Declension

• Nominative-accusative: The agent of a verb is always in the nominative case, along with the patient of intransitive verbs. If both agent and patient are present, the patient 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 inf ormation 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.

• 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.

• Declension in English
• Slovak declension
• Latin declension

• Scene 8, Monty Python's the Life of Brian explains Latin declension. Best if viewed in the context of the movie before reading.
• The Status of Morphological Case in the Icelandic Lexicon by Eiríkur Rögnvaldsson. Discussion of whether cases convey any inherent syntactic or semantic meaning.
• Optimal Case: The Distribution of Case in German and Icelandic by Dieter Wunderlich