Linguistic typology

Languages are categorized into several case systems, based on their morphosyntactic alignment — how they group verb agents and patients into cases:

§  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 thenominative case, with the patient (direct object) of a transitive verb being in the accusative case.

§  Ergative–absolutive (or simply ergative): The argument (subject) of an intransitive verb is in the same case as the patient (direct object) of a transitive verb; this case is then called theabsolutive case, with the agent (subject) of a transitive verb being in the ergative 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).

§  Active–stative (or simply active): The argument (subject) of an intransitive verb can be in one of two cases; if the argument is an agent, as in "He ate," then it is in the same case as the agent (subject) of a transitive verb (sometimes called the agentive case), and if it's a patient, as in "He tripped," then it is in the same case as the patient (direct object) of a transitive verb (sometimes called the patientive case).

§  Trigger: One noun in a sentence is the topic or focus. This noun is in the trigger case, and information elsewhere in the sentence (for example a verb affix in Tagalog) specifies the role of the trigger. The trigger may be identified as the agent, patient, etc. Other nouns may be inflected for case, but the inflections are overloaded; for example, in Tagalog, the subject and object of a verb are both expressed in the genitive case when they are not in the trigger case.

The following are systems that some languages use to mark case instead of, or in addition to, declension:

§  Positional: Nouns are not inflected for case; the position of a noun in the sentence expresses its case.

§  Adpositional: Nouns are accompanied by words that mark case.

Some languages have very many cases; for example, a Northeast Caucasian language, Tsez can be analyzed as having 128 - 64 for singular and 64 for plural, with a few exceptions.

With a few exceptions, most languages in the Finno-Ugric group make extensive use of cases. Finnish has 15 cases according to the traditional understanding (or up to 30 depending on the interpretation). However, only 10 are commonly used in speech (see Finnish noun cases). Estonian has 14 and Hungarian has 18.

John Quijada's constructed language Ithkuil has 81 noun cases, and its descendent Ilaksh has a total of 96 noun cases.

The lemma form of words, which is the form chosen by convention as the canonical form of a word, is usually the most unmarked or basic case, which is typically the nominative, trigger, or absolutive case, whichever a language may have.