a process now known as tonogenesis. Haudricourt further proposed that tone in the other languages, including Middle Chinese, had a similar origin. Other Middle Chinese (formerly known as Ancient Chinese) or the Qieyun system (QYS) is the historical variety of Chinese recorded in the Qieyun, a rhyme dictionary first published in 601 and followed by several revised and expanded editions. The Swedish linguist Bernhard Karlgren thought that the dictionary recorded a speech standard of the capital Chang'an of the Sui and Tang dynasties. However, based Based on Annen's description, other similar statements and related data, Mei Tsu-lin concluded that the level tone was long, level and low, the rising tone was short, level and high, the departing tone was somewhat long and probably high and rising, and the entering tone was short (as the syllable ended in a voiceless stop) and probably high. The tone system of Middle Chinese is strikingly similar to those of its neighbours in the Mainland Southeast Asia linguistic area—proto-Hmong–Mien, proto-Tai and early Vietnamese—none of which is genetically related to Chinese. Moreover, the earliest strata of loans display a regular correspondence between tonal categories in the different languages. In 1954, André-Georges Haudricourt showed that Vietnamese counterparts of the rising and departing tones corresponded to final /ʔ/ and /s/, respectively, in other (atonal) Austroasiatic languages. He thus argued that the Austroasiatic proto-language had been atonal, and that the development of tones in Vietnamese had been conditioned by these consonants, which had subsequently disappeared, a process now known as tonogenesis. Haudricourt further proposed that tone in the other languages, including Middle Chinese, had a similar origin. Other scholars have since uncovered transcriptional and other evidence for these consonants in early forms of Chinese, and many linguists now believe that Old Chinese was atonal. Around the end of the first millennium AD, Middle Chinese and the southeast Asian languages experienced a phonemic split of their tone categories. Syllables with voiced initials tended to be pronounced with a lower pitch, and by the late Tang dynasty, each of the tones had split into two registers conditioned by the initials, known as the "upper" and "lower". When voicing was lost in most varieties (except in the Wu and Old Xiang groups and some Gan dialects), this distinction became phonemic, yielding up to eight tonal categories, with a six-way contrast in unchecked syllables and a two-way contrast in checked syllables. Cantonese maintains…

Tonogenesis is a topic of perennial interest in Trans-Himalayan linguistics (the name of the family is the subject of some debate. Other terms for the family are Sino-Tibetan and Tibeto-Burman). The phonetic origins of the tones of the many languages in the family, such as Tibetan (Huáng 1995), Burmese (Nishi 1999; Hill 2019), and Chinese (Haudricourt 1954; Sagart 1999) are relatively well understood. However, the phonetic origins of tone in many Trans-Himalayan languages remains an open question (Sagart 2006). There has been a paucity of work describing the origins of tone in the languages cl