The Problem with Idioms
Cut to the chase, face the music, and get over it. These are all idioms. If you are not a native English speaker, you may have spent numerous hours trying to memorize idioms because they are so important in conversation. If you are a native American English speaker, you may have no idea what I'm talking about. These aren't idioms, they're just things we say all the time. If you look at the words in these phrases and consider their literal meaning, it doesn't make a lot of sense.
Idioms are phrases and expressions that we use all the time in spoken language, but that should be avoided in written language. A lot of times, we don't even realize we are using them because they are such a normal part of our speech. They help us fill conversational voids and give us something to say when we don't know what else to say. Some of them are obvious (shooting fish in a barrel), and some of them are so common we don't even recognize them as idioms (hidden in plain sight).
1. One problem is that they are used so often, they often don't have as much meaning as we think they do.
They're really just handy expressions, something to say. Consider this: "Tuition at public universities now costs an arm and a leg."
That's an idiom you may hear a lot, depending on where you're from. In Texas, people say it all the time. But what does the expression mean? Expensive, right? Well, that really depends on who says it. The truth is, the expression just communicates that the tuition is expensive for the speaker. If I'm talking to my friend, and she makes that statement, I understand what she means because I know her socioeconomic group and what she can afford. In other words, I know her reference points. The tuition might be the expensive for me, too, or it might not be. But the point is, I know enough about the speaker that I can make that determination.
Always assume when you're writing (especially in academic writing) that your reader is a total stranger. They don't know anything about you. Maybe you're a middle class American, and an "arm and a leg" is $25,000 a year. Maybe you live on minimum wage, and to you an "arm and a leg" is $8,000 a year tuition. Perhaps your father is an oil tycoon, you inherited a lot of money, and what you consider expensive tuition would be more like $70,000 a year. This is why you need to be more precise when you're writing.
Here's a new sentence:
"Tuition at public universities now costs about $24,000 a year, almost half of the median income in the United States."
My new sentence has given an exact number, which makes me (the writer) seem more knowledgeable. Now, rather than describing this cost of tuition in terms of my own economic situation (which you don't necessarily share), I've described it in terms that most people can understand. There is a solid, universal reference point.
2. Idioms are often specific to a certain dialect or region.
I know the difference in intensity between a sun shower and a regular toad-strangler. If my grandmother had told me she was going to show me how the cow ate the cabbage, I would have straightened up immediately. If my mom had said she was going to skin my hide, nobody in our neighborhood would have called the police. But that's because I grew up in Texas. If you don't live in Texas, or even if you don't live in rural Texas, you probably have no idea what some of those expressions mean. Don't assume your reader comes from the same place as you. Idioms can differ between regions, dialects, age groups and even socio-economic classes. When you're writing an argumentative or a research paper, it's important that you try to appeal to everyone by using the standard form of language (in this case, standard English). Using dialect or regional idioms excludes a lot of people, including people in your community who may be transplants from other regions or who don't speak English as their first language.
3. Your reader might take your idiom seriously.
"A pill that can help bald men regrow their hair? I don't buy it."
The second sentence can be read two ways. The first is as an idiom that means "I don't believe it." The other way to read it is literally: "I don't purchase it (the pill that helps bald men regrow their hair)." This third point goes along with the second one, but it's also important to point out that idioms like these (as opposed to a regular toad-strangler) hide in the text. They aren't obvious. The toad-strangler is more obviously an idiom, but its meaning is more obscure. Because "buy it" is less obvious as an idiom, its literal meaning may seem more obvious. If your reader doesn't realize the phrase is an idiom, she will read it literally; and because the literal meaning fits the text, she may not think twice about it.
4. Some idioms have dark origins
I grew up hearing the phrases cotton picking and calling a spade a spade. Neither of these phrases were used in racist contexts when I heard them, but they have racist origins. Cotton picking is a phrase used like darn, as in "I can't find the cotton picking thing!" If you think about American history and cotton plantations, though, you can probably see why many people see the phrase as racist. African Americans worked as slaves, and later as free citizens without many rights, on cotton plantations. They were considered less than human. I never thought about it when I heard older people say it because my urban upbringing was far removed from the early 20th century rural South, but cotton picking references the low status of African Americans on plantations.
Similarly, spade used to be used as a derogatory term for African Americans. So while the phrase today may mean "stating the obvious," its historical equivalent was "calling a black person black." Until recently, I had no idea that spade was ever used as a term to refer to African Americans. I've used that expression before, and of course I didn't mean anything racist by it. In my opinion, it's best not to use it. Even if the meaning has changed, it still carries a lot of historical weight. Even if it's not my intent to use an offensive expression, other people might be offended by that phrase. I think this is another good reason to avoid idioms in writing. We just don't know where they come from.