Must/Only If (-아/어야)
-아/어야
Expresses a necessary condition, meaning 'must' or 'only if'.
Pattern
Verb/Adjective stem + -아/어야 + Result clause
Explanation
-아/어야 expresses that the first clause is a necessary condition for the second clause to occur. It means 'only if' or 'must... in order to'. The form follows vowel harmony: -아야 after ㅏ/ㅗ, -어야 after other vowels, and 해야 for 하다 verbs.
For example, 열심히 공부해야 시험에 합격해요 means 'Only if you study hard will you pass the exam.' The condition is presented as essential, not merely possible. This is stronger than -(으)면, which presents a general condition.
When combined with 하다 or 되다, it forms the obligation pattern -아/어야 하다/되다 (must, have to), which learners encountered at Level 2. At Level 3, the focus is on using -아/어야 independently as a connective ending to express prerequisite conditions.
Examples
열심히 공부해야 시험에 합격해요.
Yeolsimhi gongbuhaeya siheome hapgyeokhaeyo.
Only if you study hard will you pass the exam.
돈이 있어야 살 수 있어요.
Doni isseoya sal su isseoyo.
You can only buy it if you have money.
건강해야 행복해요.
Geonganghaeya haengbokhaeyo.
You can only be happy if you're healthy.
직접 가 봐야 알 수 있어요.
Jikjeop ga bwaya al su isseoyo.
You can only know by going there yourself.
Common Mistakes
Wrong
열심히 공부하면 합격해요.
Correct
열심히 공부해야 합격해요.
-(으)면 expresses a general 'if', while -아/어야 emphasizes that the condition is necessary and required.
Wrong
돈이 있어야만 살 수 있어요.
Correct
돈이 있어야 살 수 있어요.
Adding 만 (only) to -아/어야 is possible but redundant, as -아/어야 already implies 'only if'.
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