Abstract
Abstract This paper offers new evidence from Stau, Geshiza, and Khroskyabs to address the question of directionality in valency-changing derivations in Sino-Tibetan. Examining Stau, Geshiza, and Khroskyabs causative and anticausative verb stem pairs adds to the evidence that in Proto-Sino-Tibetan, a number of intransitive stems are derived from transitive stems, in some cases as the result of *N‑ prefixation, and in other cases from voicing alternation independent of *N‑ prefixation. In addition, the proto-sigmatic prefix (*s-) does not cause devoicing in Stau, Geshiza, and Khroskyabs, but rather often undergoes voicing assimilation, and has more than just a causativization function. Furthermore, by looking at Gyalrong, Minyag, Tangut, Middle Chinese, and Old Chinese we emphasize that there is no synchronic evidence to support devoicing induced by *s‑, nor is there historical evidence to support the claim that *s‑ caused devoicing in Proto-Gyalrongic, or even at genetically deeper stages.