A grammatical case is a category of nouns and noun modifiers (determiners, adjectives, participles, and numerals) that corresponds to one or more potential grammatical functions for a nominal group in a wording. In various languages, nominal groups consisting of a noun and its modifiers belong to one of a few such categories. For instance, in English, one says I see them and they see me: the nominative pronouns I/they represent the perceiver, and the accusative pronouns me/them represent the phenomenon perceived. Here, nominative and accusative are cases, that is, categories of pronouns corresponding to the functions they have in representation.
