casus

Casus is a term used in linguistics and grammar to describe a grammatical category that marks the role of a noun, pronoun, or adjective in a sentence. The word is derived from Latin casus, meaning “case” or “occurrence,” and in traditional Latin grammars it referred to the morphological forms of a noun that indicate its syntactic function. In languages with inflected nouns, cases are typically expressed by distinct endings, by separate words, or by a combination of both. Some languages have many cases; others rely more on word order or prepositions.

Common cases include the nominative for the subject of a sentence; the accusative for the direct object; the genitive for possession or partitive relationships; the dative for an indirect object; and the ablative for means, accompaniment, or instrument. The vocative serves for direct address. Some languages also feature locative (location) or instrumental (means) as distinct cases, and several languages differentiate several oblique cases.

In practice, cases are marked through noun, pronoun, and adjective inflection, often with agreement within a noun phrase. When inflection is limited, prepositions or syntactic position convey the function. Pronoun systems frequently preserve more case contrasts than nouns in analytic languages.

Example in Latin: servus (nom.), servum (acc.), servi (gen.), servo (dat./abl.), serve (voc.); a sentence like Servus puellam amat illustrates nominative subject and accusative object.

Casus interact with syntax and morphology to express grammatical relations, and the presence and type of cases vary widely across languages. See also: grammatical case, nominative case, genitive case, dative case.