Hangul vowel O

Same vowel, different encoded forms.

Hangul builds syllables by combining jamo, its letter components. ᅩ is the vowel in the middle position; ㅗ is its compatibility-jamo counterpart. They mark the same Korean vowel, but software can treat the encoded forms differently.

On a Korean 2-set (Dubeolsik) keyboard, H enters ㅗ in Hangul mode; the input method (IME) combines jamo into syllable blocks. Use ᅩ when exact conjoining-form identity matters.

Why does ᅩ combine with other vowels?

It is one part of Hangul’s original vowel design.

Hangul’s original vowel forms use ㆍ (a dot), ㅡ (a horizontal line), and ㅣ (a vertical line). ㅗ puts the dot above ㅡ; ㅛ uses two dots in the same pattern. Hunminjeongeum, the text that introduced Hangul, is dated 1443; its explanatory book was published in 1446. The preface presents it as a way to write the speech of Joseon, the Korean kingdom of the time; the book explains each sound and the first, middle, and final positions in a syllable. This is a designed letterform, not an older picture sign gradually turned into a vowel.

In Middle Korean, an older stage of the language, ᅩ belonged to the wide-vowel group in vowel harmony, a pattern that favored certain vowels together. By early modern Korean, a later period, harmony had weakened and some alternations had settled into separate word forms. In a modern conjoining-jamo sequence, ᅩ followed by ᅡ forms ᅪ.