Day 84: Use a comma to set off appositives.

An appositive is a word or phrase that provides non-essential information (i.e., not required to make the sentence grammatically correct) and that renames a previous word. Consider this sentence.

“The automobile, a great invention, provides mobility to many people.”

The phrase “a great invention” is not necessary to the idea of the sentence, “The automobile provides mobility to many people,” and it renames or describes “the automobile.” Here’s another example:

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“Fred put on his scarf, a long, flowing snake-like thing.”

In this example, “a long, flowing, snake-like thing” is not essential to understanding Fred’s action, and it renames or describes “scarf.”

As you can see from the examples, appositives are set off from the rest of the sentence by commas. In the first example, we used commas before and after the appositive. In the second example, we only needed a comma before the appositive because the sentence ends with a period after the appositive.