One of the most frequent style errors among writers is the omission of one or more hyphens in a phrasal adjective, a phrase consisting of two or more words linked to show that they’re teaming up to modify a noun that follows them. There’s an easy test to help you see that the hyphen is necessary.
When you write a phrase consisting of a noun preceded by two words describing the noun, confirm that the first and second word together modify the third, rather than that the second and third words constitute a compound noun modified by the first word. In the following sentence, for example, the latter holds true: “Indeed, the agency grants authority for community prevention efforts.” Here, “prevention efforts” is an open compound noun modified by community — the sentence does not refer to efforts to prevent community — so no hyphen is required.
Also, note that not every phrasal adjective requires a hyphen. Many open compound nouns (for example, “high school,” “income tax,” and “real estate”) are so well established that they appear in dictionaries as terms in their own right and do not require hyphenation when they are converted into adjectives to modify a noun (for example, “high school student,” “income tax form,” and “real estate agent”).
In a given sentence with a modified noun, ask yourself what kind of thing is being described, then hyphenate accordingly:
1. “This foundation has a feel good name.”
What kind of a name does it have? One designed to make you feel good, not a good name that feels. So, it’s a feel-good name: “This foundation has a feel-good name.”
2. “The small Victorian beach town lifted a decades old ban.”
What kind of a ban is it? One that has lasted for decades, not an old ban that is decades. So, it’s a decades-old ban: “The small Victorian beach town lifted a decades-old ban.”
3. “A truck and a car collided, triggering a seven vehicle crash.”
What kind of crash was it? One involving seven vehicles, not a vehicle crash that is seven. So, it’s a seven-vehicle crash: “A truck and a car collided, triggering a seven-vehicle crash.”
4. “It’s the Bay Area’s fastest growing town.”
What kind of town is it? One that is growing faster than any other, not a growing town that’s fastest. So, it’s the fastest-growing town: “It’s the Bay Area’s fastest-growing town.”
5. “The bumps have been causing two hour delays.”
What kind of delays are they? Ones lasting two hours, not hour delays that are two. So, they’re two-hour delays: “The bumps have been causing two-hour delays.”