Absolutive case
The absolutive case (abbreviated ABS) is the unmarked grammatical case of a core argument of a verb (generally other than the nominative) that is used as the citation form of a noun.
In ergative–absolutive languages
In ergative–absolutive languages, the absolutive is the case used to mark both the subject of an intransitive verb and the object of a transitive verb in addition to being used for the citation form of a noun. It contrasts with the marked ergative case, which marks the subject of a transitive verb.
For example, in Basque the noun mutil ("boy") takes the bare singular article -a both as the subject of the intransitive clause mutila etorri da ("the boy came") and as the object of the transitive clause Irakasleak mutila ikusi du ("the teacher has seen the boy") in which the subject bears the ergative ending -a-k.
In a very few cases, a marked absolutive has been reported, including in Nias and Sochiapam Chinantec.
In nominative–absolutive languages
In nominative–absolutive languages, also called marked-nominative languages, the nominative has a case inflection, and it is the accusative and citation form that are unmarked. The unmarked accusative/citation form may be called absolutive to clarify that the citation form is used for the accusative case role rather than for the nominative, as it is in most nominative–accusative languages.
In tripartite languages
In tripartite languages, both the agent and object of a transitive clause have case forms, ergative and accusative, and the agent of an intransitive clause is the unmarked citation form. It is occasionally called the intransitive case, but absolutive is also used and is perhaps more accurate since it is not limited to core agents of intransitive verbs.
In nominative–accusative languages
In nominative–accusative languages, both core cases may be marked, but often, it is only the accusative that is marked. In such situations, the term 'absolutive' could aptly describe the nominative, but the term is seldom used that way.