Editing Nominative–accusative alignment (section)

===Optimality theory===
	One of the ways in which the production of a nominative–accusative case marking system can be explained is from an [[Optimality Theory|Optimality Theoretic]] perspective. Case marking is said to fulfill two functions, or constraints: an identifying function and a distinguishing function.<ref name=hoopALM>de Hoop, Helen and Malchukov, Andrej L. (2008) "Case-marking strategies". ''Linguistic Inquiry''.</ref> The identifying function is exemplified when case morphology encodes (identifies) specific [[semantics|semantic]], thematic, or [[pragmatics|pragmatic]] properties or information about the nominal argument. Accusative case in the position of the direct object, for example, can be a strong identifier of [[patient (grammar)|patienthood]]. The distinguishing function is used to distinguish between the core arguments, the subject and the object, of a transitive clause. [[Helen de Hoop]] and [[Andrej Malchukov]] explain the motivation and need for the distinguishing function in "Case marking strategies":
{{blockquote|When a two-place predicate R(x,y) is used to describe an event involving two participants, usually an agent and a patient, it is of utmost importance to avoid ambiguity as  to which noun phrase corresponds to the first argument  x  (the agent) and which to the second argument  y (the patient). For this purpose, case can be used to mark one of the arguments. If one argument is case marked, this already suffices for the purpose of disambiguation. Thus, from the distinguishing perspective, there is no need to case mark both arguments. Neither would it be necessary to case mark the one and only argument of a one-place (intransitive) predicate. Indeed, it has been argued that in many nominative–accusative case systems only the y is case marked (with accusative case) while the x  remains morphologically unmarked.<ref name=hoopALM/>}}
It is rare for case to serve only the distinguishing function, which overlaps greatly with the ‘identify’ function. Other ways of disambiguating the arguments of a transitive predicate (subject agreement, word order restriction, context, intonation, etc.) may explain this cross-linguistic observation. De Hoop and Malchukov argue that case systems that are completely based on the identification function must be richer in case morphology compared to languages based mainly on the distinguishing function.