:

A set phrase (also known as a phraseme or fixed phrase) is a phrase whose parts are fixed in a certain order, even if the phrase could be changed without harming the literal meaning. This is because a set phrase is a culturally accepted phrase. A set phrase does not necessarily have any literal meaning in and of itself. Set phrases may function as idioms (e.g. red herring) or as words with a unique referent (e.g. Red Sea). There is no clear dividing line between a commonly used phrase and a set phrase. It is also not easy to draw a clear distinction between set phrases and compound words.

while the article on "Idiom" begins:

An idiom is a phrase or expression that typically presents a figurative, non-literal meaning attached to the phrase; but some phrases become figurative idioms while retaining the literal meaning of the phrase. Categorized as formulaic language, an idiom's figurative meaning is different from the literal meaning.

An article from study.com reads:

Fixed phrases are phrases in which the wording cannot be changed without sounding odd to native speakers, even if the literal meaning is the same.

Fixed phrases, as a category, also includes idioms, which are fixed phrases that mean something different from their literal definition. Just as with other fixed phrases, you cannot change the wording of idioms, even if the literal meaning would stay the same. Both idioms and other fixed phrases may be tested on standardized tests.


Not all fixed phrases take the form of idioms. Non-idiom fixed phrases tend to be more closely linked to their literal definitions than idioms. One English fixed phrase is 'of its own accord,' meaning 'on its own' or 'automatically.' As you can see, the meaning is closely matched to the literal definition. However, you still cannot substitute words. In the sentence 'The wagon moved of its own accord,' for example, you cannot say 'The wagon moved of its own ability.' This has the same literal meaning, but the phrasing is awkward.

Thus an idiom is a fixed metaphor or allusion, the meaning of which cannot be reliably determined from the meanings of the individual words. But a fixed phrase is a standardized expression with a fixed meaning, but that meaning can often be determined from the words of the phrase.

Idioms are a subset of fixed phrases. That is, all idioms are fixed phrases, but not all fixed phrases are idioms. But often "fixed phrase", is used to mean "a fixed phrase that is not an idiom".

I would agree that using idioms one does not well understand just to appear more fluent is often a mistake.

Therefore, when one learns an idiom, it is a good idea to learn in what situations and circumstances it is appropriate to use. This may include its level of formality, and will include its connotation as well as its denotation. It is often interesting to learn the origin or history of an idiom, but rarely is that essential to using it correctly.

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    I agree with everything in this answer but to me it seems to be lacking a summary/conclusion/something to tie it all together. Something along the lines of "the best advice is that each time you learn an idiom, you should also try to learn if the idiom is specifically informal or specifically formal"
    – Muzer
    Oct 14, 2021 at 9:53
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    I would go so far as to say the quoted text from the OP was written by someone who does not actually understand what an idiom is. It seems to be a common misconception among people without background in linguistics that ‘idiom’ refers to something that is inherently informal. Oct 14, 2021 at 12:36
  • @Muzer conclusion aded. Oct 14, 2021 at 13:30
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    I personally view "Have a seat" as a formal set phrase and idiomatic. It is definitely figurative.
    – Yorik
    Oct 14, 2021 at 21:20
  • It may be worth adding the classic every square (idiom) is a rectangle (fixed phrase) but not every rectangle (fixed phrase) is a square (idiom) analogy
    – TCooper
    Oct 14, 2021 at 22:33

Your book is giving a completely incorrect explanation. It equates "fixed expression" to "idiom," and then suggests that idioms are "often" informal. This is all wrong.

A fixed expression doesn't have to be an idiom. For example, "due diligence" is a fixed expression in English that recently has seen a lot of over-use. If you were buying a car, you would do your due diligence by looking up information about whether that type of car was a good one. This isn't an idiom, but it is a fixed phrase because these two words get used together enough to become locked together in people's minds.

An idiom is a way of saying something in a certain language that isn't logically predictable, and that you wouldn't be able to guess based on looking up the individual words in a dictionary. For example, if you say "I cut my meat," it suggests that you cut off one piece, while "I cut up my meat" means that you cut it into lots of little pieces on your plate, as if you were going to feed it to a baby. The use of "up" in this phrase isn't logical, it couldn't be guessed by looking up "cut" and "up" in a dictionary, and someone who grew up speaking French would never guess that English speakers would say it this way. Computer languages have idioms. For example, in C I can say "x+=1," which means to increase x's value by 1, but that's a C idiom that wouldn't work in a language such as BASIC. An English idiom doesn't have to be a multi-word phrase. It can be a single word. For example, I can say, "That's a sorry looking tree," where "sorry" is an idiom meaning that the tree looks damaged, sick, or old.

Idioms and fixed phrases are not always informal. "Cut up" is an idiom, but it's not informal. "Due diligence" is a fixed phrase, but it's not informal.

What your book is trying to advise you not to do is to memorize idioms in English without understanding all the nuances of how they're used. This is actually good advice for native speakers as well: say things in the simplest possible way.


As a non-native speaker of English, I avoid using idioms in anything close to "formal" and do not like to be on the receiving side either.

Simple sentences where "meaning of the sentence = sum of meaning of the words" are sometimes already difficult to understand. If you sprinkle this with idioms that the other party is expected to know, you may end up conveying a message radically different from the intended one.

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    Yes, if you are having trouble understanding someone, do not say I Can Has Cheezburger? Oct 14, 2021 at 17:48
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    Idioms can indeed confuse those who do not know them, and when used incorrectly can produce confusion or miscommunication. But to fail to use appropriate idioms may sound stilted or odd. One must learn many idioms to use the language well. This is just as true in informal as in formal situations. Oct 15, 2021 at 18:07

Specifically, yes but generally, no.

In the specific situation of greeting anyone with whom you aren't familiar, do say 'Do sit down' or 'Have a seat' and don't say "… take the weight off your feet.'

Because the difference between 'Do sit down' or 'Have a seat' and "… take the weight off your feet…' can't be measured, it also can't be transferred to any other idiom, much less to idioms in general.

The point of idioms is broadly that they are specific phrases that for whatever reason, break normal rules. In this case, the broken rule isn't one of grammar, nor even semantics, but solely of manners or social politics.

For that reason, the Question might better be Asked in English Language Usage than here in ELL

Quite separately, please note the (huge) difference between "how recent…" *

  • is and anything useful.

We all clearly know "how recent it is" through 2021-1947 = ?

The real Question there isn't "how recent it is". It's "Whether it's up to date" or "How up-to-date it is…"

  • Thank you for your advice. Sometimes, it's difficult for me to choose between ELU and ELL. I was afraid if my question was too basic if I asked in ELU, I thought here was safer.
    – user516076
    Oct 15, 2021 at 2:57
  • @user516076 That sounds wholly reasonable, and in many cases idiom is so much about usage, the words might almost be interchangeable… Oct 16, 2021 at 20:55

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