An Appositive is a noun or phrase that comes after another noun (or pronoun), and identifies, explains or gives more information about that word.

If the Appositive is needed to identify the noun (called Restrictive Appositive) then no comma is used.

If the Appositive provides only additional, accompanying information about the noun – it is called Nonrestrictive Appositive and it should be set off from the rest of the sentence with commas (dashes, colons and parentheses can also be used).

In the following examples, appositives shown in color and the nouns they modify is underlined.

  • Moscow, the capital of Russia, is a crowded city.
  • Peter’s father, Mr. Smith, helped me with my homework.
  • My brother, Sasha, is the best person in a world.
  • Peter’s sister Sandy left the room.

Appositives in the first three sentences are nonrestrictive. They are not essential to the meaning of the sentence. Peter has only one father and I have only one brother. But, in the last sentence, since Peter has more than one sister, the name Sandy is necessary to identify which sister is being discussed. That is why punctuation is not used in last sentence. Looking from different perspective, since no punctuation surrounds the appositive Sandy, we know that Peter has more than one sister.