Final voiceless stops and therefore the checked "tones" have disappeared from most Mandarin dialects, spoken in northern and southwestern China, but have been preserved in southeastern Chinese branches like Yue, Min, and Hakka.
In languages such as Cantonese or Hakka, a small number of tonal distinctions exist (typically 2), which historically developed as a substitute for the lost Middle Chinese initial voicing.
Such clusters were later reduced to /s/, which, in turn, became /h/ and ultimately "departing tone" in Middle Chinese.
There were several unsuccessful attempts to classify the tones of Chinese before the establishment of the traditional four-tone description between 483 and 493.
The distinctive sound of syllables ending with a stop did not fit the three intonations and was categorised as the "entering tone" (入聲), thus forming the four-tone system.
[3] The use of this system flourished in the Sui and Tang dynasties (7th–10th centuries), during which the Qieyun (Chinese: 切韻) rime dictionary was written.
The Zhongyuan Yinyun (中原音韻), a rime book of 1324, already shows signs of glottal stop disappearing and the modern Mandarin tone system emerging in its place.
The Beijing dialect that forms the basis of Standard Mandarin redistributed syllables beginning with originally unvoiced consonants across the four tones in a completely random pattern.
There are several conditions that can be used to determine if a character historically had a checked tone in Middle Chinese based on its current reading in Modern Standard Mandarin.
However, there are many characters, such as 切, 塔, 六, 刻 and 骨 which do not satisfy any of these conditions at all.
Standard Cantonese does not use any glottal stops as final consonants; an exception is the sentence suffix 嘞 (laak).
As a result, Cantonese now has three entering tones:[12] Some variants of Yue Chinese, notably including that of Bobai County (Chinese: 博白; pinyin: Bóbái) in Guangxi and Yangjiang (simplified Chinese: 阳江; traditional Chinese: 陽江; pinyin: Yángjiāng; Cantonese Yale: Yèuhnggōng) in Guangdong,[13] have four entering tones: the lower light tone is also differentiated according to vowel length, short vowels for upper light and long vowels for lower light.
Thus in such varieties: Hakka preserves all Middle Chinese entering tones and is split into two registers.
Meixian Hakka dialect often taken as the paradigm gives the following: Middle Chinese entering tone syllables ending in [k] whose vowel clusters have become front high vowels like [i] and [ɛ] shifts to syllables with [t] finals in some of the modern Hakka,[15] as seen in the following table.
[17]: 39-40 The dark entering 陰入 tone on the other hand retains its glottal stop in sandhi environments.