In linguistics, declension is a feature of inflected languages: generally, the alteration of a noun to indicate its grammatical role.
In inflected languages, nouns are said to decline into different forms, or morphological cases. Morphological cases are one way of indicating grammatical case; other ways are listed below.
This is seen, for example, in Latin, Russian, and many other languages. Old English had an extensive case system. In modern English grammar, the same information is now mostly conveyed with word order and prepositions, though a few remnants of the older declined form of English still exist (e.g., the words "who" and "whom"; see Declension in English).
Languages are categorized into several case systems, based on how they group verb agents and patients into cases:
- Nominative-accusative: The agent of both transitive and intransitive verbs is always in the nominative case. The patient of a (transitive) verb is in the accusative case. The dative case may also be present.
- Ergative-absolutive: The patient of a verb is always in the absolutive case, along with the agent of intransitive verbs. If both agent and patient are present, the agent is in the ergative case.
- Active: The agent of a verb is always in the subject case, and the patient is always in the object case. The case does not depend on whether a verb is used in a transitive or intransitive form.
- Trigger: One noun in a sentence is the topic or focus. This noun is in the trigger case, and information elsewhere in the sentence (e.g. 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.
- Prepositional/postpositional: Nouns are accompanied by words that mark case, but the noun itself is not modified.
Some languages have more than 20 cases. For an example of a language that uses a large number of cases, see Finnish language noun cases.
Chinese, Korean have systems similar to declension whereby different counting words are used when counting different classes of nouns, e.g. persons, animals, things, cylindrical objects, flat objects, etc.
- Scene 8, Monty Python's the Life of Brian (http://www.mwscomp.com/movies/brian/brian-08.htm) explains Latin declension. Best if viewed in the context of the movie before reading.
- The Status of Morphological Case in the Icelandic Lexicon (http://www.hi.is/~eirikur/cases.pdf) by Eiríkur Rögnvaldsson. Discussion of whether cases convey any inherent syntactic or semantic meaning.
- Optimal Case: The Distribution of Case in German and Icelandic (http://web.phil_fak.uni_duesseldorf.de/~wdl/OptCase.pdf) by Dieter Wunderlich