论段玉裁的“上入声多转而为去声，平声多转为仄声” : 兼论声调源于韵尾假说

除了“古无去声之说”外，段玉裁还有一项关于上古汉语声调的重要论述，即“上人声多转而为去声，平声多转为仄声”。本文通过分析《六书音均表•诗经韵分十七部表》中韵字的上、中古调类差异指出，段氏实际认为上古平、上、人三声均可转人中古平、上、去、人四声，而上、人转为去，平转为仄则是对上、中古声调总体演变趋势的概括。此外，本文比较了段玉裁与唐作藩先生上古调类归属的异同，探究了段氏判断某字与中古异调的根据。本文还指出，汉语声调源于韵尾的假说，在解释段氏概括出的上、中古不同调类的转化现象时遇到了逻辑困难，该假说有待继续完善。
Besides the view that there was no Departing tone in Old Chinese, Duan Yucai also proposed that there were some characters of Rising and Entering tones in Old Chinese becoming Departingtone in Middle Chinese and some characters of Level tone becoming Oblique tones. Through the analysis of the book studying Old Chinese phonology by Duan Yucai, we point out that Duan Yucai actually believed that each of four tones in Middle Chinese originates from the three Old Chinese tones. After the comparison of the tone classification between Duan’s work and Professor Tang Zuofan, the reasons and methods for why and how Duan Yucai classified the characters into tone categories different from Middle Chinese are also discussed. Furthermore, we find that the hypothesis of Chinese tones arising from postcodas is in logic dilemma when explaining the tone changing phenomena summarized by Duan Yucai