Learn Hardcore Korean: chinguga doseogwaneseo nawayo. - A friend is coming out of the library.

The particle -가 marks 친구 as the grammatical subject of the sentence. In Korean, -가/이 is used when introducing new information or focusing on who performs the action. Here it simply tells us “the friend” is the one doing the action (coming out).

Why is the location particle -에서 used in 도서관에서 instead of -에?

-에서 indicates either (1) the place where an action happens or (2) the starting point of movement. Since 나오다 (to come out) involves movement from inside to outside, 도서관에서 denotes “from the library.” If you used 도서관에, it would only mark “to the library” or “at the library” in a static sense, which doesn’t fit with the verb 나오다.

Can -에서 mean both “at” and “from”? How do I tell which meaning to use?

Yes. With static verbs (like 있다, “to be/exist”), -에서 means “at” (e.g. 집에서 공부해요 = “I study at home”). With movement verbs (like 나오다, “to come out” or 가다, “to go”), -에서 marks the starting point (“from”), so 도서관에서 나와요 = “(Someone) comes out from the library.”

Why is the verb 나오다 conjugated as 나와요 rather than 나오아요?

When you attach -아요 to a verb whose stem ends in 오, Korean contracts 오 + 아요 into 와요. So:
• 나오 + 아요 → 나오아요 → 나와요

What’s the difference in nuance between 나와요 and 나가요?

Both verbs describe exiting, but with a subtle perspective difference:

나오다 (“to come out”) implies movement toward the speaker’s side or into an open space.
나가다 (“to go out”) implies movement away from the speaker or from an interior space to outside.

So if you’re inside watching someone leave your house, you’d use 나가요; if you’re outside and see someone emerging, you’d say 나와요.

What level of politeness is expressed by the ending -요 in 나와요?

The -요 ending here is the polite informal style (called jondaemal). It’s appropriate for most everyday conversations with strangers, acquaintances, or colleagues. It’s softer than the blunt casual style (no ending) but less formal than the highest honorific style (e.g. 나옵니다).

How would the nuance change if I used -는 instead of -가, as in 친구는 도서관에서 나와요?

Switching to -는 turns 친구 into the topic rather than a newly introduced subject. 친구는 도서관에서 나와요 would suggest you’re comparing or contrasting (e.g. “As for my friend, he/she comes out of the library [but someone else might not],” or “Whenever we talk about my friend, he/she comes out of the library”), whereas 친구가 simply states the action without that contrast.