In English, "can" is a single word. In Korean, expressing ability uses a fixed pattern:
Verb stem + ㄹ/을 수 있다: can, am able to Verb stem + ㄹ/을 수 없다: cannot, am not able to
수 literally means "way" or "method." The pattern says: "there exists a way to [do verb]."
Forming it
For verbs ending in a vowel: add ㄹ 수 For verbs ending in a consonant: add 을 수
| Verb | Stem | Polite form |
|---|---|---|
| 가다 (go) | 가 (vowel) | 갈 수 있어요 |
| 먹다 (eat) | 먹 (consonant) | 먹을 수 있어요 |
| 마시다 (drink) | 마시 (vowel) | 마실 수 있어요 |
| 읽다 (read) | 읽 (consonant) | 읽을 수 있어요 |
| 하다 (do) | 하 (vowel) | 할 수 있어요 |
In sentences
한국어를 할 수 있어요. I can speak Korean. 수영을 할 수 없어요. I can't swim. 지금 올 수 있어요? Can you come now? 내일까지 끝낼 수 있어요. I can finish by tomorrow.
Past ability
Add past tense to 있다/없다:
갈 수 있었어요. I was able to go. 갈 수 없었어요. I wasn't able to go.
A more natural "can't": ~못
In spoken Korean, 못 (mot) is more commonly used than ~ㄹ/을 수 없다 for expressing inability.
못 comes before the verb:
못 가요. I can't go. (spoken, natural) 갈 수 없어요. I can't go. (slightly more formal/emphatic)
Both are correct. 못 feels more immediate; ~ㄹ/을 수 없다 feels more deliberate.
Permission vs ability
~ㄹ/을 수 있다 covers both ability ("I am capable of") and possibility ("it is possible to"). For permission specifically, Korean uses ~아/어도 되다:
여기 앉아도 돼요? May I sit here? (permission) 여기 앉을 수 있어요? Can I sit here? (ability/possibility: slightly ambiguous)
In casual speech, Koreans use 있어요? for both. In formal situations, use 돼요 for permission.
Combining with ~고 싶다
These two patterns combine naturally:
한국에 가고 싶은데 갈 수 없어요: I want to go to Korea but I can't.
영화를 보고 싶으면 지금 볼 수 있어요: If you want to watch a movie, you can watch now.
This pattern is building-block grammar. Once you have it, dozens of other expressions open up. Track your progress through ability patterns with a structured Korean course's structured grammar curriculum, which sequences patterns in the order they build on each other.