Grammar
-아/어야 하다
Necessity or obligation
Form
Verb or adjective root + -아/어야 하다 — « must / should ... »
Function
-아/어야 하다 means "to have to / one must" ».
Why this form?
-아/어야 되다 is often similar, but a little more conversational
(ex : 지금 가야 돼요. — I have to go now.)
-(으)면 좋겠다 expresses a wish or a suggestion, not an obligation.
(ex : 지금 가면 좋겠어요. — It would be nice to leave now.)
Examples
나가야 한다. — We need to go out.
여기서 기다려야 합니다. — You have to wait here.