Explanation 5 · Three-Sound Harmony

Checked tone to softer final sounds

    The semi-tongue sound ㄹ (R/L) is used in native Korean
    words but is not found in Hanja. For example, the Hanja
    character with the sound of 볃 ByeoT preserves the checked
    tone with the final sound ㄷ(iD). However, over time,
    people habitually softened the final sound ㄷ in Hanja
    pronunciation, replacing it with the lighter ㄹ sound, leading
    to 별 ByeoL.
    As a result, while 볃 ByeoT retains its checked tone, 별
    ByeoL has lost this quality, as its sound spreads and slows
    down, preventing it from functioning as an entering-tone
    syllable.




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