The vernaculars spoken by the Kurds fall in two groups, each again being divided into two main dialect groups. The great majority of the Kurds speak a variety of the socalled Kurmanci or Sorani dialects; smaller numbers speak Gorani or Zaza. Although the latter two dialects are close relatives of the former two, they do not strictly speaking belong to the same branch of Indo-Iranian languages. Nonetheless, both groups are commonly thought to belong to the Northwestern group of Iranian languages.

[...]

I would like to use this theoretical framework to focus on specific kinds of questions relating to the language contact phenomena mentioned above. MacKenzie (1961b: 86) argued that the grammatical features distinguishing Sorani from Kurmanci are due to a Gorani substratum, i.e., to traces of the language spoken in the area before a presumed ’Kurdish invasion’. My main argument, presented in part 3 of this paper, will be that these closer affinities between Central Kurdish and Gorani are best seen not as a substratum (presumably preceding the Mongol invasions), but rather as prestige borrowings of a much later date, probably not before the seventeenth century. This process need not have involved any serious language shift among the Gorani population, as an account in terms of substratal influence would imply.

Kurdish