Core Pattern Rule: Expressing a Guess with -(으)ㄹ걸
The pattern -(으)ㄹ걸 is used to express the speaker's guess, assumption, or supposition about a situation. It's similar to saying "I bet...", "Probably...", or "I'm guessing that..." in English. It's typically used in casual conversation and implies that the speaker isn't 100% certain.
Formation Rules
This ending attaches directly to verb and adjective stems.
Vowel or ㄹ ending stems: Add -ㄹ걸
가다 (to go) → 갈걸
만들다 (to make) → 만들걸
Consonant ending stems (except ㄹ): Add -을걸
먹다 (to eat) → 먹을걸
많다 (to be many) → 많을걸
Past Tense: Add -았/었을걸 to the stem.
닫다 (to close) → 닫았을걸
팔리다 (to be sold) → 팔렸을걸
Nouns: Add -일걸.
사실이 아니다 (to not be true) → 사실이 아닐걸
아마 문 닫았을걸? / 지금 가면 늦을걸? / 그거 매울걸? / 사실이 아닐걸?
Native Nuance: A Soft Contradiction or Warning
Beyond a simple guess, -(으)ㄹ걸 carries a specific nuance of gently contradicting someone or offering a mild warning. It's a softer, less confrontational way to present a different perspective.
Softening an Opinion
Instead of stating a fact directly (e.g., "It's boring"), using -(으)ㄹ걸 softens your opinion. It implies, "That's what I think, but you might feel differently."
재미없을걸? (I bet it's boring.) - This sounds less blunt than 재미없어.
Mild Warning or Dissuasion
The pattern is often used to suggest that an action might have a negative consequence, without being overly direct.
지금 가면 늦을걸? (You'll probably be late if you go now.) - This implies, "...so maybe you shouldn't go."
그거 지금 사면 비쌀걸? (It'll probably be expensive if you buy it now.) - This suggests, "...so maybe you should wait."
Important: Do not confuse this with -(으)ㄹ 걸 그랬다, which means "I should have..." and expresses regret about something you didn't do in the past.
재미없을걸요? / 그거 지금 사면 비쌀걸요? / 힘들걸? / 벌써 다 팔렸을걸요?
Politeness & Formality
This pattern has two common forms that signal different levels of politeness. The choice depends on your relationship with the listener.
Casual Form: -(으)ㄹ걸
This is the base form (반말) and is used when speaking to close friends, family members, or people who are younger than you. It has a friendly, informal feel.
Example: 걔는 안 올걸? (I bet he won't come.)
Polite Form: -(으)ㄹ걸요
By simply adding 요 to the end, you create the standard polite form (해요체). Use -(으)ㄹ걸요 when speaking to people you don't know well, colleagues, or anyone older than you. The meaning of making a guess remains exactly the same; only the level of respect changes.
Example: 그 친구는 안 올걸요? (I bet he won't come.)
후회할걸? / 후회할걸요? / 사람 많을걸? / 사람 많을걸요? / 호리는 집에 있을걸? / 호리 씨는 집에 있을걸요?