quality:corruption, linguistic:paraphrasing, structural:reformatting, stylistic:style_transfer
Compound vowels

The Korean alphabet does not have a letter for w sound. Since an o or u before an a or eo became a sound, and occurred nowhere else, could always be analyzed as a phonemic o or u, and no letter for was needed. However, vowel harmony is observed: dark ㅜ u with dark ㅓ eo for ㅝ wo; bright ㅗ o with bright ㅏ a for ㅘ wa:

The compound vowels ending in ㅣ i were originally diphthongs. However, several have since evolved into pure vowels: