So, there are three main roles that a noun phrase can play in a clause. Namely, it can be one of these:
- the sole argument of an intransitive verb (“she walks”)
- the subject of a transitive verb (“she kicks him”)
- the object of a transitive verb (“she kicks him”)
Morphosyntactic alignment basically means, “how does this language treat the sole argument of an intransitive verb”. In English, as you see above, it is treated the same as the subject of a transitive verb. This means that English is a nominative-accusative language. It doesn’t matter that we don’t mark case on ordinary nouns any more; we use strict word order to the same effect.
Nominative-accusative alignments are the most common, cross-linguistically. The second-most common is the ergative-absolutive alignment. In an ergative-absolutive language, the sole argument of an intransitive verb is instead treated as an object (either through word order, or through inflection if the language has inflections for noun cases). So in Basque, with the nouns in the unmarked absolutive case bolded:
- Martin etorri da. (Martin has arrived.)
- Martinek Diego ikusi du. (Martin has seen Diego.)
In nominative-accusative languages, generally the least-marked case (if there are declinations) will be the nominative case (the subjects). In ergative-absolutive languages, the absolutive case (that’s the one for objects and sole arguments of intransitives) is generally instead the least-marked one.
Some languages feature split ergativity, i.e. use nominative-accusative alignments in some constructions but ergative-absolutive in others (e.g. nouns vs pronouns, or maybe depending on the verb tense or aspect…). For example, in the Mayan language Chol, ergative-absolutive alignment is used with the perfective aspect, and nominative-accusative with the imperfective.
There are some other types of morphosyntactic alignments which are less common than the two above. These include:
- Austronesian alignment: Both alignments are used, and seem to be most correctly called “agent trigger” and “patient trigger”.
- Active-stative alignment: It depends on whether the sole argument fills the semantic role of an agent in the sentence (e.g. “Mary sang”) vs a patient (e.g. “Mary was there”). Georgian is an example of an active-stative language.
- Direct alignment: Literally makes no distinction, whether via word order, inflection, or anything else. Leaves it up to listeners to figure out what, logically, is the most likely meaning. This type is very rare.
- Tripartite alignment: Has a dedicated “intransitive case” for sole arguments of intransitive verbs, rather than merging that case with subject or object case. Also rare but the Nez Perce language of the Pacific Northwest is an example.
- Transitive alignment: Merges subjects and objects into a single “transitive case”, vs an “intransitive case” used for sole arguments of intransitive verbs. One example is the Iranic language Rushani.