15세기 이중모음 체계와 순경음의 변화

During the 15th century, "wa, wə, wi" were not considered rounded diphthongs at the phonological level of the Korean vowel system. However, "wa, wə, wi" existed only through allophone level. Although they existed, they could not be written in letters. During the 15th century, "ㅘ, ㅝ" represented the chain of two vowels, that is "ㅘ → ㅗ + ㅏ(oa)" and "ㅝ → ㅜ + ㅓ(uə)." Some sound changes, such as "ㅸ>w(β>w)", made "wa, wə, wi" on the phonetic level. Scholars active during this period attempted to distinguish the original "ㅘ, ㅝ" between the phonetic "ㅘ, ㅝ." Because "wa, wə, wi" did not include unique characters, they were forced to use "ㅘ(oa), ㅝ(uə)". As a result, "ㅘ, ㅝ" were used as two phonetic values. Scholars of active during this period used the notation symbol "ㅇ" to distinguish "ㅘ(wa), ㅝ(wə)" from "ㅘ(oa), ㅝ(uə)." In the result, "ㅇ" of "글왈, □오 니 " was different from the normal letter "ㅇ" as alif. This special "ㅇ" played a role as the syllable boundary. In this case, phonetic value of "ㅇ" was described as "h(voiced glottal fricative)" or "hw."