어야

• -아야
• -아야지/어야지

-—어야 • (--eoya)

1. Only when ... (A connective ending used when the preceding statement is an essential condition for the following statement.)

   건강하게 먹어야 행복하게 산다. (Geon-ganghage meogeoya haengbokhage sanda., “You live happy only when you eat healthy.”)

2. Even when ... (A connective ending used when the preceding assumption has no influence in the end.)

   길어야 1년을 안 넘길 테니 걱정할 것 없어. (Gireoya 1nyeoneul an neomgil teni geokjeonghal geot eopseo., “You don't have to worry since it won't take more than a year even when the longest.”)

The suffix -아야 (aya)/어야 (eoya) can convey the meaning of duty and obligation when in collaboration with verb 하다 (hada) or 되다 (doeda), thus might be translated to "must", "should", "have to", and so forth. → 어야 하다

E.g. 하지만 공부해야 되는데···. (Hajiman gongbuhaeya doeneunde···., “but I have to study....”)

Also, the form -아/어야( 하)겠다 (a/eoya( ha)getda) is commonly used for weak volition of the speaker.

E.g. 이제 좀 쉬어야겠다. (Ije jom swieoyagetda., “Now I'm gonna take some rest.”)

This suffix is attached to the infinitive form. 이르다(이르러) (ireuda(ireureo), “to arrive”) → 이르러야 (ireureoya, “only when arriving”)

• National Institute of Korean Language (CC BY-SA 2.0 KR)