Vocative expression

In linguistics, a vocative or vocative expression is a phrase used to identify the addressee of an utterance. The underlined phrases in each of the following English sentences are examples of vocatives:

Sir, your table is ready.

I'm afraid, Mr. Renault, that your card has been declined.

Quit playing around, bozo.

Syntactically, vocatives are noun phrases which are isolated from the structure of their containing sentence, not being a dependent of the verb. In some languages, vocatives are marked morphologically with a particular grammatical case, the vocative case. English lacks a vocative case, but sets vocatives off from their containing sentence in speech by a particular intonational pattern, and in writing by the use of commas.^[1]