할 수 있다 for Every 'Can'

English can is one word doing three jobs: ability ("I can swim"), permission ("can I go?"), and polite request ("can you help me?"). Learners map all three onto the one Korean structure they know for "can," -(으)ㄹ 수 있다, and produce misfires like ×창문을 열 수 있어요? to ask someone to open a window, or ×화장실에 갈 수 있어요? for "can I go to the bathroom?" Korean does not bundle these meanings — it lexicalizes each with a different grammar. Ability/possibility is -(으)ㄹ 수 있다; permission is -아/어도 되다; a request is -아/어 주세요 (or the more deferential -아/어 주시겠어요?). Split "can" into three, and each maps cleanly.

Why the English brain does this

English collapses three distinct speech acts into can. "I can eat spicy food" reports a capability. "Can I sit here?" asks for permission. "Can you pass the salt?" is a request dressed as a question about ability. English speakers barely notice these are different — the same modal covers all three — so when a learner meets -(으)ㄹ 수 있다 glossed as "can," they naturally pour every "can" into it. The leak shows up most where -(으)ㄹ 수 있다 sounds oddly literal: asking ×창문을 열 수 있어요? literally questions whether the listener is physically capable of opening the window, which is not a polite request — it's almost a challenge.

The cure is to feel the three meanings as separate and reach for a different structure for each.

Ability / possibility: -(으)ㄹ 수 있다

This is the only job -(으)ㄹ 수 있다 does: stating that something is possible or that you have the ability to do it. Its negative is -(으)ㄹ 수 없다 (or 못). Allomorphy: -을 수 있다 after a batchim, -ㄹ 수 있다 after a vowel.

For a skill you've learned — driving, swimming, speaking a language — Korean often prefers -(으)ㄹ 줄 알다 ("know how to"), which is even more idiomatic than 수 있다:

The two ability structures are compared on the -(으)ㄹ 수 있다 page and the -(으)ㄹ 줄 알다 page. Neither is used for permission or requests.

Permission: -아/어도 되다

"Can I…? / May I…? / Is it OK to…?" is -아/어도 되다 — literally "even if I do X, it's fine." This is the permission slot, and it is where learners most often wrongly reach for 수 있다.

The answer to a permission question is 네, 돼요 ("yes, that's fine") or 아니요, 안 돼요 ("no, you can't"). Asking ×화장실에 갈 수 있어요? instead means "am I physically able to go to the bathroom?" — which is not what you're asking. The permission construction is detailed on the -아/어도 되다 page.

Request: -아/어 주세요 (or -아/어 주시겠어요?)

"Can you open the window? / Could you help me?" is a request, and Korean makes requests with the benefactive -아/어 주세요 ("please do X for me"). For extra politeness, -아/어 주시겠어요? ("would you kindly do X?") climbs the deference ladder.

That little 좀 ("a bit") is the politeness lubricant that makes a request sound gracious rather than curt. Framing a request as ×창문을 열 수 있어요? ("are you able to open the window?") sounds like you're testing the listener's strength, not asking a favor. The request ladder from 주세요 up to 주시겠어요 is on the 주세요 page and the request-ladder page.

The three-way map

Common Mistakes

Every error is one "can" being forced through -(으)ㄹ 수 있다 when it should be a different structure.

1. ×창문을 열 수 있어요? for "can you open the window?" That's a request → -아/어 주세요.

2. ×화장실에 갈 수 있어요? for "can I go to the bathroom?" That's permission → -아/어도 되다.

3. ×한국어를 말할 수 있어요 as the default "I can speak Korean." For a language skill, drop 말하다 and use 하다 (or -ㄹ 줄 알다).

4. Using 수 있다 to grant/refuse permission. "You can't (do that)" as a rule is 안 돼요, not 수 없다.

Key Takeaways

• English can = three Korean structures. Ability/possibility → -(으)ㄹ 수 있다 (수영할 수 있어요); for learned skills, -(으)ㄹ 줄 알다.
• Permission ("may I / is it OK?") → -아/어도 되다 (앉아도 돼요?), refused with 안 돼요.
• Request ("can you…?") → -아/어 주세요 (창문 좀 열어 주세요), or deferential -아/어 주시겠어요?.
• The tell-tale symptom: -(으)ㄹ 수 있다 in a permission or request slot literally questions someone's physical capability, which sounds like a challenge, not politeness.
• Split "can" into ability / permission / request before you translate, and the ability vs permission vs request structures each fall into place. See also 못 vs -(으)ㄹ 수 없다 for negating ability.