Grammarama

Compound Modifiers

When two words act together as an adjective to modify a noun, a hyphen is often used to join them:

This book has color-coded pages.
Are you ready for a fun-filled day?
That was an action-packed movie.
I am a law-abiding citizen.

In the above cases, omitting the hyphen may cause minor confusion, but at other times, the meaning of the sentence can become totally unclear:

I saw a man eating tiger today.

If what you mean is that you saw a human eating tiger meat, then this is right; but if you mean to say you saw a tiger who eats humans, then “man-eating” should be hyphenated. Since I don’t know of any societies in which tiger meat is a delicacy, it can probably be safely assumed that this sentence refers to the latter, but this example shows how hyphens can greatly affect understanding.

If the compound modifiers in the above sentences come after the noun they’re modifying, they don’t need to be hyphenated:

This book has pages that are color coded.
Are you ready for a day that’s fun filled?
That movie was action packed.
I am a citizen who is law abiding.

But the sentences can also be written in different – sometimes better – ways by rearranging the words of the compound modifiers:

This book’s pages are coded by color.
Are you ready for a day full of fun?
That movie was packed with action.
I am a citizen who abides by the law.

As explained below, there are exceptions to the rule of hyphenating compound modifiers.

Exception 1: Don’t hyphenate if both elements of the compound modifier are nouns.

The ice cream truck is here!
John Travolta starred in Saturday Night Fever.

These sentences are easily understood without hyphens.

Exception 2: Don’t hyphenate if the first element of the compound modifier is an adverb ending in –ly.

That was an incredibly long movie.
Some people think Kias are poorly made cars.

In the following case, “fast” serves as an adverb, but it’s not an adverb ending in –ly. Because “fast” can also act as an adjective in some cases, hyphenation is beneficial to understanding:

Fast-acting inhalers are also called rescue inhalers.

Exception 3: Don’t hyphenate if the first element of the compound modifier is a comparative or superlative adjective.

She is in middle school and already taking higher level math courses.
He is not the most popular kid in school.

Exception 4: Don’t hyphenate if the second element of the compound modifier is just a letter.

I bought some Grade A eggs today.
People with type B personalities are usually calm and relaxed.