Many people, perhaps most, don’t know how to use hyphens with compound adjectives. It’s worth learning because use or non-use of hyphens can make a difference to how people interpret your meaning.
I remember learning about various rules of grammar in school, but I don’t think my teachers ever mentioned the use of hyphens with compound adjectives. I suspect my teachers weren’t the only ones leaving this out, because it’s so common to see writing where hyphens are needed but absent.
Perhaps it sounds like a nit-picky grammar-nerd sort of issue that people don’t really need to worry about, but in my view it is worth paying attention to. At the very least, good use of hyphens is a skill that can help make your text more readable. And in certain cases the omission of hyphens can change your meaning in serious ways.
Here are some examples where hyphens avoid ambiguity, misinterpretation, confusion or just nonsense.
A violent-weather conference is a conference about violent weather.
A violent weather conference is a conference about weather, and the conference is violent.
A small-state senator is a senator from a small state.
A small state senator is a state senator who is small.
Built-in cupboards are cupboards that are fixed into the house.
Built in cupboards describes something that was constructed within cupboards.
A first-aid post is a post that provides first aid.
A first aid post is an aid post that is, in some sense, ranked first.
What is going on? The hyphen is binding together the two words that precede the noun. When they are bound together, they apply jointly to the noun. First-aid is one thing. A small-state is one thing. These bound-together things are adjectives because they describe the following noun. (What type of senator is she? A small-state senator.) They are compound adjectives because they consist of two or more words.
If we leave the hyphen out, the two words are not bound together and the last word in the pair moves over and belongs to the noun instead. The first word in the pair remains an adjective, but it’s now on its own, describing the next two words. (What type of weather conference was it? A violent one.)
In most cases, omitting the hyphen(s) from a compound adjective doesn’t cause as much ambiguity as the above examples. However, it often does affect the reading process, as the reader has to spend at least a little bit of time working out from the context whether or not the first two words in the phrase are linked together or not. With hyphens in place, a reader can just whiz along without having to puzzle about how to interpret the words. I think it makes the process of reading more relaxing and enjoyable.
Here are some examples from academic research papers where there should have been hyphens but they were originally omitted:
If you’re excited by this stuff, you might like to know about some ifs and buts related to the use of hyphens in this way.
A compound adjective occurring after the noun don’t require a hyphen.
I have a water-proof jacket (hyphen).
My jacket is water proof (no hyphen).
Sometimes a particular pair of words can be a compound adjective in one situation (requiring a hyphen) and a noun in another situation (requiring no hyphen).
This is a long-run trend (with hyphen).
This trend will continue in the long run (no hyphen).
Multiple adjectives don’t need hyphens, only compound adjectives. In “an articulate intelligent person”, articulate and intelligent are two separate adjectives, so they don’t need a hyphen.
If the first word in the compound adjective is an adverb (skilfully, happily, stupidly), don’t use a hyphen because it’s obviously linked to the next word.
A skilfully negotiated result.
A happily married man.
A stupidly designed policy.
Finally, note that hyphens are not the only way to indicate that a set of words is a compound adjective. Here are some alternatives that you might prefer in some situations.
Quotation marks: The politician flashed his “trust me” smile.
Title Case: I found the Perth City Council building. (Often used for titles.)
Italics: It was an ad hoc decision. (Often used for foreign phrases.)
In these cases, you don’t also need to include hyphens because it is obvious that the words in quotes, title case or italics belong together.