Chinese is documented over a long period of time, with the earliest oracle bone writings dated to c. 1250 BC.
There was a well-developed system of derivational and possibly inflectional morphology, formed using consonants added onto the beginning or end of a syllable.
Although there is no standard system for subdividing these periods, the following is an approximate chronology leading from the oldest writings in the oracle bone script up through modern Standard Mandarin: A native tradition of Chinese phonology developed in the Middle Chinese period.
During the early centuries AD, however, the more advanced method of fanqie was developed, which allowed the pronunciation of any syllable to be specified unambiguously by using one character to indicate the initial consonant and another to indicate the remainder.
During the next few centuries, the increasing influence of Buddhism and Buddhist scholars brought Chinese linguists in touch with the tradition of Sanskrit grammar, which included a highly advanced understanding of phonology and phonetics, including a system of analyzing sounds by distinctive features, such as place of articulation and type of phonation.
This led to rime tables such as the Yunjing (c. 1150 AD), a sophisticated analysis of the sound system of the Qieyun.
During the Qing dynasty (1644–1912), scholars such as Duan Yucai diligently studied the sound system of Middle and Old Chinese.
Through careful examination of rime tables, rime dictionaries and patterns of rhyming among poets of various eras, these scholars were able to work out the system of categories of rhymes in Old Chinese, and discover additional Middle Chinese categories that had previously been overlooked.
However, progress in Chinese linguistics was seriously hampered by the lack of any concept of a phoneme — i.e. a basic unit of sound, including vowels and vowel-like segments as well as consonants.
This made it impossible to go beyond determination of systems of rhyming categories to reconstruction of the actual sounds involved.
In some ways, the lack of native Chinese development of the concept of a unit of sound is surprising, as it had already been developed by Sanskrit grammarians such as Pāṇini by the 4th century BC at the latest, and the phonological analysis of the Yunjing shows a close familiarity with the tradition of Sanskrit grammar.
It seems likely, however, that As a result, the first reconstructions of the actual sound systems of Old and Middle Chinese were only done in the early 20th century, by Swedish sinologist Bernhard Karlgren.
Armed with his knowledge of Western historical linguistics, he performed field work in China between 1910 and 1912, creating a list of 3,100 Chinese characters and collecting phonological data on the pronunciation of these characters in 19 Mandarin dialects as well as the dialects of Shanghai (Wu), Fuzhou (Eastern Min), and Guangdong (Cantonese).
He combined this with the Sino-Japanese and Sino-Vietnamese pronunciations as well as previously published material on nine other dialects, along with the fanqie analysis of the Guangyun rime dictionary (a later version of the Qieyun of 601 AD).
Walter Simon and Henri Maspero also made great contributions in the field during the early days of its development.
The following is an approximate consensus, based on the system of William Baxter and (earlier) Li Fang-Kuei: William H. Baxter pointed out that some of the words that were reconstructed with Middle Chinese palatal initials were perhaps words that had velar initials in Old Chinese.
[3] This is supported by Baxter's observation that modern Min dialects show a difference in pronunciation between 厚 and 後, both of which belong to the Middle Chinese 匣 initial (reconstructed as *ɣ~ɦ).
The second character is pronounced by these dialects with a null initial, possibly reflecting a voiced laryngeal in Old Chinese.
[4] The OC *ɡ remained intact in Type B syllables, which correspond to Division III Middle Chinese words.
[6] Both Baxter and Sagart have pointed out that Old Chinese had a series of voiceless sonorants, which typically do not occur in most modern varieties.
Their reflexes in Middle Chinese are postulated to be: Additionally, the OC lateral consonant /*l/ is shown to have fortified to a coronal plosive /d/ in Type A syllables.
Furthermore, Baxter considers all the distinctions of the Qieyun to be real, while many of them are clearly anachronisms that no longer applied to any living form of the language in 600 AD.
The exact changes involving finals are somewhat complex and not always predictable, in that in many circumstances there are multiple possible outcomes.
In fact, some post-LMC changes are reflected in all modern varieties, such as the loss of the chongniu distinction (between e.g. /pian/ and /pjian/, using Edwin Pulleyblank's transcription).