🇰🇷 Lesson 19: Can, Must & May: Ability, Obligation, Requests

So far you can say what you do, what you did, and what you want or plan to do. But real life is full of can, can't, have to, may I…? and please…. Can you drive? Do you have to work tomorrow? May I take a photo here? Could you speak slowly? This lesson gives you the handful of patterns that answer all of those questions.

Here is the mental model to hold on to: English uses little helper words (can, must, may) in front of the verb. Korean attaches an ending to the verb stem and then adds a small "support verb" after it. The meaning lives in the ending plus that support verb — 있다 (there is), 하다/되다 (do / be OK), 안 되다 (not OK). Once you see that each pattern is literally built from words you already know, they stop feeling like new vocabulary and start feeling like logic.

💪 Part 1 — Ability: -(으)ㄹ 수 있다 / 없다

The word 수 means "way, means, possibility". So 갈 수 있어요 is literally "a way to go exists" → I can go. Swap 있어요 for 없어요 and you get I can't go. You already know 있어요/없어요 from Lesson 9 — the only new piece is the -(으)ㄹ ending that hooks the verb onto 수.

Tense goes on the final 있다/없다, not on the verb in front: 갈 수 있었어요 "I was able to go", 갈 수 없었어요 "I couldn't go". The verb before 수 never changes.

수 없다 vs 못 — what's the difference?

In Lesson 10 you met 못 ("can't"). 못 가요 and 갈 수 없어요 both mean "I can't go", and in most everyday sentences they are interchangeable. As a rough guide, 못 is short and conversational, while 수 없다 sounds a little fuller and is common for circumstances and rules ("You can't park here"). Neither is wrong.

잘하다 / 못하다 — being good or bad at something

For skills, Koreans very often skip "can" and talk about how well you do it. 잘하다 = to be good at, 못하다 = to be bad at / unable to do. The skill takes the object particle 을/를.

🇰🇷 Cultural note — the modesty reflex. If you say even two words of Korean, expect to hear 한국어를 잘하세요! ("You speak Korean well!"). The expected reply is not "thank you" but polite modesty: 아니에요, 아직 잘 못해요. ("Not at all, I'm not good yet.") Accepting a compliment too directly can sound a little boastful. Deflecting it is a social ritual, and now you have the grammar to play along.

📌 Part 2 — Obligation: -아야/어야 하다 (되다)

The ending -아야/어야 means "only if (you) do". Follow it with 해요 or 돼요 and you get have to / must: 가야 해요 = "(only if I go, it works) → I have to go".

하다 or 되다? They mean the same thing. 해야 돼요 is extremely common in everyday speech; 해야 해요 is slightly more neutral and is what you'll see more in writing. Use whichever sounds natural to you — both are correct.

"Don't have to": -지 않아도 되다 / 안 -아도 되다

Here's a trap for English speakers: "you must not go" and "you don't have to go" are very different. Korean keeps them apart with different patterns. "Don't have to" is literally "even if you don't do it, it's fine":

That "even if…, it's fine" shape is the permission pattern — which is exactly Part 3.

✅ Part 3 — Permission & Prohibition

May I…? -아도/어도 되다

-아도/어도 means "even if (you) do". Add 돼요 ("it's OK") and you get "it's OK to / you may". Turn it into a question for "May I…?" Same trick as before: -아요/어요 form, drop 요, add 도.

Must not: -(으)면 안 되다

-(으)면 means "if". So -(으)면 안 돼요 is "if you do it, it's not OK" → you must not / you're not allowed to. You will see this on signs everywhere in Korea.

🙏 Part 4 — Asking Others: Requests & Commands

-(으)세요 — "please do"

Good news: you already know this one. In Lesson 13 you learned the honorific -(으)시- and its polite form -(으)세요. Said to someone about their own action, it becomes a gentle, respectful instruction: 앉으세요 "Please sit." It's what shop staff, teachers and hosts say all day long.

Remember the special honorific verbs from Lesson 13: you say 드세요, never 먹으세요, and 주무세요, never 자세요, to someone you're being polite to.

-지 마세요 — "please don't"

To ask someone not to do something, attach -지 to any stem and add 마세요 (from 말다, "to stop, refrain"). No vowel harmony, no 으 — the easiest ending in this lesson.

-아/어 주세요 — "please do it (for me)"

주다 means "to give". -아/어 주세요 literally says "do it and give (the favour) to me". It turns a command into a request for a favour, so it feels warmer than a bare -(으)세요. Build it from the -아요/어요 form again: drop 요, add 주세요.

-아/어 줄래요? — "will you…?"

Turning the request into a question makes it softer still. -아/어 줄래요? ("will you do it for me?") is friendly and polite — ideal with friends, classmates and colleagues around your age. For strangers and elders, the extra-polite -아/어 주시겠어요? ("would you kindly…?") is useful to recognise: 창문 좀 열어 주시겠어요?

(열다 is an ㄹ-stem, which is why its -(으)세요 form is 여세요 — you'll see exactly why in Lesson 21.)

🇰🇷 Cultural note — the magic of 좀. Notice the little word 좀 ("a bit") in so many requests. It doesn't really mean "a little" here; it's a softener, like English "just" in "Could you just…". Koreans also often open a request with 죄송하지만 ("I'm sorry, but…") (a set phrase — the -지만 'but' ending comes in Lesson 23) or 저기요 ("excuse me") to get attention. A request with 좀 and 주세요 sounds considerate; a bare command can sound blunt even when it's grammatically polite.

💬 Dialogue — At the Palace Museum

Emma is visiting a museum in Seoul and talks to a staff member (직원).

Count them: permission, prohibition, obligation, "don't have to", a favour request, a polite command, a "please don't", and ability — the whole lesson in eight lines.

If these endings blur together at first, that's normal — they all reuse the same -아/어 stem you already know, so your brain is sorting similar shapes. Each mix-up you notice is feedback that the sorting is happening. You don't have it "wrong"; you just don't have it yet.

✍️ Practice

🧠 Check Your Understanding

❓ Common Questions

🔮 Looking Ahead

In Lesson 20: Health & Body you'll put these patterns straight to work at the doctor's and the pharmacy — "Where does it hurt?", "You have to rest", "You mustn't drink alcohol", "Please take this medicine". Then Lesson 21 finally explains the "odd" forms you may have noticed, like 여세요 from 열다 and 도와주세요 from 돕다: Korean's irregular verbs.