Learn Hardcore Korean: doseogwaneseoneun dambaereul piul su eobseoyo. - You can’t smoke cigarettes in the library.

에 marks a static location/existence (be at/in). Example: 도서관에 있어요 = “I’m at the library.”
에서 marks the place where an action happens. Smoking is an action, so 도서관에서 is needed.
Adding the topic marker to get 도서관에서는 makes that location the topic/contrast: “As for the library, (you can’t smoke).” Without 는, it’s neutral. With 는, it subtly implies contrast with other places.
The contracted form 도서관에선 is also fine in speech and informal writing.

What’s going on with 피울 수 없어요? Why 피울 and not 피워?

-(으)ㄹ 수 없다/있다 attaches to the verb stem in its “attributive future” form before the noun 수.
Examples:
- 하다 → 할 수 없다 (cannot do)
- 보다 → 볼 수 없다 (cannot see)
- 먹다 → 먹을 수 없다 (cannot eat)
- 피우다 → 피울 수 없다 (cannot smoke)
So it must be 피울 수 없어요, not 피워 수 없어요.

What does 수 없다 literally mean?

수 is a native noun meaning “way/method/possibility,” so 수 없다 literally means “there is no way/possibility.”
In context it conveys “cannot,” often implying lack of permission or possibility. Here it reads as a rule: “You’re not allowed to smoke.”

How is 피울 수 없어요 different from 못 피워요 and 피우면 안 돼요?

피울 수 없어요: “cannot” in terms of possibility/permission; sounds slightly objective or rule-like.
못 피워요: “can’t smoke” (often inability or external circumstances). It can also imply not allowed, but is a bit more casual/ambiguous.
피우면 안 돼요: “must not smoke” (clear prohibition). Strongest for rules: 도서관에서는 담배를 피우면 안 돼요.

Why is it 담배를? Do I have to use the object marker 를?

담배를 피우다 treats “cigarette” as the object of the verb “smoke,” so 를 is the standard object marker.
In speech, Koreans often drop object markers: 담배 피울 수 없어요 is common and natural.
Keep 를 in careful writing or when you want clarity.

Can I say 담배는 instead of 담배를?

담배는 makes “cigarettes” the topic/contrast: 도서관에서는 담배는 피울 수 없어요 = “As for cigarettes (at the library), you can’t smoke them,” implying a contrast (e.g., other things/activities might be okay).
Without a clear contrast, using 는 here can sound oddly contrastive. 담배를 is the neutral choice.

Is it 담배를 피우다 or 담배를 피다? And what about 펴요?

The standard textbook form is 담배를 피우다.
In everyday speech, many say 담배(를) 피다/펴요 as a colloquial shortening. It’s common in conversation, but stick with 피우다 (피워요) in writing or formal settings.

Can I shuffle the word order?

Yes. Korean allows some flexibility:

도서관에서는 담배를 피울 수 없어요 (neutral, common)
담배를 도서관에서는 피울 수 없어요 (emphasizes the place as the restriction)
도서관에서(는) 담배는 피울 수 없어요 (emphasizes the item being restricted) The verb typically comes last.

What level of politeness is 없어요? What are other forms?

Why is there a space in 피울 수 없어요?

Any pronunciation tips for this sentence?

없어요 is pronounced close to “업써요.”
피울 keeps both vowels; say it as two syllables “피-울,” with a brief w-glide feeling.
도서관에서는 links smoothly across word boundaries; just keep a natural flow without pausing between particles.
In fast speech, 담배를 may sound like “담배를/담배를(ㄹ weakened)” and 에서는 like “에선.”

If I mean “inside the library,” should I add 안?

도서관에서는 already implies “at/in the library” for actions.
도서관 안에서는 explicitly says “inside the library,” adding emphasis that the interior space is meant (useful if contrasting with outside: 밖에서는).

What does 도서관에서는 담배를 피울 수가 없어요 mean?

Adding -가 to 수 (→ 수가) adds emphasis: “There’s just no way to smoke in the library.”
It strengthens the impossibility/ban.

How would this be phrased on signs or in very formal language?