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The exact scope of the Eastern branch of the Indo-Aryan languages is controversial. All scholars agree about a kernel that includes the Odia cluster and the Bengali–Assamese languages, while many also include the Bihari languages. The widest scope was proposed by Suniti Kumar Chatterji who included the Eastern Hindi varieties, but this has not been widely accepted.
When the Bihari languages are included, the Eastern Indo-Aryan languages fall into four language groups in two broader categories:
Grammatical features of the Eastern Indo-Aryan languages:
Case
Bengali
Assamese
Odia
Rajbangshi
Surjapuri
Maithili
Bhojpuri
Tharu
Sylheti
Instrumental
-t̪e, -ke d̪ie
-e, -er-e, di, -e-di
-e, -re, -d̪ei
-d̪i
sɛ
-e,e˜, sə˜, d̪ea
le, leka
-re, di
Dative
-ke, -re
-k, -ɒk
-ku
-k, -ɔk
-k, -ɔk
-ke˜
-ke
-hənə
-gu, -gur
Ablative
-t̪ʰeke
-pɒra
-u, -ru, -ʈʰaru, -ʈʰiru
-hat̪ɛ, t̪ʰaki
-sɛ
-sə˜, -k -karəne
se
-lagi, -tône
Genitive
-r, -er
-r, -ɒr
-rɔ
-r, -ɛr
-r, -ɛr
-ker (-k)
-kæ
-ək
-r, -ôr
Locative
-e, -t̪e
-t, -ɒt
-re
-t̪, -ɔt̪
-t̪, -ɔt̪
e, me, -hi, -tə
-mə
-t, -ô
Eastern Indo-Aryan languages display many morphosyntactic features similar to those of Munda languages, while western Indo-Aryan languages do not. It is suggested that "pre-Munda" ("proto-" in regular terminology) languages may have once dominated the eastern Indo-Gangetic Plain, and were then absorbed by Indo-Aryan languages at an early date as Indo-Aryan spread east.
Cardona, George; Jain, Dhanesh, eds. (2003), "The historical context and development of Indo-Aryan", The Indo-Aryan Languages, Routledge language family series, London: Routledge, pp. 46–66, ISBN0-7007-1130-9
South Asian folklore: an encyclopedia : Afghanistan, Bangladesh, India, By Peter J. Claus, Sarah Diamond, Margaret Ann Mills, Routledge, 2003, p. 203
Masica, Colin (1991). The Indo-Aryan Languages. Cambridge: Cambridge University Press. pp. 446–462.