Karlgren–Li reconstruction of Middle Chinese

The Karlgren–Li reconstruction of Middle Chinese was a representation of the sounds of Middle Chinese devised by Bernhard Karlgren and revised by Li Fang-Kuei in 1971, remedying a number of minor defects.

The Qieyun rime dictionary was created by Lu Fayan in 601 as a guide to proper pronunciation, particularly for the reading of classic texts. The dictionary divided characters between the four tones, which were subdivided into 193 rhyme groups and then into homophone groups. The pronunciation of each homophone group is given by a fanqie formula, a pair of common characters respectively indicating the initial and final sounds of the syllable. Lu Fayan's work was very influential, and led to a series of expanded and corrected versions following the same structure, the most important of which is the Guangyun (1007–08). The Qieyun was thought lost until the mid-20th century, and scholars worked from the Guangyun. Fortunately it was later found that the Guangyun had preserved the phonological system of the Qieyun with no significant change. The Qing dynasty scholar Chen Li analysed the fanqie spellings of the Guangyun, determining which initial and final spellers represented the same sounds, and thus enumerating the initials and finals of the underlying system. However this method gave no indication of how these were pronounced.

A series of rime tables from the Song dynasty incorporated a more sophisticated analysis, though the language had changed since the time of the Qieyun. The initials were identified and categorized by place and manner of articulation. Finals were classified into 16 rhyme classes (攝 shè). Within each rhyme class, syllables were classified as either "open" (開 kāi) or "closed" (合 hé), as belonging to one of the four tones, and as belonging to one of four divisions (等 děng), indicated by rows of the table. The Qing philologists found that some of the finals of the rime dictionaries were always placed in the first row, some always in the second and some always in the fourth, and they were thus named finals of divisions I, II and IV respectively. The remaining finals were spread across the second, third and fourth rows, and were later called division III finals.

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