Learn Hardcore Japanese: tosyokan ni ha takusan hon ga arimasu.

図書館に本があります。
= There are books in the library. (simple statement of fact)
図書館には本があります。
= As for the library, (there) are books.
This slightly emphasizes the library as the topic. It can imply contrast, like:
- At home there aren’t many books, but in the library there are (many).

So には here means something like “as for in the library…”.

What’s the difference between 図書館にたくさん本があります and 図書館にはたくさん本があります?

Grammatically, both are correct and mean that there are many books in the library. The difference is nuance:

図書館にたくさん本があります。
Neutral description. Just stating a fact: in the library, there are many books.
図書館にはたくさん本があります。
The は makes 図書館に the topic, which can:
- Highlight the library in contrast to other places, or
- Sound a bit more “as for the library…”, a bit more explanatory.

If you just want to say it straightforwardly, 図書館にたくさん本があります is safe.
If you are contrasting (e.g., 家にはあまり本がありませんが、図書館にはたくさん本があります), then には feels more natural.

Why is 本 marked with が and not は?

In 本があります, the が marks 本 as the thing that exists / appears. In existence sentences (there is/are), が is the default particle:

本があります。 = There is a book / There are books.
猫がいます。 = There is a cat.

If you use 本は, you are making 本 the topic instead:

本は図書館にあります。
= As for the book(s), (they) are in the library.

So:

本があります → introducing the existence of books.
本はあります → talking about books that are already known or topical, then saying where or whether they exist.

In the sentence you gave, we’re introducing the existence of many books, so 本が is natural.

Why do we use あります instead of です in this sentence?

あります is the verb “to exist, to be (there), to have” for inanimate things (non-living, or at least non-moving in context: books, chairs, buildings, etc.).

です is a copula that links two things, like A is B:

これは本です。 = This is a book.
図書館は静かです。 = The library is quiet.

But in 本があります, we’re not saying “books are something”; we are saying “books exist / there are books” in a location. That is exactly what あります does.

So:

図書館に本があります。 = There are books in the library.
You cannot replace あります with です here.

What’s the difference between あります and います?

Both mean “to exist / there is / there are”, but:

あります is used for inanimate things:
- objects, places, plants, abstract things
- 本があります。 = There is a book.
- 木があります。 = There is a tree.
います is used for animate beings:
- people, animals, sometimes robots if treated as animate
- 人がいます。 = There is a person.
- 犬がいます。 = There is a dog.

So 本 is inanimate, so we use あります, not います.

Is たくさん an adjective or an adverb? Where can it go in the sentence?

たくさん is a quantity word (often treated as an adverb), and it can modify verbs and nouns in a few patterns.

Common patterns:

たくさん本があります。
- たくさん comes before the noun+verb chunk.
- Very natural: There are many books.
本がたくさんあります。
- たくさん comes right before the verb, modifying あります.
- Also natural: There are many books.
たくさんの本があります。
- Here たくさんの works more like an adjective phrase: many books.
- Slightly more formal / explicit.

In daily conversation, たくさん本があります and 本がたくさんあります are very common. All three patterns are acceptable.

What’s the difference between たくさん本があります and たくさんの本があります?

Both can be translated as “there are many books”, but:

たくさん本があります。
- A bit more colloquial and light.
- Feels like “there are lots of books”.
たくさんの本があります。
- Grammatically more like “there are many books” with たくさんの directly modifying 本.
- Slightly more formal or written, or just more explicitly “many books” as a noun phrase.

In everyday spoken Japanese, you’ll probably hear たくさん本があります or 本がたくさんあります more often than たくさんの本があります, but all are correct.

Could we say 本がたくさんあります instead of たくさん本があります? Is there any nuance difference?

Yes, 本がたくさんあります is perfectly natural and very common.

Nuance:

たくさん本があります。
- Slightly more focus on the quantity word first: “(There are) many books.”
- Very normal in speech.
本がたくさんあります。
- The pattern Xがたくさんあります sounds very natural as a unit:
  - 人がたくさんいます。 (There are many people.)
  - 店がたくさんあります。 (There are many shops.)

In practice, both sound natural; any difference is very subtle. You can freely use either.

Why do we use 図書館に and not 図書館で here?

に and で both can follow place words but have different roles:

に = location where something exists / ends up / arrives
- 図書館に本があります。 = Books exist in the library.
- 机の上にペンがあります。 = There is a pen on the desk.
で = location where an action happens
- 図書館で本を読みます。 = I read books at the library.
- 公園で遊びます。 = (We) play in the park.

In 本があります, the verb is existence, not an action like reading or playing, so you need に, not で.

What is the literal word-by-word structure of 図書館にはたくさん本があります in English?

Breaking it down:

図書館に = in the library (location marker)
は = topic marker (as for ~, speaking of ~)
たくさん = many / a lot of
本 = book(s)
が = subject marker (for what exists)
あります = there is / there are (for inanimate things)

Putting it into a literal topic–comment structure:

図書館には = As for in the library,
たくさん本が = many books
あります = exist / there are.

So a literal-ish English reading would be:
“As for in the library, there are many books.”
Natural English: “There are many books in the library.”

How would I say this sentence in casual speech, or in negative / past forms?

Base polite sentence:

図書館にはたくさん本があります。
= There are many books in the library. (polite)

Casual form (present):

図書館にはたくさん本がある。
- Just change あります → ある.

Negative (polite):

図書館にはたくさん本がありません。
= There are not many books in the library.

Negative (casual):

図書館にはたくさん本がない。

Past (polite):

図書館にはたくさん本がありました。
= There were many books in the library.

Past (casual):

図書館にはたくさん本があった。