The Chukotkan branch of the Chukotko-Kamchatkan family displays an unusual kind of ergativity, with unambiguously ergative case marking on nouns but an "ergative split" in the verb.
Based on Fortescue's (1997, 2003) reconstructions and the accusative patterning of Kamchatkan, ergative case marking appears to be an innovation in Chukotkan.
In several systems, there is syncretism between ergative and oblique marking in much of the pronominal and nominal inflectional paradigms (1pl, 2pl, 3sg, 3pl).
Existing research has amply noted language-specific variability in overt marking of ergative case on the subject, overt marking of accusative case on the object (differential object marking (DOM)), and concomitant effects on verbal agreement.
One diachronic implication of the observed synchronic patterns is that the Middle Indo-Aryan (MIA) ancestor system must have transitioned to across-the-board contrastive postpositional marking for ergative and accusative (DOM) cases via a stage in which such a contrast failed to exist for the majority of the nominal paradigm.
The hypothesis is that the oblique form was recruited for marking agents in perfective, transitive clauses as well as patients with high animacy/referentiality properties for those cells in the paradigm that lacked distinct inflectional ergative and accusative marking.
Its case marking follows the ergative absolutive pattern where the subject of an intransitive verb is in the absolutive case (which is unmarked), the same case being used for the direct object of a transitive verb.
The subject of a transitive verb is marked with the ergative case.
Accordingly, in her account, case is marked on an ergative-absolutive basis instead of a nominative-accusative basis in Tagalog; constructions like 29a above are treated as antipassives and those like 29b-d above as transitives.
Specific particles are used to indicate the relationship of nominals (e.g., nouns and noun phrases) to verbs, such as transitive verb object, agent passive verb; in some of the languages this system forms a sentence construction called ergative, in which all nominals are marked for their function and the verb stays unchanged.
