I’m going to talk about compound adjectives.

This post is pure, self-satisfying pedantry; feel free to ignore, especially if you’ve moved past discussions of grammar, the internet, and the decline and fall of the English language.

What are they?

Compound adjectives are, sensibly enough, adjectives that contain more than one word. Because it’s a single adjective despite containing multiple words, the compound adjective is hyphenated to ensure the multiple words are, in fact, read as one: zero-sum game, high-stakes thriller. Note that adverb + adjective constructions are not usually hyphenated, especially when the adverb in question ends with -ly: summarily executed prisoners, formally attired guests. (There are some exceptions, this being English: well-known is actually an adverb + adjective, but it’s almost always hyphenated.)

Compound adjectives are, however, often left unhyphenated by mistake. Here is a sampling of recent tweets from a variety of sources, all of which use (and abuse) compound adjectives:

Written correctly, the compound adjectives from the above tweets are as follows: press-freedom, caption-contest, hand-drawn, most-popular, and left-handed.

Why does it matter?

To read one of the above examples literally, The Economist is making a claim of quantity, not quality—to claim the “most popular images” is to claim “more popular images than anyone else.” Of course it’s obvious what is meant, and it seems silly to nitpick about it. But incorrectly hyphenated compound adjectives often make the meaning of the sentence unclear—or, more egregiously, change the meaning altogether. There’s a significant difference, for example, between multiple-car accidents and multiple car accidents. Knowing when to hyphenate and when not to hyphenate can mean the difference between a shark-feeding frenzy (we all rush to feed the sharks) and a shark feeding frenzy (the sharks all rush to eat us).

Ultimately, clarity is what’s at stake. Non-fiction and academic writing especially depend on it, but any form of writing is sharper and more effective if the wording leaves no room for misinterpretation.