The expression can or cannot do in Korean is made using the pattern plain base+ (으)ㄹ 수 then 있어요 (isseoyo) or 없어요 (opseoyo). This verb ending literally means ‘ a means exists’ or ‘a means do not exists’. Here are examples:
- 볼 수 있어요 (bol su isseoyo) can [I/we] see
- 쓸 수 있어요 (seul su isseoyo) can write or can use
- 걸을 수 없어요 (keoreul su opseoyo) can’t walk
- 갈 수 없어요 (kal su opseoyo) can’t go
The behavior is the same as that of the verb ending for probable future (으)ㄹ 거에요 (eu0l koeyo) where l-extending verbs remains unextended when the attached as such:
살다 (to live) is transformed to 살 수 없어요 (sal su opseoyo) to mean can’t live. 살 in this form is actually 사 (unextended form)+ ㄹ (the modifier in the verb ending).
It Started with Hangul 