But as a whole they [Kassites] were not Aryans. Though they adopted the Babylonian language and culture, the local scribes have recorded the Kassite … - Vere Gordon Childe

Aryan people first emerge from the gloom of prehistory on the northern borders of the Fertile Crescent of the Ancient East... So it is clear enough that the dynasts installed on the Upper Euphra­ tes by 1400 B.C. were Aryans, closely akin to those we meet in the Indus Valley and later in Media and Persia... (the first Aryans were racially Nordics and) the Nordic's superiority in physique fitted them to be vehicles of a superior language. (Childe 1926: 16,19,212)

[l]anguage, albeit an abstraction, is yet a more subtle and pervasive criterion of individuality than the culture-group formed by comparing flints and potsherds or the “races” of the skull-measurer. . . . they [the Aryans] must have possessed a certain spiritual unity reflected in and conditioned by their community of speech. To their linguistic heirs they bequeathed, if not skull types and bodily characteristics, at least something of this more subtle and precious, spiritual identity. . . . The Indo-European languages and their presumed parent-speech have been throughout exceptionally delicate and flexible instruments of thought. They were almost unique, for instance, in possessing a substantive verb and at least a rudimentary machinery for building subordinate clauses that might express conceptual relations in a chain of ratiocination. It follows then that the Aryans must have been gifted with exceptional mental endowments, if not in enjoyment of a high material culture. (p. 4)

These [Mitanni] numerals and divine and personal names are the oldest actual specimens of any Aryan speech which we possess. The forms deserve special attention. They are already quite distinctly Satem forms ; in fact, they are very nearly pure Indic. Certainly they are much more nearly akin to Sanskrit than to any of the Iranian dialects that later constituted the western wing of the Indo-Iranian family. Thus among the deities Nasatya is the Sanskrit form as opposed to the Zend Naonhaitya and all the four gods are prominent in the oldest Veda, while in the Iranian Avesta they have been degraded to secondary rank (Mithra), converted into demons (Indra) or renamed (Varuna =Ahura Mazda). The numerals are distinctively Indic not Iranian ; aika is identical with the Sanskrit eka while ' one ’ in Zend is aeva. So the s is preserved in Satta where it becomes h in Iranian (hapta) and the exact form is found, not indeed in Sanskrit, but in the Prakrits which were supposed to be post-Vedic. Even the personal names look Indic rather than Iranian. Thus Biridaswa has been plausibly compared with the Sanskrit Brhadasva (owning a great horse). If this be right the second element, asva, horse, is in contrast to the Iranian form aspa seen in Old Persian and Zend. ... Finally we know that there existed among the Mitanni at this time a class of warriors styled maryanni which has suggested comparison with the Sanskrit marya young men, heroes.