The function of the case system is to mark the relation between dependent nouns and their heads. Traditionally, the term case has referred to declension. Case typically serves to mark the relationship of the noun to the verb at the sentence level, or to an adposition or other noun at the phrase level.[1] The number of nominal cases in a language is measured in terms of productive paradigms of prototypical nouns.

Types:

NoNCase: The language does not have a case system.

2NCases: The case system has two cases.[2]

XNCases: The case system has x number of cases.

[1] Cases are identified primarily based on their form. If a language uses the same form to express two or more distinct case functions, that form is considered a single, multifunctional case. As long as they do not mark a regular semantic distinction, allomorphic and facultative variants do not count as cases. Forms that express non-syntactic functions, such as topicalization and the vocative, do not constitute cases. Genitive forms may constitute a case if they do not display the formal behavior of adjectives (such as showing number and gender agreement with the possessed). In the event that a noun is marked by multiple cases, each case is counted individually. Cases that carry a derivational function are considered to be derivational morphemes.

[2] The minimum number of possible cases is two. If a case distinction exists, the unmarked member of the paradigm is also considered a case.