Commas with Nonessential Elements
This resource offers a number of pages about comma use.
Contributors:Dana Driscoll, Allen Brizee
Last Edited: 2011-05-10 04:18:44
Some modifying elements of a sentence are essential, restricting the meaning of a modified term, while others are nonessential and don't restrict the modified term's meaning. These nonessential elements, which can be words, phrases, or clauses, are set off with commas.
Rule: Use commas before and after nonessential words, phrases, and clauses, that is, elements embedded in the sentence that interrupt it without changing the essential meaning.
Deciding whether an element is essential or nonessential can sometimes be tricky. For help identifying two common types of phrases that can be either essential or nonessential, see the OWL handouts on verbals, which includes information on participial phrases, as well as the handout on appositives, which covers appositive phrases. Both of these documents address the essential/nonessential distinction for these kinds of phrases.
You can try three different interactive exercises that allow you to practice these rules, each with its own answer key.