Historical linguistic sources of Kurdish date back just a few hundred years, thus it is not possible to track the profound grammatical changes of Western Iranian languages in Kurdish. Through a comparison with attested languages of the Middle Iranian period, this paper provides a hypothetical chronology of grammatical changes. It allows us to tentatively localise the approximate time when modern varieties separated with regard to the respective grammatical change. In order to represent the types of linguistic relationship involved, distinct models of language contact and language continua are set up.