Core Pattern Rule: Expressing Obligation with -아야/어야 해
This pattern expresses obligation, necessity, or a strong intention, similar to "have to" or "must" in English. It's attached to verb stems to state that an action is required.
Formation Rules
Vowel ㅏ or ㅗ: If the last vowel of the verb stem is ㅏ or ㅗ, you add -아야 해.
가다 (to go) → 가 + 아야 해 → 가야 해
보다 (to see) → 보 + 아야 해 → 봐야 해 (vowels combine)
Other Vowels: For all other verb stems, you add -어야 해.
먹다 (to eat) → 먹 + 어야 해 → 먹어야 해
듣다 (to listen) → 듣 + 어야 해 → 들어야 해 (ㄷ irregular)
하다 Verbs: Verbs ending in 하다 change to 해야 해.
공부하다 (to study) → 공부해야 해
일하다 (to work) → 일해야 해
나 지금 집에 가야 해. / 병원에 가야 해. / 공부해야 해. / 일찍 일어나야 해.
Synonyms & Differences: 해 vs. 돼 vs. 하다
In conversation, you'll hear variations of this pattern that are often interchangeable but have subtle differences in nuance.
-아야/어야 해
This is the most common form in everyday speech. It feels personal and direct, expressing the speaker's own feeling of obligation or a direct suggestion to a listener.
Usage: Best for personal statements or talking with friends.
Example: 이건 꼭 사야 해. (I really have to buy this. - my own strong feeling)
-아야/어야 돼
This is also extremely common in spoken Korean and is often used interchangeably with 해. 돼 comes from 되다 (to become, to be okay), so it can carry a slightly softer nuance, implying that an action is necessary for a situation to work out or be acceptable. The difference is often minimal.
Usage: Interchangeable with 해 in most daily conversations.
Example: 돈을 내야 돼. (The money has to be paid. - for the transaction to be complete)
-아야/어야 하다
This is the dictionary form and sounds more formal, objective, or literary. It's used more in writing, news reports, or formal presentations to state a general rule or fact rather than a personal feeling.