Hyphens seem to cause a lot of distress. One of my clients asks me to look at advertising copy, and I can sure see why they’re such a problem. Let’s take a little stroll through Hyphenland and see if the whole situation can be simplified. Here’s the rule:
Place a hyphen when you want to connect two words and make them into one word.
That’s a basic rule. It means that you’d use a hyphen to:
Numbers pretty much always get hyphens, no matter how they’re used in a sentence (or while writing a check). Use a hyphen only between the “tens” and the “ones,” so you’d have six hundred twenty-seven daffodils and three thousand four hundred forty-five dust particles. Notice that there’s no “and” between the hundreds and the “tens.” If there were, it might not be clear that the spelled-out version is one big number. Most publishing entities have you use numerals for numbers greater than ten, though, so except for writing a check, you won’t have much use for this tidbit. (It's numbers greated than 20 in fiction, by the way.)
Use a hyphen to make clear the difference between the quantity and the measurement of something if you would have used a hyphen to describe the thing anyway. If you were going to talk about a four-foot pole, you’d say 10 four-foot poles or ten 4-foot poles.
There are some words that might one day become a single word but still use hyphens to connect them, like merry-go-round, reporter-at-large, or stand-alone. As you can see from my examples, these are not always nouns.
Here’s the tricky one: attaching an adjective to another adjective or a noun. A good rule of thumb is to try “skipping” the second descriptive word to see if it still makes sense. If you can skip that word, you don’t need a hyphen.
He is a well-rounded person.
He is a well person.
If you skip the word “rounded,” you’re talking about the fellow’s bulk instead of his education or brilliant mind. Let’s try it another way:
He is a well rounded-person.
He is a well rounded person.
Both of these sentences mean that he is influenced by a well. In the first one, the well has caused his roundness and a rounded-person is some specific type of person. In the second example, if you drop the “rounded,” you’re back to saying that he is a “well person,” which I suppose could mean he’s healthy if you look at the previous example, or it could mean that he belongs to a secret society of well fanciers. Or maybe that he lives in a well. The reason you want a hyphen here is because “well-rounded” is a compound modifier before the noun. The noun is “person” and the modifying adjective and adverb set is compound because neither word makes a lot of sense on its own in this context. You really have to link them with a hyphen.
If you move the noun away, you don’t need a hyphen because the adverb and adjective don’t modify the noun anymore (because you moved it or got rid of it).
The person is well rounded.
He is well rounded.
In this case, there is no way to separate the words. The person is rounded. How is he rounded? He is rounded well. There is no way to misinterpret the meaning, so you don’t need the hyphen to link anymore.
There’s one little exception to this rule, and that’s if the adverb ends in “ly.” Words with "ly" never get hyphens. I did not make this rule, so don’t yell at me. In my head, an adverb is an adverb, whether it ends in “ly” or not. But there’s this rule anyway.
The teenager was badly-acne scarred.
That’s wrong, for two reasons. One is that you don’t link an “ly” word to a noun or an adjective, and the other is that “acne” modifies “scarred.” So the sentence should be:
The teenager was badly acne-scarred.
Let’s look at another one.
This is a badly punctured basketball.
This is a well-loved teddy bear.
In the second sentence, you can see the need for the hyphen—you can’t say “This is a well teddy bear,” after all. The only thing that makes this usage different from the first one in that pair is the “ly” ending on the word “bad.” The first sentence doesn’t get a hyphen anywhere.
You also don’t use a hyphen between parts of a proper noun. Where you’d say:
The American economy was affected by last year’s drought.
You’d also say:
The North American economy was affected by last year’s drought.
Even though strictly speaking, “North” modifies “American,” it’s a proper noun, so it doesn’t get a hyphen.
In other news, use a hyphen to separate a prefix from the rest of the word if the vowel is repeated or the meaning would be obscured. Consider re-elect and reelect, co-op and coop, re-sign and resign, re-form and reform, re-sent and resent.
Finally, when your document or line of programming doesn’t have the convenience of word wrapping to spread characters evenly across the page, use a hyphen to separate one syllable from another. That means you can’t break up monosyllabic words, and that you need to KNOW where the syllables end (“syllable” breaks up to be syl-la-ble, for instance, right between the Ls). Knowing where to break a word may require a trip to the dictionary.