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. Typically, case marks the relationship of the noun to the verb at the sentence level, or the relationship of the noun to an adposition or other noun at the phrase level.[1] In some languages, articles can be inflected alongside nouns, and the number of cases that apply to articles may differ from that of nouns.[2] The number of article cases in a language is based primarily on the paradigm of definite articles.

Types:

NoArt: The language does not have articles.

NoArtCase: The language has articles, but no article case system.

2ArtCases: The article case system has two cases.[3]

XArtCases: The article case system has x number of cases.[4]

[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] One particular example of this is when a language does not use nominal inflection, instead marking case on the article.

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

[4] If the set of article cases is not identical to the set of nominal cases, this should be noted in the commentary.