STEP 5 • The Case of the 4 Missing Letters
580 years ago, Koreans wrote
mystery letters in their hearts
Of Sejong's 28 letters, only 24 remain. Who's the culprit? Not vandals — 500 years of sound evolution. Open the case files now.
ㆍ
용의자 01[ʌ / ɒ]
Arae-a
Died 16th–18th c.
A yang vowel born of the round sun. It split into "ㅡ" and "ㅏ" and vanished — but still lives on Jeju Island ("혼저옵서예").
The residue • still alive today
Rediscovered today in brands & fonts as a Korean icon
ᅀ
용의자 02[z]
Banchieum
Died late 16th c.
A voiced [z] like in English. It weakened between vowels until it went silent — creating today's tricky "ㅅ-irregular" verbs.
The residue • still alive today
The hidden culprit behind "ㅅ-irregular" verbs
ㆁ
용의자 03[ŋ]
Yesieung (아래 "ㅇ" 받침)
Lost as an initial sound → merged 1933
Modern "ㅇ" is silent at the start of a syllable, but 580 years ago it hummed [ŋ] even there. Today it survives as the final sound of 방, 강, 사랑.
The residue • still alive today
Alive in every final "ㅇ" (강, 방, 사랑)
ㆆ
용의자 04[ʔ]
Yeorinhieut
Died first, late 15th c.
The catch in "uh-oh" [ʔ]. So rare in daily speech it retired first, 50 years after birth. It's still the reason "…할 것을" is pronounced "…할꺼슬".
The residue • still alive today
The reason behind tensing in "[할꺼슬]"