Which sentence correctly uses a nonrestrictive clause with commas?

• A. The author, who wrote the best-seller, won an award.
• B. The author who wrote the best-seller won an award.
• C. The author, who wrote the best-seller won an award.
• D. The author who wrote the best-seller, won an award.

Answer: (A)

Nonrestrictive clauses add extra information about a noun and are set off by commas. Here, the phrase who wrote the best-seller describes the author but isn’t needed to identify which author is being talked about. Placing it between commas signals that this information can be removed without changing who the sentence is about: The author, who wrote the best-seller, won an award. If you take out the clause, you still have a sensible sentence: The author won an award.

The other constructions try to treat the clause as essential information, which changes the meaning and uses different punctuation rules. Without the surrounding commas, the clause becomes restrictive, narrowing down which author is meant. And a sentence that leaves out the proper comma placement either has an ungrammatical rhythm or awkwardly separates the clauses. The correct punctuation for a nonrestrictive clause is the sentence with the extra information set off by commas.