Learn Hardcore Korean: naeireun kkok hakgyoe gaya haeyo.

The particle -은 marks 내일 (“tomorrow”) as the topic, signaling “as for tomorrow…”. If you used 내일이, you’d simply be stating “tomorrow” as the grammatical subject. Using -은/는 often adds a contrastive or topical nuance, like “speaking of tomorrow…”.

What does 꼭 add to the sentence?

꼭 means “definitely,” “without fail,” or “for sure.” It emphasizes that going to school is non‐negotiable: 내일은 꼭 학교에 가야 해요 = “Tomorrow I absolutely must go to school.”

Why is the particle 에 used in 학교에 가야 해요?

The particle 에 marks the destination or direction of movement. When you go somewhere, you attach 에 to the place name. Thus 학교에 means “to school.”

How does 가야 해요 express obligation?

가야 해요 comes from the structure -아/어야 하다, which expresses necessity or obligation. Here’s the breakdown:
1) 가다 (“to go”) → stem 가-
2) Add -아야 → 가야 (“must go”)
3) Attach 하다 and make it polite → 가야 해요 (“have to go”)

Can you break down the formation of 가야 해요 step by step?

Start with 가다 (to go).
Drop -다, leaving 가-.
Add -아야 (from -아/어야 하다): 가
- 야 = 가야 (“must go”).
Add 하다 as the main verb: 가야 하다.
Conjugate 하다 politely: 가야 해요.

Is there a difference between 가야 해요 and 가야 돼요?

No significant difference in meaning—they both mean “must go.”

가야 해요 comes from -아야 하다.
가야 돼요 comes from -아야 되다.
Both are common; -돼요 can sound a bit more colloquial, but they’re interchangeable.

Could you use 내일은 꼭 학교에 가야 돼요 instead, and would it be correct?

Yes. 내일은 꼭 학교에 가야 돼요 is perfectly correct. It simply uses -아야 되다 for obligation. The overall meaning is still “I absolutely must go to school tomorrow.”

How would you say this sentence in a more casual (informal) style?

You can drop the polite endings:

내일은 꼭 학교에 가야 해.
내일은 꼭 학교에 가야 돼.
Even shorter:
내일 꼭 학교 가야 돼.