Qieyun in the context of "Eastern Han Chinese"

Scholars have attempted to reconstruct the phonology of Old Chinese from documentary evidence. Although the writing system does not describe sounds directly, shared phonetic components of the most ancient Chinese characters are believed to link words that were pronounced similarly at that time. The oldest surviving Chinese verse, in the Classic of Poetry (Shijing), shows which words rhymed in that period. Scholars have compared these bodies of contemporary evidence with the much later Middle Chinese reading pronunciations listed in the Qieyun rhyme dictionary published in 601 AD, though this falls short of a phonemic analysis. Supplementary evidence has been drawn from cognates in other Sino-Tibetan languages and in Min Chinese, which split off before the Middle Chinese period, Chinese transcriptions of foreign names, and early borrowings from and by neighbouring languages such as Hmong–Mien, Kra-Dai, Vietic and Tocharian languages.

Although many details are disputed, most recent reconstructions agree on the basic structure. It is generally agreed that Old Chinese differed from Middle Chinese in lacking retroflex and palatal obstruents but having initial consonant clusters of some sort, and in having voiceless sonorants. Most recent reconstructions also posit consonant clusters at the end of the syllable, developing into tone distinctions in Middle Chinese.

Middle Chinese (formerly known as Ancient Chinese) or the Qieyun system (QYS) is the historical variety of Chinese recorded in the Qieyun, a rime dictionary first published in 601 and followed by several revised and expanded editions. The Swedish linguist Bernhard Karlgren believed that the dictionary recorded a speech standard of the capital Chang'an of the Sui and Tang dynasties. However, based on the preface of the Qieyun, most scholars now believe that it records a compromise between northern and southern reading and poetic traditions from the late Northern and Southern dynasties period. This composite system contains important information for the reconstruction of the preceding system of Old Chinese phonology (early 1st millennium BC).

The fanqie method used to indicate pronunciation in these dictionaries, though an improvement on earlier methods, proved awkward in practice. The mid-12th-century Yunjing and other rime tables incorporate a more sophisticated and convenient analysis of the Qieyun phonology. The rime tables attest to a number of sound changes that had occurred over the centuries following the publication of the Qieyun. Linguists sometimes refer to the system of the Qieyun as Early Middle Chinese and the variant revealed by the rime tables as Late Middle Chinese.

A rime dictionary, rhyme dictionary, or rime book (traditional Chinese: 韻書; simplified Chinese: 韵书; pinyin: yùnshū) is a genre of dictionary that records pronunciations for Chinese characters by tone and rhyme, instead of by graphical means like their radicals. The most important rime dictionary tradition began with the Qieyun (601), which codified correct pronunciations for reading the classics and writing poetry by combining the reading traditions of north and south China. This work became very popular during the Tang dynasty, and went through a series of revisions and expansions, of which the most famous is the Guangyun (1007–1008).

These dictionaries specify the pronunciations of characters using the fanqie method, giving a pair of characters indicating the onset and remainder of the syllable respectively.The later rime tables gave a significantly more precise and systematic account of the sounds of these dictionaries by tabulating syllables by their onsets, rhyme groups, tones and other properties. The phonological system inferred from these books, often interpreted using the rime tables, is known as Middle Chinese, and has been the key datum for efforts to recover the sounds of early forms of Chinese. It incorporates most of the distinctions found in modern varieties of Chinese, as well as some that are no longer distinguished. It has also been used together with other evidence in the reconstructions of Old Chinese.

A rime table or rhyme table (simplified Chinese: 韵图; traditional Chinese: 韻圖; pinyin: yùntú; Wade–Giles: yün-t'u) is a Chinese phonological model, tabulating the syllables of the series of rime dictionaries beginning with the Qieyun (601) by their onsets, rhyme groups, tones and other properties. The method gave a significantly more precise and systematic account of the sounds of those dictionaries than the previously used fǎnqiè analysis, but many of its details remain obscure. The phonological system that is implicit in the rime dictionaries and analysed in the rime tables is known as Middle Chinese, and is the traditional starting point for efforts to recover the sounds of early forms of Chinese. Some authors distinguish the two layers as Early and Late Middle Chinese respectively.

The earliest rime tables are associated with Chinese Buddhist monks, who are believed to have been inspired by the Sanskrit syllable charts in the Siddham script they used to study the language. The oldest extant rime tables are the 12th-century Yunjing ('mirror of rhymes') and Qiyin lüe ('summary of the seven sounds'), which are very similar, and believed to derive from a common prototype. Earlier fragmentary documents describing the analysis have been found at Dunhuang, suggesting that the tradition may date back to the late Tang dynasty.