It is well known that during the course of their histories a number of Indo-European languages, all of them members of the Indo-Iranian branch of the family, developed an ergative construction. Thus, in certain tenses of the verb, their grammars came to treat in forlly identical manner the subject of an intransitive verb and the logical object of a transitive verb, the agent (or logical subject) of this latter being given a different morphological marker. Now although ergativity has been studied in a wide variety of languages as a synchronic phenomenon, the opportunities for examining it from a diachronic point of view are in the great majority of cases severely limited by lack of historical documentation. The Indo-Iranian languages, however, form a notable exception. These, thanks to the availability of texts from closely related languages covering a time-span of some three millennia, provide us with a chance to observe both the development of the construction and its subsequent decline. The present paper will do no more than attempt to trace a part of this process, namely the way in which the ergative construction has disappeared from a certain area of western Iranian. It bases its arguments upon the assumption that the geographical continuum of the Kurdish dialects, whose grammars exhibit the whole range of possibilities from fully ergative systems in the north to fully accusative systems in the south, reflects the successive stages of a diachronic process. This being granted, it should be possible by ordering the synchronic patterns of representative dialects from the northern, the central and the southern regions, to arrive at a picture of the historical sequence of events which has led to the loss of ergativity in the southern dialects and to isolate the mechanisms involved in their resultant restructuring. The wider problems of precisely how the construction arose historically and of why within the Indo-European family it appears to be confined to Indo-Iranian will not be dealt with here.