The Indo-Iranian labial-extended causative suffix

Alongside the expected reflexes of the Proto-Indo-European causative suffix *-éie̯/o-, there appears in Indo-Iranian a second, expanded version that contains a labial consonant: Indic -(ā)páya- and Eastern Iranian (EIr.) *-(ā)u̯aia̯-, the latter continued in Khotanese -ev-, Khwarazmian -(’)wy-, and other modern EIr. languages. In this paper, we will argue that *-(ā)u̯aia̯- is also the source of a causative marker in two closely related Caspian (Western Iranian) languages, Gilaki and Tati-Talyshi, through a reconstructable Proto-Caspian form *-āwēn-. We propose that these three suffixes, -(ā)páya-, *-(ā)u̯aia̯-, and *-āwēn-, originated in Proto-Indo-Iranian, through the rounding of a root-final laryngeal to a labial sound in causative formations.