本文利用音韻規律、諧聲串聯和方言比較論證中古日母字源自上古舌根濁塞音合口 三等。這個分析不但擺脫文獻兩種構擬 *Ñ 和 *Ñ 的弊端，成功地詮釋了日母的語音演 變，也顧及其它聲母的特殊方音。至於日母的源頭到底是 *gʰ 抑或兼有 *g、*gʰ，暫無 定論。本文分析的理論貢獻有：（一）諧聲問題訴諸音變即可，不需擬設複聲母， （二）次濁聲母讀h、x、ɦ、ɣ 是語音演變的必然，無關氣流換道。有別於韻書聚焦個別 漢字，本文主張關注以聲符為軸發展出來的群組，並檢視方言音讀，能更全面的掌握漢 語音韻的演變脈絡。

This paper argues that the Middle-Chinese Ri-initial descends from voiced velar stop(s) plus Closed-Mouth Division III in Old Chinese, by means of phonological rules (labiolization of velars), Xiesheng and dialect comparison. This analysis not only gets rid of drawbacks of the two reconstructions *Ñ and *Ñ in the literature, but also sucessfully explains irregular pronunciations of some Middle-Chinese initials in various dialects. Yet, whether the Ri-initial originates from *gʰ or *g, *gʰ both awaits further investigation. Two theoretical implications of the current analysis are: (a) consonant-cluster porposals are unnecessary to solve the Xiesheng problem, and (b) pronunciations of h, x, ɦ, ɣ by Cizhuo initials derive directly from sound changes. Different from Qieyun which focuses on individual characters and uses limited dialect materials, this paper advocates that a more adequate and convincing methodology to ensure diachronic developments of Chinese phonology appeals to Xiesheng and a wide range of synchronic phonologies.