When should phrases of more than two words be hyphenated, and when should the constituent words stand on their own? The following sentences, and the discussions and revisions that follow each, illustrate the rules pertaining to hyphenation of phrases.
1. The researchers highlighted the follow the herd mentality the students exhibited.
Because the phrase “follow the herd” constitutes one idea modifying the word mentality—and precedes the noun—the phrase should be hyphenated: “The researchers highlighted the follow-the-herd mentality the students exhibited.” (In the following sentence, “follow the herd” does not modify anything—it’s simply a verb phrase—so hyphens are not called for: “The students appeared to follow the herd in their everyday behavior.”)
2. The committee thoroughly reviewed the potential conflicts-of-interest before making a decision.
Here, a phrase is hyphenated unnecessarily. “Conflicts of interest” is simply a noun phrase; it does not collectively modify anything, so no linking of the words is necessary: “The committee thoroughly reviewed the potential conflicts of interest before making a decision.” (If the phrase modified, and preceded, a noun—with a slight change to singular form for the first word— hyphenation would be correct, as in, “The conflict-of-interest implications are troublesome.”)
3. The agency’s structure violates the constitutional separation of powers doctrine.
Here, a noun phrase in the “(blank) of (blank)” form serves to modify a noun, thus transforming to a phrasal adjective. Because the three words combine to form an idea and precede the noun they refer to, they should be hyphenated: “The agency’s structure violates the constitutional separation-of-powers doctrine.” (Constitutional modifies but is not part of the modifying phrase, so it is not attached.)
4. Her manager was none-too-pleased to see her arriving late for the second time in one week.
This idiomatic phrase represents a single idea, but because it does not immediately precede the noun it applies to, hyphenation is not appropriate: “Her manager was none too pleased to see her arriving late for the second time in one week.” (However, it should be hyphenated in a sentence such as “Her none-too-pleased manager watched her arrive late for the second time in one week,” because the phrase “none too pleased” precedes the noun it modifies.)
5. We apparently will be informed on a need to know basis.
Here, “need to know,” which, if it were to stand alone (as in “You don’t need to know”), would not require hyphens, merits them because the words together describe the type of basis in question, so the phrase serves as a phrasal adjective: “We apparently will be informed on a need-to-know basis.”