-(으)면 — conditional and 'whenever'
-(으)면 is the all-purpose 'if / when (whenever)' ending. Glue it onto the verb stem of the condition clause. 시간이 있으면 갈 거예요. = 'If I have time, I'll go.' 비가 오면 우산을 써요. = 'When it rains, I use an umbrella.' Korean uses the SAME ending for hypothetical 'if' and habitual 'whenever' — context (and the final verb) tells you which. The shape choice is straightforward: vowel-ending stem → -면, consonant-ending stem → -으면.
Shape choice: -면 vs. -으면
Look at the LAST letter of the verb stem (after dropping -다). If it ends in a vowel, attach -면 directly. 가다 → 가면 (if/when go). 오다 → 오면. 공부하다 → 공부하면. If it ends in a consonant, insert 으: -으면. 있다 → 있으면. 먹다 → 먹으면. 읽다 → 읽으면. The exception you'll meet: stems ending in ㄹ drop the 으 because ㄹ already 'counts' as connectable: 살다 → 살면, 알다 → 알면, 만들다 → 만들면.
Conditional 'if' — the most common use
Use -(으)면 to set up an unfinished or hypothetical condition for what comes next. The future, command, or suggestion lives in the second clause. 시간이 있으면 도와주세요. = 'If you have time, please help.' 돈이 있으면 새 컴퓨터를 살 거예요. = 'If I have money, I'll buy a new computer.' 피곤하면 자요. = 'If you're tired, sleep.' Notice you don't put past tense on the -(으)면 clause when it's an open condition — 있으면, not 있었으면 (the -았/었으면 form means 'if only…' / counterfactual, which is a separate construction).
Habitual 'when / whenever'
Same ending, but the second clause is a present-tense general statement → 'whenever': 비가 오면 우산을 써요. = 'When(ever) it rains, I use an umbrella.' 봄이 오면 꽃이 펴요. = 'When spring comes, flowers bloom.' 저는 피곤하면 커피를 마셔요. = 'When I'm tired, I drink coffee.' English splits 'if' (one-time, hypothetical) from 'whenever' (habitual) but Korean leaves it to context — the present-vs-future shape of the second verb does the work.
Negative conditions
To say 'if (you) don't…', negate the verb in the -(으)면 clause. With 안: 시간이 있으면 → 시간이 없으면 ('if you don't have time'). 밥을 안 먹으면 배고파요. = 'If you don't eat, you get hungry.' Or use the negative-existence verb directly: 없다 + -으면 → 없으면. With long negation -지 않다: 공부하지 않으면 시험을 못 봐요. = 'If you don't study, you can't take the test.' Either approach is fine.
Common formula sentences
Some patterns are worth memorizing as units. 괜찮으면 = 'if (it's) okay' — the standard polite hedge: 괜찮으면 같이 가요. = 'If it's okay, let's go together.' 시간 있으면 = 'if you have time' — perfect for casual invites. 싫으면 말아요. = 'If you don't want to, never mind.' Conditional -(으)면 also pairs nicely with the future -(으)ㄹ 거예요 you've already seen: 내일 비가 오면 안 갈 거예요. = 'If it rains tomorrow, I won't go.'
