What is the grammatical case used for direct address?

The grammatical case used for direct address is the vocative case. This case is specifically employed in languages like Latin to indicate when a speaker is directly addressing someone or something, often used with a name or title. In Latin, the vocative form may differ from the nominative or accusative forms, depending on the declension of the noun. For example, in the phrase "O, Marcus," "Marcus" is in the vocative case, signaling that Marcus is being called upon or spoken to directly. This use is critical in communication as it clarifies who is being addressed, making the message personal and direct. This distinction is essential in languages with rich inflectional systems, such as Latin, where the endings of words change according to grammatical function.