Duan Yucai 段玉裁 (1735-1815), courtesy name Ruoying 若膺, style Maotang 懋堂, was a mid-Qing period 清 (1644-1911) scholar. He hailed from Jintan 金壇, Jiangsu, and was a disciple of the philosopher Dai Zhen 戴震 (1723-1777), whose adherent he would stay until the end of his life.
Duan occupied the office of magistrate (zhixian 知縣) of Yuping 玉屏, Guizhou, and Wushan 巫山, Sichuan, yet he returned to Suzhou 蘇州, Jiangsu, to care for his father.
As a disciple of Dai Zhen, Duan Yucai was also very interested in palaeography and the pronunciation of ancient Chinese. On the base of earlier research by Gu Yanwu 顧炎武 (1613-1682) and Jiang Yong 江永 (1681-1762) he developed a phonetic system that divided the sounds of Chinese into 6 groups and 17 sub-groups, as described in his book Liushu yinyun biao 六書音韻表.
Duan Yucai's most important book is a critical commentary to the Later Han period 後漢 (25-220 CE) character dictionary Shuowen jiezi 說文解字, the Shuowen jiezi zhu 說文解字注 (in the beginning also called Shuowen jiezi du 說文解字讀). This book is the first deep-going analysis of the shortcomings of Xu Shen's 許慎 (c. 58- c. 147) Shuowen that adds further results of research to the ancient analysis of Chinese characters. With the help of Han period literature, Duan Yucai was able to demonstrate that a lot of Xu Shen's statements were wrong or could at least be explained more in detail. Until today the Shuowen jiezi zhu is the most important and most detailed traditional commentary to the Shuowen.
Duan Yucai was of the opinion that the phonetic part of Chinese characters played a very crucial role in determining the meaning of the character and its shape, so that shape, sound and meaning of all characters supported each other to a refined system.
He also wrote the commentaries Shangshu guwen zhuanyi 尚書古文撰異, Maoshi guxun zhuan 毛詩故訓傳, Maoshi xiaoxue 毛詩小學, Zhouli Handu kao 周禮漢讀考, Yili Handu kao 儀禮漢讀考 and Zuoshi-Chunqiu gujing 左氏春秋古經.