Instead of using the traditional “restrictive phrase” and “nonrestrictive phrase,” AP Style uses “essential phrase” and “nonessential phrase” to convey the distinction between the two in a more easily remembered manner.
This same underlying concept is the one that also applies to clauses,
An essential phrase is a word or group of words critical to the reader’s understanding of what the author had in mind.
A nonessential phrase provides additional information about something. While they information may be helpful to the reader’s comprehension, the reader would not be misled if the information were not to be included.
Do not set an essential phrase off from the rest of a sentence by commas. For example,
- We saw the award-winning movie “The Gladiator.”
We do not use a comma in this sentence because many movies have won awards, and without the name of the movie the reader would no know which movie the author meant.
- They ate dinner with their son Joseph.
We do not use a comma in this sentence because they may have more than daughter, so the inclusion of Julie’s name is critical if the reader to know which daughter is meant.
Do set off nonessential phrases by commas. For example,
- We saw the 2012 winner in the Academy Award competition for best picture, “Argo.”
We do use a comma in this sentence because only one movie won this award in the year 2012. The name is informative, but even without the name no other movie could be meant.
- They are dinner with their daughter Julie and her husband, David.
We do use a comma in this sentence because Julie only has one husband. If the phrase read “and her husband David,” it would suggest that she had more than one husband.
- The company chairman, Bill Gates, spoke.
We use commas to set off this phrase because only one person can be meant in this context.
- Indian corn, or maize, was harvested.
Maize provides the reader with the name of the corn, but its absence would not change the meaning of the sentence.
Do not confuse punctuation rules for nonessential clauses with the correct punctuation when a nonessential word is used as a descriptive adjective. The distinguishing clue often is the lack of an article or pronoun. For example,
- Correct: Julie and husband Jeff went shopping. Julie and her husband, Jeff, went shopping.
- Correct: Company Chairman Bill Gates made the announcement. The company chairman, Bill Gates, made the announcement.