Morphosyntactic alignment
Morphosyntactic alignment is a term for the way that the arguments of transitive and intransitive verbs are marked in the sentences of some language. In this regard, most languages can be classified as either nominative-accusative or ergative-absolutive.
Syntactic roles
In most languages throughout the world, simple sentences usually contain a verb that describes an action or relation, and one or more nouns that are its arguments - entities involved in that action or relation. In sentences with one or two arguments, these can be classified into three syntactic roles, that we may call S, A and P:
Accusative and ergative languages differ as to how they mark those syntactic arguments.
Nominative-accusative languages group S and A, and leave P aside. If there exists morphological case marking, then S and A are both marked with a case conventionally known as "nominative", while P is marked with a case called "accusative". If there's no case marking, the language can resort to word order (for example, S and A come before the verb, while P comes after it).
Ergative-absolutive languages group S and P, and leave A aside. Either they resort to word order (as above), or they mark A with the ergative case, while S and P are marked with the absolutive case.
See the articles about accusative and ergative languages for less technical explanations and examples.
See also:
