Morphosyntactic alignment
In linguistics, morphosyntactic alignment is the grammatical relationship between arguments—specifically, between the two arguments (in English, subject and object) of transitive verbs like "the dog chased the cat", and the single argument of intransitive verbs like "the cat ran away". English has a "subject," which merges the more active argument of transitive verbs with the argument of intransitive verbs, leaving the "object" distinct; other languages may have different strategies, or, rarely, make no distinction at all. Distinctions may be made morphologically (through case and agreement), syntactically (through word order), or both. Terminology. Arguments. Dixon (1994). The following  notations will be used to discuss the various types of alignment: Note that while the labels S, A, O, and P originally stood for subject, agent, object, and patient, respectively, the concepts of S, A, and O/P are distinct both from the grammatical relations and thematic relations. In other words, an A or S need not be an agent or subject, and an O need not be a patient. In a nominative–accusative system, S and A are grouped together, contrasting O. In an ergative–absolutive system, S and O are one group and contrast with A. The English  language represents a typical nominative–accusative system ("accusative" for short). The name derived from the nominative and accusative cases. Basque is an ergative–absolutive system (or simply "absolutive"). The name stemmed from the ergative and absolutive cases. S is said to align with either A (as in English) or O (as in Basque) when they take the same form. Bickel & Nichols (2009). Listed below are argument roles used by Bickel and Nichols for the description of alignment types. Their taxonomy is based on semantic roles and valency (the number of arguments controlled by a predicate). Locus of marking. The term  locus refers to a location where the morphosyntactic marker reflecting the syntactic relations is situated. The markers may be located on the head of a phrase, a dependent, and both or none of them. Types of alignment. The direct, tripartite, and transitive alignment types are all quite rare. The alignment types other than Austronesian and Active-Stative can be shown graphically like this: In addition, in some languages, both nominative–accusative and ergative–absolutive systems may be used, split between different grammatical contexts, called split ergativity. The split may sometimes be linked to animacy, as in many Australian Aboriginal languages , or to aspect, as in Hindustani and Mayan languages. A few Australian languages, such as Diyari, are split among accusative, ergative, and tripartite alignment, depending on animacy. A popular idea, introduced in Anderson (1976), is that some constructions universally favor accusative alignment while others are more flexible. In general, behavioral constructions (control, raising, relativization) are claimed to favor nominative–accusative alignment while coding constructions (especially case constructions) do not show any alignment preferences. This idea underlies early notions of ‘deep’ vs. ‘surface’ (or ‘syntactic’ vs. ‘morphological’) ergativity (e.g. Comrie 1978; Dixon 1994): many languages have surface ergativity only (ergative alignments  only in their coding constructions, like case or agreement) but not in their behavioral constructions or at least not in all of them. Languages with deep ergativity (with ergative alignment in behavioral constructions) appear to be less common. Comparison between ergative-absolutive and nominative-accusative. The arguments can be symbolized as follows: The S/A/O terminology avoids the use of terms like "subject" and "object", which are not stable concepts from language to language. Moreover, it avoids the terms "agent" and "patient", which are semantic roles that do not correspond consistently to particular arguments. For instance, the A might  be an experiencer or a source, semantically, not just an agent. The relationship between ergative and accusative systems can be schematically represented as the following: The following Basque examples demonstrate ergative–absolutive case marking system: In Basque, "gizona" is "the man" and "mutila" is "the boy". In a sentence like "mutila gizonak ikusi du", you know who is seeing whom because "-k" is added to the one doing the seeing. So the sentence means "the man saw the boy". If you want to say "the boy saw the man", add the "-k" instead to the word meaning "the boy": "mutilak  gizona ikusi du". With a verb like "etorri", "come", there's no need to distinguish "who is doing the coming", so no "-k" is added. "The boy came" is "mutila etorri da". Japanese – by contrast – marks nouns by following them with different particles which indicate their function in the sentence: In this language, in the sentence "the man saw the child", the one doing the seeing ("man") may be marked with "ga", which works like Basque "-k" (and the one who is being seen may be marked with "o"). However, in sentences like "the child arrived" "ga" can still be  used even though the situation involves only a "doer" and not a "done-to". This is unlike Basque, where "-k" is completely forbidden in such sentences.