An appositive phrase is a noun or pronoun with a modifier. It is placed immediately before or immediately after a noun or pronoun that it renames or identifies.
- Bobby, his twin brother, is hours older than he.
(The appositive phrase his twin brother follows the noun Bobby that it identifies.)
- A head chef in a London hotel, George is the only son in a family of five daughters.
(The appositive phrase a head chef in a London hotel precedes the noun George that it modifies.)
In identifying a noun in a sentence, an appositive phrase is providing more information about the noun. The information may or may not be essential to the meaning of the sentence. When the information is essential, no commas are used to set off the appositive phrase. If the information is nonessential, commas are used before and after the appositive phrase, as the sentence is complete and clear without it.
- The famous singer Carole King is an American composer and singer-songwriter.
(No commas are used to enclose the appositive Carole King as the information is essential. Without the appositive Carole King, there would be no idea which famous singer is being referred to: The famous singer is an American composer and singer-songwriter.)
- Carole King, the famous singer, is an American composer and singer-songwriter.
(Commas are used to enclose the appositive phrase the famous singer as the information is not essential. Without the appositive phrase, the sentence is clear as to who the subject Carole King is.)