Core Pattern Rule: Expressing a Decision with -기로 했다
The pattern -기로 했다 is used to express that a decision, resolution, or promise has been made to perform an action. It translates to "decided to," "resolved to," or "agreed to."
Formation
Attach -기로 하다 directly to the stem of any action verb. It doesn't matter if the stem ends in a vowel or a consonant.
가다 (to go): 가 + 기로 하다 → 가기로 하다
먹다 (to eat): 먹 + 기로 하다 → 먹기로 하다
끊다 (to quit): 끊 + 기로 하다 → 끊기로 하다
Tense
This pattern is almost always used in the past tense (-기로 했어 or -기로 했어요) because you are reporting a decision that has already been made.
나 다이어트하기로 했어. / 운동하기로 했어요. / 술 끊기로 했어.
Subject of the Decision: 'I' vs. 'We'
The meaning of -기로 했다 can shift slightly depending on whether the decision was made alone or with others. The subject of the sentence makes this clear.
Personal Decision (나/저)
When the subject is "I" (나 or 저), the pattern expresses a personal resolution or a decision made by one person.
Example: 나 담배 끊기로 했어. (I decided to quit smoking.)
Mutual Agreement (우리/저희)
When the subject is "we" (우리 or 저희), it indicates a mutual decision, agreement, or promise made between two or more people.
Example: 우리 내일 만나기로 했어. (We decided to meet tomorrow.)
Often, the subject is omitted if it's clear from the context.
공부 열심히 하기로 했어. / 우리 다시는 안 보기로 했어. / 결혼하기로 했어요. / 비밀로 하기로 했잖아.
Making Negative Decisions
To express a decision not to do something, you make the verb negative before adding -기로 했다.
Using 안 (Most Common)
The most natural and common way to form a negative decision in conversation is to place 안 directly before the verb.
Structure: 안 + Verb-기로 했다