In short

To make an “if / when” clause, attach -(으)면 to the stem of the condition and put that clause first: -면 after a vowel or a ㄹ-stem (가면 gamyeon, if one goes; 살면 salmyeon, if one lives), and -으면 after a 받침 (먹으면 meogeumyeon, if one eats). The one ending covers both a real condition (if…) and a general or habitual truth (whenever…), and the condition clause stays in the plain present even when the event is still in the future.

The rule

Step 1 - The condition clause comes first, with -(으)면 on its stem

The frame is Condition + -(으)면, Result. The ending goes on the verb or adjective stem of the if-clause, and the main clause that follows carries the real tense and mood of the sentence: 비가 오면 집에 있어요 (biga omyeon jibe isseoyo, if it rains, I stay home). There is nothing between the stem and -(으)면.

Step 2 - Pick the allomorph by the 받침

This is one of the ordinary -(으)- endings from lesson 17: a bare -면 after a vowel stem, -으면 after a stem that ends in a 받침. A ㄹ-stem behaves like a vowel stem - it drops the 으 but keeps its ㄹ, because 면 begins with ㅁ (not ㄴ, ㅂ or ㅅ): 살다 -> 살면 (salmyeon), 만들다 -> 만들면 (mandeulmyeon). Never *살으면.

Step 3 - Irregular stems change first

Because the 으 makes this a vowel-type ending, the ㅂ, ㄷ and ㅅ classes fire before it: 덥다 -> 더우면 (deoumyeon, if it’s hot), 듣다 -> 들으면 (deureumyeon, if one listens), 짓다 -> 지으면 (jieumyeon, if one builds). The 르 and 으 stems, on the other hand, do not change here - they need a following 아/어, which -(으)면 does not have: 모르다 -> 모르면 (moreumyeon), 쓰다 -> 쓰면 (sseumyeon). The ㅎ class (lesson 39) goes further and swallows the 으 whole: 그렇다 -> 그러면 (geureomyeon).

Step 4 - -(으)면 is both “if” and “whenever”

The same ending marks a hypothetical condition (if X happens) and a general or habitual truth (whenever X, Y): 봄이 되면 꽃이 피어요 (bomi doemyeon kkochi pieoyo, when spring comes, flowers bloom). Context decides which reading you get. For a single, specific point in time (when I arrived…) you want -(으)ㄹ 때 instead, coming in lesson 30.

Step 5 - Keep the condition clause in the plain present

Even when the if-event lies in the future, do not stack a future marker inside the 면-clause. English “call me when you will arrive” becomes plain 도착하면 전화하세요 (dochakamyeon jeonhwahaseyo, call me when you arrive), not 도착할 거면 - that is a different sentence, if you’re planning to arrive. The main clause is where tense lives.

Step 6 - The -(으)면 pattern family

Three high-frequency combinations build on the same ending. -(으)면 되다 means it’s enough to / you just have to: 누르면 돼요 (nureumyeon dwaeyo, just press it). -(으)면 좋다 means it’s good if: 싸면 좋아요 (ssamyeon joayo). Adding past -았/었- gives -았/었으면, a hypothetical or counterfactual flavour (if it had…); on the counterfactual reading the result clause goes past with it, as -았/었- + -을 거예요: 갔을 거예요 (gasseul geoyeyo, would have gone), 좋았을 거예요 (joasseul geoyeyo, would have been good). The full if only template -았/었더라면 … -았을 텐데 waits in lesson 61. You can also flag the “if” early with 만약(에) or 만일(에) - but these adverbs never replace the ending; the -(으)면 still does the grammatical work: 만약 비가 오면… (manyak biga omyeon…, if it rains…).

Forms & patterns

The core allomorph table - what attaches to what:

Irregular stems before -(으)면 (it is an -(으)- ending, so the stem changes first):

The -(으)면 pattern family:

Examples

Common mistakes

• 먹면 (meongmyeon) -> 먹으면 (meogeumyeon) - after a 받침 the ending is -으면, never a bare -면. If one eats.
• 만드면 (mandeumyeon) -> 만들면 (mandeulmyeon) - a ㄹ-stem keeps its ㄹ before -면 (면 starts with ㅁ, not ㄴ/ㅂ/ㅅ); only the 으 is dropped. If one makes.
• 도착할 거면 전화하세요. (Dochakal geomyeon jeonhwahaseyo.) -> 도착하면 전화하세요. (Dochakamyeon jeonhwahaseyo.) - for a plain future event the condition clause stays in the present. (도착할 거면 is itself well formed - 거 + -(이)면 - but it means if you’re planning to arrive, not when you arrive.)
• 덥으면 (deobeumyeon) -> 더우면 (deoumyeon) - 덥다 is ㅂ-irregular, so the ㅂ becomes 우 before the 으 of -(으)면. If it’s hot.

Tips

• One form, two jobs. -(으)면 is both if (a hypothetical condition) and whenever (a general or habitual truth). For a single, specific moment - when I arrived, when I was a child - reach for -(으)ㄹ 때 (lesson 30) instead.
• Keep the future out of the if-clause. Say 도착하면, not 도착할 거면 (if you’re planning to). Korean marks tense once, in the main clause; the condition clause looks present even when it points at tomorrow.
• 만약 is only a signpost. 만약(에) or 만일(에) at the front warns the listener “a condition is coming”, but you still need -(으)면 on the verb - the adverb can never carry the “if” by itself.
• Sufficient vs necessary, and wishes. -(으)면 is a plain if; for only if / you have to, use -아/어야 (lesson 34). And to say I wish / I hope that…, the pattern -(으)면 좋겠다 waits in lesson 61.