王驥德《曲律．論腔調》曰：「在南曲則但當以吳音為正」，吳音指崑山水磨調，所謂「南曲度曲論」指崑腔度曲論。本文從平仄四聲、四聲陰陽、用韻、閉口音，逐次分析王驥德建構南曲度曲論，包括：其一，依循吳語音系以區別於中州音系的北曲，如入聲獨立，四聲陰陽，區分開合洪細。其二，禁用土音，如不辨開口與閉口，不分開口與合口。其三，保留存在於中州音系而吳語卻已消失的閉口韻。其四，採中州陰平、陽平、上、去的聲調系統，但在「平仄」二分的曲律架構下，突出吳語聲母分清濁和保持入聲的特色。王驥德運用音韻學著力建構的是劇作家依律填詞的製曲論，同時將填詞製曲和歌唱度曲之關係做了緊密繫聯；其中「鄉音變體」是其製曲與度曲的語言元素，提供創作或歌唱南曲正聲的崑山腔之準繩，其南曲度曲論之傳承與建構及卓越成就在此。

In his “On the Accents and Tones of Qu” (Lun qiangdiao, collected in Qulü), Wang Jide (?-1623) claims that, “In the southern traditional Chinese opera, we should take the sounds of Wu as the standard.” What Wang called the sounds of Wu means Kunshan shuimo melody patterns. The theory of duqu (musical composition) of traditional southern Chinese opera signifies, in Wang’s opinion, the theory of musical composition of these Kun accents. The paper will analyze Wang Jide’s theory of duqu or musical composition of traditional southern Chinese opera, in terms of four aspects: level and oblique tone configurations (ping and ze) and the four tones; yin and yang characteristics of tones; the usage of rhyme types; and rhyme sounds ending with final -m (bikou). More specifically, the author mainly discusses Wang’s four arguments about the theory of musical composition in traditional southern Chinese opera. First, Wang studied the Wu phonetic system to differentiate it from the northern traditional Chinese opera with its system of Zhongzhou sounds. For instance, the entering (ru) tones should be independent from other tones; the four tones are separated into yin and yang; and it is necessary to distinguish the different mouth shapes (such as open or closed) right after pronouncing finals. Secondly, we explore Wang’s forbidding the use of local accents, which combined the sounds of the -m final and rhymes beginning or ending with rhymes i, u, and y (kaikou), or did not separate kaikou from rhymes beginning or ending with rhyme u (hekou). Thirdly, Wang had his own opinions on those –m final rhymes that still remained in the set of sounds of Zhongzhou, but had disappeared in the sounds of Wu. Fourthly, utilizing the sounds of level yin (yin ping), level yang (yang ping), rising (shang), and falling (qu) in the Zhongzhou system, Wang highlighted the distinguishing feature in the initials of sounds of Wu that the voiceless (qing) initials are distinguished from the voiced (zhuo) initials, and the feature of entering (ru) tones remaining in the Wu set. The two features are formed under the structure of the dichotomy between level and oblique tones (ping and ze). What Wang Jide was engaged in constructing was a quite phonological theory about how a playwright composes words according to rhymes. In addition, he tightly connected the relation between composing and singing to produce qu music. In the view of the theory, one of the significant language elements when composing and producing qu music is the way the local language works as a template to change the official language (xiangyin bianti—the change due to local accents, meaning that an official language is mixed with local accents). The bianti or altered language not only provides a linguistic criterion to create or sing the authentic accents of Kunshan, but also represents a well-structured and eminent achievement inherited from the theory of musical composition, or duqu, in traditional southern Chinese opera.