Definition of Grammatical case

In grammar, the case of a noun or pronoun indicates its grammatical function in a greater phrase or clause; such as the role of subject, of direct object, or of possessor. While all languages distinguish cases in some fashion, it is only customary to say that a language has cases when these are codified in the morphology of its nouns — that is, when nouns change their form to reflect their case. (Such a change in form is a kind of declension, hence a kind of inflection.) Cases are related to, but distinct from, thematic roles such as agent and patient; while certain cases in each language tend to correspond to certain thematic roles, cases are a syntactic notion whereas thematic roles are a semantic one.