The phonological system of Old Korean cannot be established "with any certainty", and its study relies largely on tracing back elements of Middle Korean (MK) phonology.
Prosody Fifteenth-century Middle Korean was a
tonal or
pitch-accent language whose orthography distinguished between three tones: high, rising, and low. The rising tone is analyzed as a low tone followed by a high tone within a
bimoraic syllable. Middle Chinese was also a tonal language, with
four tones: level, rising, departing, and entering. The tones of fifteenth-century Sino-Korean partially correspond to Middle Chinese ones. Chinese syllables with level tone have low tone in Middle Korean; those with rising or departing tones, rising tone; and those with entering tone, high tone. These correspondences suggest that Old Korean had some form of
suprasegmentals consistent with those of Middle Chinese, perhaps a tonal system similar to that of Middle Korean. Phonetic glosses in Silla Buddhist texts show that as early as the eighth century, Sino-Korean involved three tonal categories and failed to distinguish rising and departing tones. On the other hand, linguists such as Ki-Moon Lee and S. Roberts Ramsey argue that Old Korean originally had a simpler prosody than Middle Korean, and that influence from Chinese tones was among the reasons for Korean tonogenesis. The hypothesis that Old Korean originally lacked phonemic tone is supported by the fact that most Middle Korean nouns conform to a tonal pattern, the tendency for ancient Korean scribes to transcribe Old Korean proper nouns with Chinese level-tone characters, and the accent marks on Korean proper nouns given by the Japanese history
Nihon Shoki, which suggest that ancient Koreans distinguished only the entering tone among the four Chinese tones.
Syllable structure Middle Korean had a complex
syllable structure that allowed clusters of up to three consonants in initial and two consonants in terminal position, as well as vowel triphthongs. But many syllables with complex structures arose from the merger of multiple syllables, as seen below. Middle Korean
closed syllables with bimoraic "rising tone" reflect an originally bisyllabic CVCV form in which the final vowel was reduced, and some linguists propose that Old Korean or its precursor originally had a CV syllable structure like that of Japanese, with all clusters and coda consonants forming due to vowel reduction later on. However, there is strong evidence for the existence of coda consonants in even the earliest attestations of Korean, especially in
mareum cheomgi orthography. On the other hand, Middle Korean consonant clusters are believed not to have existed in Old Korean and to have formed after the twelfth century with the loss of intervening vowels. Old Korean thus had a simpler syllable structure than Middle Korean.
Consonants The consonant inventory of fifteenth-century Middle Korean is given here to help readers understand the following sections on Old Korean consonants. These are not the consonants of
Old Korean, but of its fifteenth-century descendant. Three of the nineteen Middle Korean consonants could not occur in word-initial position: , , and . Only nine consonants were permitted in the syllable coda. Aspiration was lost in coda position; coda merged with ; and , , , and the reinforced consonants could not occur as the coda. Coda was preserved only word-internally and when followed by another voiced fricative; otherwise it merged with .
Nasals Sino-Korean evidence suggests that there were no major differences between Old Korean and Middle Korean nasals. Middle Chinese onset is reflected in Sino-Korean as a null initial, while both Chinese and Korean transcriptions of Old Korean terms systematically avoid characters with onset . Middle Korean
phonotactic restrictions on thus seem to have held true for Old Korean as well. The
Samguk Sagi sometimes alternates between nasal-initial and liquid-initial characters in transcribing the same syllable of the same proper noun. This suggests that Old Korean may have had a
sandhi rule in which nasals could become liquids, or vice versa, under certain circumstances.
Aspirate consonants The Middle Korean series of
aspirated stops and affricates developed from mergers of consonant clusters involving /h/ or a
velar obstruent, which in turn had formed from the loss of intervening vowels. To what extent this process had occurred in the Old Korean period is still debated. Middle Chinese had a phonemic distinction between aspirated and unaspirated stops. This is reflected somewhat irregularly in Sino-Korean. Based on this variable reflection of Middle Chinese aspirates, Korean is thought to have developed the dental aspirates and first, followed by and finally . is often believed to have been absent when Sino-Korean was established. Silla scribes used the aspirate-initial characters only infrequently. When they did, the aspirates were often replaced with unaspirated equivalents. For instance, the 757 standardization of place names sometimes involved changing aspirated phonograms for unaspirated ones, or vice versa. This suggests that aspiration of any sort may have been absent in Old Korean, or that aspirate stops may have existed in
free variation with unaspirated ones but were not distinct phonemes. On the other hand, Ki-Moon Lee and S. Roberts Ramsey argue that Silla orthography confirms the existence in Old Korean of at least the dental aspirates as phonemes. Meanwhile, Nam Pung-hyun believes that Old Korean had and but may have lacked and , while noting that the
functional load of the aspirates was "extremely low".
Origin of MK /h/ Some characters with initial in Middle Chinese are reflected in Sino-Korean as . Conversely, some instances of the Middle Chinese initial , usually loaned as Sino-Korean , are found as Sino-Korean . This may be because Koreans mistakenly assigned the same initial consonant to characters which do share a phonetic
radical but in practice had different Middle Chinese initials. On the other hand, this may reflect a
velar value for the Old Korean ancestor of Middle Korean . Korean scholars often propose an Old Korean
velar fricative as ancestral to Middle Korean . Some orthographic alternations suggest that Silla writers did not distinguish between Middle Chinese initial and initial , although linguist Marc Miyake is skeptical of the evidence, while some Middle Korean
allomorphs alternate between and a velar. Linguist Wei Guofeng suggests that the Old Korean phonemes and had overlapping distributions, with allophones such as being shared by both phonemes. Alexander Vovin also argues via
internal reconstruction that intervocalic in earlier Korean
lenited to Middle Korean .
Origin of MK lenited phonemes Sibilants In some pre-Unified Silla transcriptions of Korean proper nouns, Chinese
affricate and
fricative sibilants appear interchangeable. This has been interpreted as some stage of Old Korean having lacked the Middle Korean distinction between and . The
hyangga poems, however, differentiate affricates and fricatives consistently, while the Chinese distinction between the two is faithfully preserved in Sino-Korean phonology. Koreans thus clearly distinguished from by the eighth century, and Marc Miyake casts doubt on the notion that Korean ever had a stage where affricates and fricatives were not distinct.
Liquids Middle Korean had only one
liquid phoneme, which varied between and . Old Korean, however, had two separate liquid phonemes. In Old Korean orthography, this first liquid phoneme was represented by the PAP , whose Old Chinese value was *l̥[ə]j, and the second phoneme by the PAP , whose Old Chinese value was *qrət. Besides this orthographic variation, the distinction between the liquid phonemes is also suggested by the tonal behavior of Middle Korean verb stems ending in . According to Alexander Vovin, Ki-Moon Lee asserts that represented and that represented . Vovin considers this claim "unacceptable" and "counterintuitive", especially given the reconstructed Old Chinese pronunciations of both characters, and suggests instead that represented while stood for a
rhotic. Ramsey and Nam Pung-hyun both agree with Vovin's hypothesis.
Coda consonants Vowels == Grammar ==