Want & Can: ~고 싶다, ~(으)ㄹ 수 있다
Express what you want to do and what you are able to do.
Expressing desire and ability in Korean unlocks a huge range of natural conversation. -고 싶다 attaches to a verb stem to mean 'want to': 가다 (go) → 가고 싶다 (want to go) → 가고 싶어요 (polite: I want to go). The pattern is identical for any verb.
-(으)ㄹ 수 있다 / 없다 expresses ability: 하다 → 할 수 있어요 (I can do it) / 할 수 없어요 (I cannot do it). The (으) appears after consonant-ending stems for euphony. The phrase 수 있다 literally means 'there is a way', which is a natural way to express possibility in Korean. Note the contrast with 못 from Lesson 3-4: -(으)ㄹ 수 없다 is a softer way of saying 'cannot', while 못 is more direct. In conversation, Koreans often soften refusals using 못 하겠어요 or 못 할 것 같아요 instead of a flat 안 해요, which can sound rude.
~고 싶다 — Want to do
Attach 고 싶다 to the verb stem (remove 다). 가다 → 가고 싶어요 (I want to go). For past: 고 싶었어요 (I wanted to).
~(으)ㄹ 수 있다/없다 — Can / Cannot
Verb stem + (으)ㄹ 수 있다 = can do. If stem ends in consonant → 을 수 있다, vowel → ㄹ 수 있다. Replace 있다 with 없다 for 'cannot'.
Cultural & Language Note
고 싶다 can only describe your own desire in a plain statement. To talk about what someone else wants, Korean switches to 고 싶어하다 — a grammatical acknowledgement that you cannot directly know another person's inner state. Japanese does exactly the same thing with たい versus たがる, so this rule needs no explanation for Japanese speakers.
Common Mistakes to Avoid
Saying 친구가 가고 싶어요 to mean 'my friend wants to go' is the standard error; it needs 가고 싶어해요. For 을 수 있다, remember it expresses ability or possibility, while 못 expresses a blocked attempt — 갈 수 없어요 and 못 가요 overlap but are not identical in nuance.