In linguistics,the Modal case is a grammatical case used to express ability, intention, necessity, obligation, permission, possibility, etc. It takes the place of English modal verbs such as can, could, would, might, may. Linguistics is the scientific study of language. ... In grammar, the case of a noun or pronoun is its grammatical function in a greater phrase or clause; such as the role of subject, of direct object, or of possessor. ... A modal verb (also modal, modal auxiliary verb, modal auxiliary) is a type of auxiliary verb that is used to indicate modality. ...
This case can be found in the Kayardild language and the other Tangkic languages of Northern Australia.
Nominative-accusative (or simply accusative): The argument (subject) of an intransitive verb is in the same case as the agent (subject) of a transitive verb; this case is then called the nominative case, with the patient (direct object) of a transitive verb being in the accusative case.
Ergative-accusative (or tripartite): The argument (subject) of an intransitive verb is in its own case (the intransitive case), separate from that of the agent (subject) or patient (direct object) of a transitive verb (which is in the ergative case or accusative case, respectively).
The Status of Morphological Case in the Icelandic Lexicon by EirĂkur Rögnvaldsson.