Indo-Aryan languages have the longest documented historical record, with the earliest attested texts going back to 1900 bce. Old Indo-Aryan (Vedic, Sanskrit) had an inflectional case-marking system where nominatives functioned as subjects. Objects could be realized via several different case markers (depending on semantic and structural factors), but not the nominative. This inflectional system was lost over the course of several centuries during Middle Indo-Aryan, resulting in just a nominative–oblique inflectional distinction. The New Indo-Aryan languages innovated case markers and developed new case-marking systems. Like in Old Indo-Aryan, case is systematically used to express semantic differences via differential object marking constructions. However, unlike in Old Indo-Aryan, many of the New Indo-Aryan languages are ergative and all allow for non-nominative subjects, most prominently for experiencer subjects. Objects, on the other hand, can now also be unmarked (nominative), usually participating in differential object marking. The case-marking patterns within New Indo-Aryan and across time have given rise to a number of debates and analyses. The most prominent of these include issues of case alignment and language change, the distribution of ergative vs. accusative vs. nominative case, and discussions of markedness and differential case marking.
Case and agreement patterns that are present in Old, Middle, and New Indo-Aryan languages have been argued to require the following perspective: since ergative case marking and ergative (object) agreement in these languages are historically tied to having originated from the past perfective morphological marker ta, they can only be fully understood from a perspective that factors in this development. Particular attention is given to the waxing and waning of ergative properties in Late Middle Indo-Aryan and New Indo-Aryan, which give rise to recurring dissociation of case and agreement; specifically, object agreement in the absence of ergative case marking is attested in Kutchi Gujarati and Marwari, whereas ergative case marking without object agreement is present in Nepali. With regard to case, recent insights show that “ergative/accusative” may be regularly semantically/pragmatically conditioned in Indo-Aryan (so-called differential case marking). Pertaining to agreement, a central theoretical question is whether “ergative” object agreement should be analyzed uniformly with subject agreement or, alternatively, as a type of participle agreement—drawing on synchronic parallels between Indo-Aryan and Romance.