Learn Hardcore Japanese: koko ha tosyokan zyanai.

You could sometimes hear ここ図書館じゃない in very casual speech, but ここは is the standard, natural way because you’re clearly setting “here” as the topic.

What is the literal, word‑for‑word breakdown of ここは図書館じゃない。?

ここ – here / this place
は – topic marker (“as for …”)
図書館 (としょかん) – library
- 図 – drawing / plan
- 書 – writing / book
- 館 – building / hall
じゃない – is not (casual negative of だ / です)

So literally:
“As for here, (it) library is-not.”
Natural English: “This is not the library.”

What exactly is じゃない? How is it different from ない?

じゃない here is the negative form of the copula だ (“to be”) in casual speech.

だ → plain “is” (informal)
じゃない → plain “is not” (informal)

This is different from ない that comes after verbs or adjectives:

行く (to go) → 行かない (don’t go)
高い (expensive) → 高くない (not expensive)

For nouns (like 図書館) and な‑adjectives, you use だ / じゃない, not bare ない:

図書館だ – it’s a library
図書館じゃない – it’s not a library

So じゃない is “is not” attached to nouns / な‑adjectives in casual style.

Is じゃない the same as ではない? Which one should I use?

じゃない is the colloquial contraction of ではない:

ではない – “is not” (neutral/formal written or careful speech)
じゃない – “is not” (casual spoken Japanese)

Relationship:

では → pronounced quickly → じゃ
ではない → じゃない

In everyday conversation with friends, じゃない is much more common.
In more formal situations or writing, you’ll see ではない or the polite ではありません.

So:

Casual: ここは図書館じゃない。
Formal / written: ここは図書館ではない。
Polite spoken: ここは図書館ではありません。

Why doesn’t the sentence end with です? Can I say ここは図書館じゃないです?

ここは図書館じゃない。 is already a complete, informal sentence.
For casual speech, nouns often just take だ / じゃない, without です.

You can say:

ここは図書館じゃないです。

This is polite-casual: it mixes casual じゃない with polite です.
It’s very common in real conversation and sounds softer than a plain じゃない。

Levels:

Very casual: ここは図書館じゃない。
Soft/polite casual: ここは図書館じゃないです。
Polite: ここは図書館ではありません。

All three mean essentially the same thing; the difference is politeness / formality.

How would I say this sentence in polite Japanese?

Two common polite versions:

ここは図書館じゃないです。 – polite-casual, common in everyday speech.
ここは図書館ではありません。 – more formally polite, used with strangers, customers, in announcements, etc.

Both are acceptable; ではありません is the safest in formal settings.

Why is there no word for “it” or “this place” in the Japanese sentence?

Japanese often omits subjects when they’re obvious from context.

In English we must say: “This is not the library.”
In Japanese, ここ already means “here / this place”, and the idea of “it is” is built into the structure:
- ここは – as for here (this place)
- 図書館じゃない – (it) is not a library

There is no separate word like “it” because the topic particle は plus context usually makes that clear. This is very common in Japanese.

What’s the difference between ここ, ここに, and ここで? Why is it just ここは here?

ここ – “here / this place” (basic form)
ここに – “here” as a location where something exists/arrives
- ここに図書館がある。– There is a library here.
ここで – “here” as a place where an action happens
- ここで勉強する。– I study here.

In ここは図書館じゃない, you are describing what “here” is, not where something exists or where an action happens, so you just use ここ + は (topic marker):

ここは – as for this place (here)
(it is) not a library

So ここは is correct because you’re identifying the place, not describing an action at the place.

Can I drop ここは and just say 図書館じゃない。?

Yes, in context, you can often drop ここは:

If you’re already standing somewhere and talking about this place, just saying 図書館じゃない。 can mean “(This place) isn’t a library.”

Japanese frequently omits topics once they’re understood. But:

With no context, 図書館じゃない。 is just “(It’s) not a library,” and what “it” is is unclear.
ここは図書館じゃない。 is clearer if you specifically need to emphasize “this place here”.

What is the nuance of using は here instead of が?

は marks the topic (“as for here”), whereas が marks the subject and often highlights contrast / focus.

ここは図書館じゃない。
- Neutral topic: “As for here, it’s not a library.” (simple statement)

ここが図書館じゃない。 can occur in a more contrasting or specific context, for example:

A: どこが図書館じゃないの？ – Which place is not the library?
B: ここが図書館じゃない。– It’s here that is not the library.

So:

Use ここは for a normal, neutral statement, which is what your sentence is.
ここが feels like you’re picking out this exact spot in contrast to something else.

Is じゃない always casual? How would I make it sound more formal or written?

Yes, じゃない is informal / spoken. To make it more formal or appropriate for writing:

ではない – neutral/formal, often in writing
- ここは図書館ではない。
ではありません – polite
- ここは図書館ではありません。

So roughly:

Casual: じゃない
Formal/written: ではない
Polite: ではありません

How do I pronounce じゃない? Is there any special stress or intonation?

Pronunciation (roughly in English sounds):

じゃ – “jah” (like ja in “Java”)
ない – “nai” (like “nai” in “nai-l” without the l)

Put together: じゃない – ja-nai

Intonation in a neutral statement like your sentence:

Usually a slight rise on じゃ and then fall over ない:
- ここは・としょかん・じゃな↓い。

In casual speech, it can be shortened or softened:

じゃない → じゃん in some dialects / casual styles, but that changes nuance (“isn’t it / right?”), so stick to じゃない for now.

Is ここは図書館じゃない。 rude? When is it okay to use this form?

It’s not inherently rude, but it is informal. Appropriateness depends on who you’re talking to:

With friends / family / classmates: perfectly fine.
With teachers, bosses, customers, strangers: too casual; use a politer form.

For more polite speech:

ここは図書館じゃないです。 – soft, polite-ish, common in conversation.
ここは図書館ではありません。 – clearly polite, safe in formal situations.

Rudeness in Japanese is mostly about politeness level and tone, not the negative meaning itself.