Using a comma with an adverbial clause

A comma is required before or after an adverbial clause, depending on whether it begins or ends a sentence, and if it functions as a nonrestrictive clause. A nonrestrictive clause is not essential for the reader to understand the full meaning of the word or words that it modifies. It simply adds more information, describing but not limiting (“restricting”) what it modifies. (For more info about restrictive and nonrestrictive clauses, see my earlier post “Which hunting.”)

Look at this example:

When Charley woke up a horrible stench filled the room.

I have underlined the adverbial clause. It’s nonrestrictive in this sentence, so you should place a comma after the word up. Then readers won’t misread the sentence and think that Charley woke up a horrible stench.

For the same reason you should put a comma after the adverbial clause in this cannibalistic sentence:

When we had finished eating Robert and I left the room.

Poor Robert!


Paul Thayer
My book editing website

Which hunting

            The problems many writers have with the words that and which make copy editors inveterate which-hunters. Remember that a nonrestrictive clause is not essential for the reader to understand the full meaning of the word or words that it modifies. It simply adds more information, describing but not limiting (“restricting”) what it modifies. On the other hand, a restrictive clause contains information that is essential for the reader to understand the full meaning of the word or words that it modifies. It limits (“restricts”) what it modifies. To keep things simple, use the relative pronoun that to begin restrictive clauses and which to begin a nonrestrictive clause. Examples:

Restrictive:

He showed me the book that arrived in the mail today. [The meaning is restricted to just one book—the one that arrived in the mail today.]

Nonrestrictive:

He showed me the new Stephen King novel, which is the one I told you about yesterday. [The clause just adds more information to the sentence.]

            Also note that you can often delete the word that in many constructions: The books [that] I ordered arrived today.

Paul Thayer

Your Book Editor