Use Commas Before Nonrestrictive Adverbial Phrases or Clauses at the Ends of Sentences

At the end of your sentence, you need to be especially careful about where you place your commas. In particular, you need to question whether the modifying words are restrictive or nonrestrictive. For instance, suppose you received a memo from your writing instructor that said,

  • You should revise the essay, as I suggested.

You could assume that you were directed to revise the essay in any way you deem appropriate. However, if the instructor omitted the comma, then you would be receiving an entirely different message: revise the essay exactly as prescribed by the instructor.

Below are some additional sentences to give you a sense of how to determine whether your modifying words are restrictive or nonrestrictive:

  • Nonrestrictive: Reports indicate that a Turtle Excluder Device (TED) costs from $85 to $400, depending on the model.
  • Restrictive: Writers can change readers’ outlooks on issues provided that they offer sufficient evidence.

In this case, a comma after issues could suggest that writers have numerous ways to change readers’ opinions and that one of these methods is providing sufficient evidence. In contrast, the lack of a comma means that providing evidence is the one criterion writers need to follow.

Other comma resources: