A checked tone, commonly known by the Chinese calque entering tone, is one of the four syllable types in the phonology of Middle Chinese. Although usually translated as "tone", a checked tone is not a tone in the phonetic sense but rather a syllable that ends in a stop consonant or a glottal stop. Separating the checked tone allows -p, -t, and -k to be treated as allophones of -m, -n, and -ng, respectively, since they are in complementary distribution. Stops appear only in the checked tone, and nasals appear only in the other tones. Because of the origin of tone in Chinese, the number of tones found in such syllables is smaller than the number of tones in other syllables. Chinese phonetics have traditionally counted them separately.
For instance, Cantonese has six tones in syllables that do not end in stops but only three in syllables that do. That is why although Cantonese has only six tones, in the sense of six contrasting variations in pitch, it is often said to have nine tones.
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.
Tones are an indispensable part of Chinese literature, as characters in poetry and prose were chosen according to tones and rhymes for their euphony. This use of language helps reconstructing Old Chinese and Middle Chinese pronunciations since Chinese writing system is logographic, rather than phonetic.
Phonetics
From a phonetic perspective, the entering tone is simply a syllable ending with a voiceless stop that has no audible release: or . In some Chinese variants, the final stop has become glottal stop .
History
The voiceless stops that typify the entering tone date back to the Proto-Sino-Tibetan, the parent language of Chinese as well as the Tibeto-Burman languages. In addition, Old Chinese is commonly thought to have syllables ending in clusters , , and (sometimes called the "long entering tone" while syllables ending in , and are the "short entering tone"). Such clusters were later reduced to /s/, which, in turn, became and ultimately "departing tone" in Middle Chinese.
The first Chinese philologists began to describe the phonology of Chinese during the Early Middle Chinese period (specifically, during the Northern and Southern Dynasties, between 400 and 600 AD), under the influence of Buddhism and the Sanskrit language that arrived along with it. There were several unsuccessful attempts to classify the tones of Chinese before the establishment of the traditional four-tone description between 483 and 493. It is based on the Vedic theory of three intonations (). The middle intonation, , maps to the "level tone" (); the upwards intonation, , to the "rising tone" (); the downward intonation, , to the "departing tone" (). The distinctive sound of syllables ending with a stop did not fit the three intonations and was categorised as the "entering tone" (), thus forming the four-tone system. The use of this system flourished in the Sui and Tang dynasties (7th–10th centuries), during which the Qieyun () rime dictionary was written.
Note that modern linguistic descriptions of Middle Chinese often refer to the level, rising and departing tones as tones 1, 2 and 3, respectively.
By the time of the Mongol invasion (the Yuan dynasty, 1279–1368), the former final stops had been reduced to a glottal stop in Old Mandarin. The Zhongyuan Yinyun (), a rime book of 1324, already shows signs of glottal stop disappearing and the modern Mandarin tone system emerging in its place. The precise time at which the loss occurred is unknown though it was likely gone by the time of the Qing Dynasty, in the 17th century.
Example
Entering tone in Chinese
Mandarin
The entering tone is extant in Jianghuai Mandarin and Minjiang Sichuanese. Other dialects have lost the entering tone, and syllables that had the tone have been distributed into the four modern tonal categories, depending on their initial consonants.
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. For example, the three characters , all pronounced in Middle Chinese (William Baxter's reconstruction), are now pronounced , with tones 1, 3 and 4 respectively. The two characters , both pronounced , are now pronounced and respectively, with the character splitting on semantic grounds (tone 3 when it is used as a component of a name, mostly tone 2 otherwise).