-아/어야 Grammar in Korean: Meaning and How to Use It

What you'll learn

• Attach -아/어야 with the right vowel, including contractions such as 가야 and 봐야.
• Tell a necessary condition ("only if") from a plain "if".
• Use -았/었어야 했다 for "should have".
• Connect -아/어야 to the "must" pattern -아/어야 하다.

Prerequisites: the polite ending -아요/어요 and -아/어서. Time: about 15 minutes.

Listen to two model sentences.

The next section defines the pattern.

What Does -아/어야 Grammar Mean?

-아/어야 means "only if" or "only when". A connective ending is a word ending that joins one clause to the next. This one tells the listener, "You must meet this condition first. Without it, the result will not happen."

Think of a gate. With "if", the gate may be open or closed, and the result is possible. With "only if", the gate is closed until the condition is met. 열심히 해야 성공해요 says that hard work is the way through the gate.

Logicians call this a necessary condition: it must be true for the result to follow. A sufficient condition is one that is enough by itself. Korean -(으)면 usually gives a sufficient condition, and -아/어야 gives a necessary one.

Here are two glossed examples.

The result is usually a fact or an ability: 성공해요, 살 수 있어요. It is not usually a wish or a command. When the result is "you must", Korean uses the related pattern -아/어야 하다, which has its own lesson: -아/어야 하다/되다.

The next section shows how to build the form.

How Do You Form -아/어야?

-아/어야 follows the same vowel rule as -아/어서. Remove 다 from the dictionary form to get the stem. The stem is the verb or adjective without its dictionary ending -다. Then look at the last vowel of the stem.

• If the last vowel is ㅏ or ㅗ, add 아야: 좋 + 아야 = 좋아야.
• If the last vowel is any other vowel, add 어야: 먹 + 어야 = 먹어야.
• If the verb is 하다, the result is 해야.

When the stem ends in a vowel, the two vowels often merge.

Notice that 가 + 아야 gives 가야, not 가아야. The two identical vowels merge into one. The same happens in -아/어서, where 가 + 아서 gives 가서. In speech, the final consonant of 먹, 좋 and 있 links to the vowel that follows. The ㅎ of 좋 is silent before a vowel.

Stems Ending in a Vowel

Vowel stems contract. ㅏ + 아 gives ㅏ (가야), ㅗ + 아 gives ㅘ (와야, 봐야), ㅜ + 어 gives ㅝ (줘야, 배워야), ㅣ + 어 gives ㅕ (마셔야), and ㅚ + 어 gives ㅙ (돼야). Write the contracted form. The uncontracted forms such as 보아야 are possible in careful writing, but speech uses 봐야.

Stems Ending in a Consonant

A consonant stem does not contract. Choose 아야 or 어야 by the last vowel: 먹어야, 읽어야, 좋아야, 많아야. Spoken Korean joins the final consonant to the vowel, so 읽어야 is [일거야] and 많아야 is [마나야].

Irregular Stems and Nouns

Irregular stems change as they do before -아/어서.

For nouns, use 이다, which means "to be". After a consonant, use 이어야. After a vowel, it contracts to 여야.

The next section builds a full sentence.

Worked Example: Building 열심히 해야 성공해요

Say "You succeed only if you work hard." Follow five steps.

1. Write the condition. "Work hard" is 열심히 하다. The adverb 열심히 means "hard, with effort".
2. Find the stem. Remove 다 from 하다 to get 하.
3. Add 아/어야. 하다 is a special case: 하 + 어야 contracts to 해야.
4. Write the result. "You succeed" is 성공해요 in the polite style.
5. Join the two parts. 열심히 해야 성공해요.

You'll know it worked when the first verb ends in 야 with no speech-level ending inside it, and 요 appears only once, at the end. Try the same steps with "You enter only if you have a ticket": 표가 있어야 들어갈 수 있어요.

The next section covers tense and sentence types.

Which Tenses and Sentence Types Work with -아/어야?

The tense marker sits between the stem and 야, and the speech level goes on the last verb.

Look at the past form. The marker 았/었 comes first: 가 + 았 + 어야 = 갔어야. The most useful past pattern is -았/었어야 했다, which means "should have". 그때 갔어야 했어요 means "I should have gone then." Compare 가야 했어요, which means "I had to go." The past tense has its own page: past tense -았/었-.

Yes/no questions end with a rise. A wh-question puts the stress on the question word and often ends with a fall or a rise-fall, rather than a sharp rise: 어떻게 해야 합격해요? asks "What do I have to do to pass?"

The result clause is usually a fact or an ability, and the future is shown in the result with future tense -(으)ㄹ 거예요 or future guess -겠-. A direct command after -아/어야 is unusual. For commands and wishes, use -(으)면 instead.

The next section compares -아/어야 with -(으)면.

How Is -아/어야 Different from -(으)면?

Both can be translated with "if". The difference is whether the condition is the only way or just one way.

Compare these two sentences.

• 열심히 하면 성공해요. ("If you work hard, you succeed.") Hard work is one good way, and perhaps there are others.
• 열심히 해야 성공해요. ("You succeed only if you work hard.") Without hard work, there is no success.

The English "only if" is the test. If you can say "only if" and the sentence still makes sense, use -아/어야. If you mean a plain "if" or "when", use -(으)면. For "must", move to -아/어야 하다/되다. For a deeper look at the "must" pair, see -아/어야 하다 vs -(으)ㄹ 필요가 있다.

The next section covers set phrases and edge cases.

Variations and Edge Cases of -아/어야

-아/어야 하다 and -아/어야 되다

The most common use of -아/어야 is with 하다 or 되다: 약을 먹어야 해요 ("You have to take the medicine"). The idea is the same as "only if". The sentence says that taking the medicine is the necessary step. 되다 is more colloquial than 하다.

-아/어야겠다

Adding 겠 gives a personal decision: 이제 가야겠어요 means "I should be going now" or "I'd better go". The speaker is making up their own mind.

-아/어야만

The particle 만 adds emphasis: 열심히 해야만 성공해요 means "Only if you work hard, and nothing else, do you succeed." It sounds stronger and appears in writing and speeches.

The "Should Have" Pattern

-았/었어야 했다 expresses regret. 더 공부했어야 했어요 means "I should have studied more." It usually appears with 했는데 ("but I did not"): 일찍 갔어야 했는데 늦었어요.

Question Word and Answer

-아/어야 often appears in advice questions. 어떻게 해야 해요? ("What should I do?") asks how to meet a requirement.

The next section lists the mistakes that appear most often.

What Mistakes Do Learners Make with -아/어야?

Learners make seven predictable mistakes. Each has a reason and a fix.

Learners often use it for a plain "if". Wrong: 시간이 있어야 전화하세요, when you mean "If you have time, call me". Right: 시간이 있으면 전화하세요. Fix: test with "only if". If it does not fit, use -(으)면.

Learners often use the wrong vowel. Wrong: 먹아야 and 가어야. Right: 먹어야 and 가야. Fix: look at the last vowel of the stem. ㅏ and ㅗ take 아야, and other vowels take 어야.

Learners often forget the contraction. Wrong: 가아야 and 오아야. Right: 가야 and 와야. Fix: write the contracted form when the stem ends in a vowel.

Learners often ignore irregular stems. Wrong: 춥어야 and 듣어야. Right: 추워야 and 들어야. Fix: apply the same changes you use before -아/어서.

Learners often use 가야 했어요 for regret. 가야 했어요 means "I had to go". Right for regret: 갔어야 했어요. Fix: add 았/었 before 어야 for "should have".

Learners often drop the result. Wrong: 열심히 해야. As a stand-alone ending, it is incomplete. Right: 열심히 해야 해요 or 열심히 해야 성공해요. Fix: add a result or 하다.

Learners often use it for a wish. Wrong: 돈이 있어야 사고 싶어요. Right: 돈이 있으면 사고 싶어요. Fix: the result of -아/어야 is a fact or an ability, not a feeling.

The next section gives you practice.

Practice and Answers

Do the four tasks, then compare with the key.

Task 1: join the sentences with -아/어야. Write one sentence for each pair.

1. 열심히 공부하다 / 합격할 수 있어요.
2. 일찍 일어나다 / 기차를 탈 수 있어요.
3. 표가 있다 / 들어갈 수 있어요.
4. 날씨가 좋다 / 산책할 수 있어요.

Task 2: fix the error. Each sentence has one mistake. Rewrite it correctly.

1. 약을 먹아야 나아요.
2. 날씨가 춥아야 눈이 와요.
3. 시간이 있어야 전화하세요.

Task 3: translate. Write in Korean: "You can enter only if you have a ticket." and "I should have studied more."

Task 4: write your own. Write one sentence about something you can do only if you meet a condition, and one sentence with 가야겠어요.

Answer key

1. (1) 열심히 공부해야 합격할 수 있어요. (2) 일찍 일어나야 기차를 탈 수 있어요. (3) 표가 있어야 들어갈 수 있어요. (4) 날씨가 좋아야 산책할 수 있어요.
2. (1) 약을 먹어야 나아요. (2) 날씨가 추워야 눈이 와요. (3) 시간이 있으면 전화하세요.
3. 표가 있어야 들어갈 수 있어요. 더 공부했어야 했어요. Other correct versions exist, for example 표가 있어야 입장할 수 있어요.
4. Sample answers: 친구가 도와줘야 이 일을 끝낼 수 있어요. 시간이 늦었어요. 이제 가야겠어요. Any pair is correct if the condition clause ends in 아/어야 and the result is a fact or an ability.

If task 1 was correct, you have the formation rule. If task 2 was hard, check whether you chose the right vowel and applied the irregular change. The next section points you to what comes after this lesson.

What Should You Learn after -아/어야 Grammar?

After -아/어야, learn -(ㄴ/는)다면, a hypothetical "if", and review -(으)면 if you want a plain "if" for comparison. The "must" pattern -아/어야 하다/되다 builds directly on this lesson.

For a wider view, the parent page Conditions (If) lists every connector in this group. To plan by level, use Beginner Grammar.

This lesson covers -아/어야 in the polite and casual styles. It does not cover every written variation. About this page. Last updated 2026-10-09. Revised Romanization follows the national rules and is shown only as a learning aid.

Frequently Asked Questions

What Does -아/어야 Mean?

-아/어야 means "only if" or "only when". It names a condition that has to be met before the result can happen. 열심히 해야 성공해요 means "You succeed only if you work hard." It is stronger than "if" because the condition is necessary, not just possible.

How Do I Attach -아/어야 to a Verb or Adjective?

Take the stem and look at its last vowel. After ㅏ or ㅗ, add 아야: 좋아야, 살아야. After other vowels, add 어야: 먹어야. For 하다, write 해야. A vowel stem contracts: 가 becomes 가야, 보 becomes 봐야, 주 becomes 줘야. Irregular stems change as before -아/어서: 춥다 becomes 추워야.

Can -아/어야 Be Used in the past Tense?

Yes, as -았/었어야. The best-known use is -았/었어야 했다, "should have": 그때 갔어야 했어요 means "I should have gone then." Compare 가야 했어요, which means "I had to go." The marker 았/었 goes before 어야, and the tense of the whole sentence is shown on the last verb.

Is -아/어야 Used in Speech or Only in Writing?

Both. It is common in daily speech, in polite and casual styles, especially in the set form -아/어야 해요 ("must"). It also appears in advice, instructions and news. In very formal writing, -아/어야만 adds emphasis. There is no special spoken-only or written-only version of the basic ending.

What Is the Most Common Mistake with -아/어야?

The most common mistake is using it for a plain "if". 시간이 있어야 전화하세요 does not mean "If you have time, call me". It means "Only if you have time, call me", which sounds odd. Use -(으)면 for a plain condition. Other frequent mistakes are 먹아야 and 춥아야.

What Is the Difference between -아/어야 and -(으)면?

-(으)면 says that something happens when the condition is true: 돈이 있으면 살 수 있어요. -아/어야 says that the condition is the only way: 돈이 있어야 살 수 있어요, "You can buy it only if you have money." The result after -(으)면 can be any sentence type. After -아/어야 it is usually a fact or ability.