Learn Hardcore Korean: meoriga gireoseo mukkeoya haeyo. - My hair is long, so I have to tie it up.

In Korean, 길다 (“to be long”) is an adjective that takes a subject, not an object. You use -가/이 to mark the subject of adjectives and intransitive verbs. Here 머리 (“hair” or “head”) is what’s “long,” so it becomes 머리가.

What does the connective -어서 do in 길어서?

The ending -아서/어서 links a cause or reason to its result.
• Since 길다 ends with the vowel sound “ㅡ” (not ㅏ/ㅗ), you attach -어서, giving 길어서.
• Translation nuance: “Because (my) hair is long…”

Why is it 묶어야 해요 and not 묶어요?

• 묶어요 simply states the action “(I) tie (it).”
• 묶어야 해요 uses -아/어야 하다, which expresses obligation or necessity: “must” or “have to.”
So 머리가 길어서 묶어야 해요 means “Because my hair is long, I have to tie it up.”

Can I say 묶어야 돼요 instead of 묶어야 해요?

Yes. Both -아/어야 하다 and -아/어야 되다 express necessity:
• 묶어야 해요 (more “correct” or formal)
• 묶어야 돼요 (very common in everyday speech)
The difference is subtle and both are widely used.

Could I use -고 instead of -어서 (i.e., 머리가 길고 묶어야 해요)?

You can, but the meaning changes:
• 머리가 길고 묶어야 해요 sounds like you’re simply listing facts: “My hair is long, and I have to tie it.”
• 머리가 길어서 묶어야 해요 explicitly states cause and effect: “Because my hair is long, I have to tie it.”

Why isn’t the subject “I” stated in the sentence?

Korean often omits pronouns when the subject is clear from context. Here the speaker is obviously talking about their own hair, so 저는 or 내가 isn’t needed.

Are there more casual ways to say this?

Yes. In informal speech you might hear:
• 머리 길어서 묶어야 돼.
• 머리 길어 묶어야 해.
• 머리 길어서 묶어야지.
Dropping -요 and sometimes shortening -어서 to -어/아 is very common in conversation.