Board Thread:Linguistics/@comment-25410520-20150118055513/@comment-28303871-20150118063414

To understand morphosyntactic alignment, you first have to understand transitivity. Transitivity is the number of arguments (nouns) the verb takes. A transitive verb has both a subject and an object, whereas an intransitive verb merely has a subject. In terms of morphosyntactic alignment, we prefer the terms agent (A), patient (O) and subject (S), because these reduce ambiguity.

In nominative-accusative languages, the S behaves like the A, while the O is different. (S = A ≠ O) S and A may both take the nominative case, while the O is the accusative, or in languages without case, the S may appear in the same syntactic slot as the A. (For example, AVO, SV.)

In ergative-absolutive languages, the S behaves like the O, while the A is different. (S = O ≠ A) The A is in the ergative case, while the S and O are in the absolutive case, or in languages without case, the S appears in the same slot as O (e.g., AVO, VS). [The following is more advanced, proceed with caution: In addition to the change in marking/word order, some languages (termed "deep ergative") may make semantic changes as well, where the basic intransitive sentence takes on a meaning more similar to nominative-accusative passive voice, instead of a typical nom-acc intransitive sentence. So "kick-PR 1ST-ABS" would be translated as "I was kicked" instead of "I kick." The equivalent of the nom-acc intransitive sentence becomes expressed as the antipassive voice.]

Tripartite is fairly simple. S, A and O are merely all marked distinctly. (S ≠ A ≠ O) Different linguists use different terms for the cases in such languages, but I call them absolutive, ergative, and accusative for S, A, and O, respectively.

If you need any further clarification, I'm happy to elaborate.