The Qieyun is a rhyme book written by the scholar Lu Fayan 陆法言 in 601 CE, during the Sui dynasty. In my degree thesis I'm trying to analyse some aspects of this particular work.
Recently, I managed to translate the preface of the Qieyun by myself. Here you can find an online version of it. However, there are some obscure points. For the purpose of my thesis the most serious doubt I'm facing has to do with the following sentence:
Now, in the page I've just linked there is an explanation in modern Chinese of the contents of Lu Fayan's preface. If I scroll down I read that the previous sentence means:
The problem is: how should I interpret the phrase
共用一个上字来切的? The world 上字 has a specific meaning, it represents the first character used as an initial speller in a fanqie spelling. Nevertheless, as I've just said, 上字 refers to the initial consonant of a syllable or 声母, not to the rhyme or 韵母. It seems strange to me because in the previous sentences Lu Fayan was talking exactly about rhymes:
秦陇则去声为入，梁益则平声似去。又支（章移反）、脂（旨夷反）、鱼（语居反）、虞（语俱反）共为一韵，[...] (next comes the first sentece I gave you)
In Qin-Long region (North-West China) the departing tone (去声) becomes the entering tone (入声), while in Liang-Yi region (South-West) the level tone (平声) is pronounced in the same way as the departing tone. Moreover, the rhymes 支, 脂, 鱼 and 虞 are considered identical.
I asked my chinese friend who studied Linguistics and Historical Chinese Phonology. She looked the explanation proposed by Baidu Baike and concluded that 上字 here simply means "the character 上". According to her, the sentence means that the character 上 could be used to write the fanqie spelling of the characters 先, 仙, 尤 and 侯 in some southern dialect of the time. In other words, they all rhyme with 上 (MC dzyangH) which has the final -jangH in Baxter's notation of Middle Chinese. However, I think she deduced it only based upon the explanation of Baidu because in the original text the character 上 is not mentioned.
So, after all the above considerations, it seems to me that the foundamental question lies in the true interpretation of the phrase in the explanation. By only looking at Lu Fayan's original text I'm not able to give a meaningful translation of that sentence.
In your opinion, is my friend's view correct? If not, how should I interpret the sentence? What could an proper translantion be?