Should, must, have to + do
We have only 1 word for those in Korean.
해야 하다 = should do,must do, have to do
but we can use adverb to emphasize it as must, have to ..
해야 하다/한다 = should do
해야만 하다/한다 = have to do, must do
꼭 해야 하다/한다 = have to do, must do
꼭 해야만 하다/한다 = have to do, must do
해야 했다 = should have done.
1. when verb ended as consonant + 다 as 먹다(머+ㄱ+다) -> 먹+어야
저녁을 먹어야 해 : I should eat dinner
저녁을 먹었어야 했어 : I should have eaten dinner
2. when verb ended as vowel + 다 as 가다(가+다) -> 가+야
집에 가야 해 : I should go home