Chóngniǔ (simplified Chinese: 重纽; traditional Chinese: 重紐; literally: "repeated button") or rime doublets are certain pairs of Middle Chinese syllables that are consistently distinguished in rime dictionaries and rime tables, but without a clear indication of the phonological basis of the distinction.
Rime dictionaries such as the Qieyun and Guangyun divided words by tone and then into rhyme groups. Each rhyme group was subdivided into homophone groups preceded by a small circle called a 紐 niǔ ("button"). The pronunciation of each homophone group was indicated by a fǎnqiè formula, a pair of characters having respectively the same initial and final sound as the word being described. Systematic analyses of the fanqie yield an enumeration of the initials and finals, but not their phonetic values. Rime tables such as the Yunjing further analysed the syllables distinguished by the rime dictionaries into initial consonant, "open" (kāi 開) or "closed" (hé 合), divisions (I–IV), broad rhyme class and tone. The closed distinction is generally considered to represent lip rounding, but the interpretation of the divisions is more controversial.
In most cases the different homophone groups within a Qieyun rhyme group are clearly distinguished in the rime tables by having a different initial or through the open/closed distinction. However some rhyme groups contain pairs of syllables that are distinguished only by being divided between divisions III and IV. These chongniu pairs occurred only with labial, velar or laryngeal initials. The Middle Chinese notations of Li Fang-Kuei and William Baxter distinguish the division IV parts using spellings containing both "j" and "i", without any commitment to pronunciation:
|Rhyme group||Li's notation||Baxter's notation|
|Division III||Division IV||Division III||Division IV|
This distinction is generally not reflected in modern varieties of Chinese but is maintained in some Sino-Vietnamese and Sino-Korean loans. For example, each of the following pairs is separated only in one of the Sinoxenic readings, in which the division IV element of the pair is distinguished by palatalization:
In the first pair, it is assumed that Vietnamese labials became dentals in a palatal environment. The nature of the distinction within Middle Chinese is disputed, with some scholars ascribing it to a medial and others to the main vowel.
According to the now prominent theory of Sergei Yakhontov, the chongniu division-III syllables (together with all syllables in division II) had a medial -r- in Old Chinese. William Baxter, following earlier ideas of Edwin Pulleyblank, holds that division-III chongniu syllables had medials -rj- in Old Chinese, while their counterparts in division IV had a medial -j- before a front vowel.
- Baxter, William H. (1992), A Handbook of Old Chinese Phonology, Berlin: Mouton de Gruyter, ISBN 978-3-11-012324-1.
- Branner, David Prager (2006), "What are rime tables and what do they mean?", in Branner, David Prager, The Chinese Rime Tables: Linguistic Philosophy and Historical-Comparative Phonology, Studies in the Theory and History of Linguistic Science, Series IV: Current Issues in Linguistic Theory 271, Amsterdam: John Benjamins, pp. 1–34, ISBN 978-90-272-4785-8.
- Norman, Jerry (1988), Chinese, Cambridge: Cambridge University Press, ISBN 978-0-521-29653-3.
- Pulleyblank, Edwin G. (1984), Middle Chinese: a study in historical phonology, Vancouver: University of British Columbia Press, ISBN 978-0-7748-0192-8.