In grammar, the vocative case (abbreviated ) is a grammatical case which is used for a noun that identifies a person (animal, object, etc.) being addressed, or occasionally for the noun modifiers (determiners, adjectives, participles, and numerals) of that noun; the comma that should be applied in such a context is referred to as a vocative comma. The usage of vocative case in the English language (and many others where commas are used) necessitates a comma to help clarify the writer's intent; failure to strictly adhere to this rule can lead to confusion over the writer's intent. A vocative expression is an expression of direct address by which the identity of the party spoken to is set forth expressly within a sentence. For example, in the sentence "I don't know, John," John is a vocative expression that indicates the party being addressed, as opposed to the sentence "I don't know John" in which "John" is the direct object of the verb "know". In simple terms, the first sentence is the speaker telling a person called John that they do not know something, while the second sentence is the speaker saying that they do not know who John is. A well-known humorous example is "Let's eat, Grandma" and "Let's eat Grandma", where the former example is the speaker telling their grandma to eat something, while the latter example is the speaker asking a third party to join them in cannibalizing their grandmother. Historically, the vocative case was an element of the Indo-European case system and existed in Latin, Sanskrit and Greek. Many modern Indo-European languages (English, Spanish, etc.) have lost the vocative case, but others retain it, including the Baltic languages, some Celtic languages and most Slavic languages. Some linguists, such as Albert Thumb,(de) argue that the vocative form is not a case but a special form of nouns not belonging to any case, as vocative expressions are not related syntactically to other words in sentences. Pronouns usually lack vocative forms. Indo-European languages Comparison Distinct vocative forms are assumed to have existed in all early Indo-European languages and survive in some. Here is, for example, the Indo-European word for "wolf" in various languages: The elements separated with hyphens denote the stem, the so-called thematic vowel of the case and the actual suffix. In Latin, for example, the nominative case is lupus and the vocative case is lupe, but the accusative case