should, must, have to
In this expression, the preceding clause states the condition(s) necessary to realize the situation stated in the following clause.
1. To emphasize the meaning of -아/어야, either -지 can be added to form -아/어야지 or 만 can be added to form -아/어야만. Note, however, that -아/어야지 is generally used in casual conversation while -아/어야만 is generally used in speeches and reports.
2. The clause following this expression cannot be in a propositive or imperative form.
3. Because this expression indicates a conditional statement, the past tense cannot be used in the following clause.
4. The expressions 이어야/여야 and 이라야/라야 can also be used as 이/가 아니어야 and 이/가 아니라야 respectively.
5. This expression can also be used to indicate the futility of expecting the result described in the following clause regardless of what action is described in the preceding clause.
Express a necessity, obligation or a condition that has be completed for something else to realize.