Learn Hardcore Indonesian: Buku sejarah itu dibaca di perpustakaan. - That history book is read in the library.

buku sejarah itu ≈ that history book / the history book (that we both know about)
So itu points to a specific book that speaker and listener can identify from context.

Why is it buku sejarah itu and not itu buku sejarah?

In Indonesian, putting itu after the noun phrase (buku sejarah itu) is the normal way to say that/the history book.

buku sejarah itu = “that history book / the history book” (neutral, common)
itu buku sejarah is possible, but usually:
- sounds more like “that is a history book” (if said as a full sentence), or
- puts more contrastive/emphatic focus on itu in speech.

So for a simple noun phrase “that history book” used as the subject, buku sejarah itu is the standard word order.

What does dibaca mean, and how is it formed?

Dibaca is the passive form of the verb baca (to read).

Root verb: baca = to read
Passive prefix: di-
di- + baca → dibaca = is read / was read / being read (depending on context)

So dibaca means “to be read” in a passive sense, with the focus on the book, not on who is doing the reading.

Is this sentence in the present or past tense? How do I know?

Indonesian verbs do not change for tense. Dibaca itself does not tell you when the action happens.

Buku sejarah itu dibaca di perpustakaan can be:

That history book *is read in the library* (present, habitual)
That history book *was read in the library* (past)

The tense must be understood from context or from added time words, for example:

Kemarin buku sejarah itu dibaca di perpustakaan.
Yesterday that history book was read in the library.
Setiap hari buku sejarah itu dibaca di perpustakaan.
Every day that history book is read in the library.

Is this an example of the passive voice? What would the active version be?

Yes. Buku sejarah itu dibaca di perpustakaan is passive.

A natural active equivalent would be:

Mereka membaca buku sejarah itu di perpustakaan.
They read that history book in the library.

Or more generally:

Orang-orang membaca buku sejarah itu di perpustakaan.
People read that history book in the library.

In the passive sentence, the focus is on buku sejarah itu (the book).
In the active sentence, the focus is on mereka/orang-orang (the readers).

Why doesn’t the sentence say who is doing the reading? Is that normal?

Yes, it’s very normal in Indonesian passive sentences to omit the agent if it’s:

obvious from context,
not important, or
general/unspecified (like “people”, “students”, “they”).

If you wanted to mention who reads it, you could add oleh:

Buku sejarah itu dibaca oleh para siswa di perpustakaan.
That history book is read by the students in the library.

But oleh + agent is often left out in everyday speech if it’s not needed.

What’s the difference between di in dibaca and di in di perpustakaan?

They are two different things that just happen to look the same:

di- in dibaca is a prefix forming the passive verb:
- di- + baca → dibaca
  It is attached to the verb with no space.
di in di perpustakaan is a preposition meaning in/at:
- di + perpustakaan = in/at the library
  It is written separately with a space.

Spelling rule to remember:

Passive prefix: di-
- verb → no space (e.g. dibaca, dimakan, ditulis)
Preposition “at/in”: di
- noun → with space (e.g. di rumah, di sekolah, di perpustakaan)

What does buku sejarah literally mean, and why is it in that order?

Literally:

buku = book
sejarah = history

In Indonesian, the main noun comes first, and its modifier (what kind of noun) comes after. So:

buku sejarah = history book (a book about history)
literally: “book [of] history”

This is the opposite of English word order, where we usually put the modifier first (history book).

Does buku sejarah itu mean one book or several books?

As written, it can most naturally be understood as one specific book, but Indonesian nouns don’t have to show plural form. Plurality is usually clear from context.

If you want to clearly show plural, you can:

buku-buku sejarah itu = those history books / the history books
semua buku sejarah itu = all those history books

Without any plural marking, buku sejarah itu is most commonly interpreted as a single, specific history book.

Could I say sebuah buku sejarah here? What’s the difference?

Yes, you could say:

Sebuah buku sejarah dibaca di perpustakaan.

Sebuah is a classifier that often translates as “a” / “one (piece of)” for objects like books.

Differences:

buku sejarah itu = that history book / the history book (specific, known)
sebuah buku sejarah = a history book (non-specific, just one such book)

So adding sebuah makes it clear you mean one, non-specific history book, while itu makes it definite and specific.

What is the function of di perpustakaan exactly? Is di always “in/at”?

Di perpustakaan is a prepositional phrase showing location:

di = in / at / on (location marker)
perpustakaan = library

So di perpustakaan = in the library / at the library.

Di is used for static location (“where something is happening”), not motion. For motion towards a place, you would usually use ke:

Saya pergi ke perpustakaan. = I go to the library.
Saya belajar di perpustakaan. = I study in/at the library.

Can I add sedang in this sentence? What would Buku sejarah itu sedang dibaca di perpustakaan mean?

Yes, that’s a very natural sentence.

sedang marks an ongoing action, similar to English “is … -ing”.
Buku sejarah itu sedang dibaca di perpustakaan.
≈ That history book is being read in the library (right now).

Without sedang, dibaca can mean:

generally / habitually read, or
read at some time (past or present), depending on context.

With sedang, the sentence clearly focuses on an action currently in progress.