The label appositive refers to a noun phrase which immediately follows another noun phrase of identical reference. An appositive is usually non-restrictive which means that it only gives additional information about the first noun phrase whose reference in quite clear. In writing a non-restrictive appositive is set off by commas. The phrases set off by commas in the following sentences are examples of non-restrictive appositives.
- Mexico City, the largest city in the Americas, is heavily polluted. (Here the noun phrase ‘the largest city in the Americas’ is used in apposition to the noun phrase ‘Mexico City’.)
- Alice, my neighbour, has seven cats.
- Tagore, the great poet, is the first Asian to win the Nobel Prize for literature.
An appositive can be easily removed from a sentence without leaving behind anything ungrammatical. The sentence ‘Alice has seven cats’, for example, is both grammatical and sensible. An appositive can also be restrictive, although it is not very common. A restrictive appositive is required for the identification of the reference of the first noun phrase. A restrictive appositive is not set off by commas in writing. An example is Tagore in the sentence ‘I am writing a biography of the poet Tagore’. Here removing Tagore will make it impossible to interpret the meaning of the sentence.