~ 기로 했어요
‘~기로 했어요’ is used to express an appointment or a promise with someone else. It has the same meaning as ‘to promise to do (something)’. This form is usually expressed in the past tense because it describes an appointment made with someone in the past, although the plan being discussed will take place in the future.
Form ‘~기로 했어요’ is always attached directly to the end of a verb stem.
- 하다 -> 하기로 했어요
- 먹다 -> 먹기로 했어요
By Kim Min-su