One ending, two big jobs: concession and permission
Take any verb stem, attach -아도 (after ㅏ/ㅗ stems) or -어도 (after other stems), and you've made an 'even if / even though' clause: 비가 와도 갈 거예요. ('Even if it rains, I'll go.'). Add 되다 ('to become / be okay') and the same shape becomes a permission: 들어와도 돼요. ('You may come in.'). Same connector, two different worlds — concession when it stands alone, permission when 되다 follows.
Forming -아/어도
It's the regular -아/어 family. Stems ending in ㅏ or ㅗ take -아도: 가다 → 가도, 오다 → 와도, 보다 → 봐도. Other stems take -어도: 먹다 → 먹어도, 읽다 → 읽어도, 마시다 → 마셔도. 하다 verbs become 해도: 공부하다 → 공부해도. Past tense pushes -았/었- in front: 갔어도 ('even though I went'). Adjectives work too: 비싸다 → 비싸도 ('even though it's expensive').
Concession: 'even if / even though'
On its own, -아/어도 sets up a contrast: the second clause happens regardless of the first. 비가 와도 갈 거예요. ('Even if it rains, I'll go.') 피곤해도 운동해요. ('Even though I'm tired, I exercise.') 아무리 바빠도 전화는 받아요. ('No matter how busy, I answer the phone.') The intensifier 아무리 ('no matter how') often pairs with this ending.
Permission: -아/어도 되다
Glue 되다 ('to be okay') onto -아/어도 and you've granted permission — literally 'even if you do X, it's okay'. Polite: 들어가도 돼요. ('You may go in.'). Question: 여기 앉아도 돼요? ('May I sit here?'). Past: 봤어도 돼요? is wrong — for past permission you say 이미 봐도 됐어요 is awkward; instead use 봐도 됐어요 rarely; everyday Korean simply uses present. Negative permission ('you may not') is handled with -(으)면 안 되다 — covered later.
괜찮다 as a stand-in for 되다
괜찮다 ('to be okay, fine') replaces 되다 with a softer feel: 먹어도 괜찮아요. ('It's okay if you eat it.'). Same construction. You'll also hear 좋다 ('good') sometimes: 그렇게 해도 좋아요. ('It's fine to do it that way.') — slightly more formal.
Reading the contrast
When you hear -아/어도 without 되다 in the next breath, expect a contrast: 'even if A, B'. When you hear -아/어도 돼요? with rising intonation, it's a request for permission. Native speakers also tack -아/어도 onto questions for casual checking: 이거 먹어도 돼? ('Can I eat this?' — to a friend, in 반말).
