When I teach advanced student writers, I always mention how the best nonfiction prose sticks close to idiomatic language while also avoiding clichés. That’s a tall order, for a number of reasons. For one thing, idioms and clichés sometimes overlap.
Consider, for instance, my use of “tall order” above. Idiom or cliché? I think it sits on the brink of cliché, but is ultimately idiom. What’s the difference? Both idioms and clichés consist of wording we’ve heard before, but a cliché is boring, tired, or, as style impresario William Strunk, Jr. would say, “bankrupt.” An idiom, on the other hand, makes the reader feel as if he’s sharing somehow with the writer, sharing in an understanding of how the language operates and what the idiom refers to. An idiom builds rapport; it makes the reader as glad to come upon it as the writer is to have thought of it. A cliché, by contrast, puts off the reader, who’s heard it too many times before, especially if it’s colorful, and doesn’t ever want to hear it again. “Dark night of the soul” is a good example. It’s over-used, precious, and melodramatic, to boot. It pushes the reader away.
When I try to explain the concept of an idiom to my students, I describe it as the way a native speaker writes. Nonidiomatic wording, by the same token, seems to emanate from a person who isn’t entirely literate in English. Sadly, even technically native speakers are capable of producing language that seems as if it belongs to someone who isn’t immersed in the language. When hare-brained appears as hair-brained, the writer has a bigger problem than spelling; she’s missed the humor essential to the idiom’s meaning: that a person’s behavior or thoughts seem to have proceeded from a brain the size of a rabbit’s (as opposed to the width of a hair). If toe the line is written tow the line, the spirit of the idiom is mistranslated: although toe-ing and towing are both feats, the idiom’s concept involves the finesse of the first, not the brawn of the second. When reign in substitutes for rein in, the visual of controlling a horse with reins is lost.
Speaking of idiomatic expression, cliché is a noun whose adjectival form is clichéd. To use cliché as an adjective, as in “His speech was so cliché,” is nonidiomatic. It exposes the writer as someone who hasn’t read much. Learning to write idiomatically requires lots of reading to see how the language is put together.
It also involves, to use another idiom that verges on cliché, both good news and bad. The bad news is that English, possibly more than any other known language, abounds in idioms, making English idiomatic language difficult to learn. The good news is that English, being rich in idioms, presents never-ending, lavish learning and creative opportunities for people who relish words and expressions.