Learn Hardcore Indonesian: Saya membaca buku pertanian di perpustakaan. - I read an agriculture book in the library.

Saya = more formal, polite, neutral; safe in almost any situation (with strangers, in class, at work, writing, etc.).
Aku = more informal, used with friends, family, people close to you, in songs, on social media.

In Saya membaca buku pertanian di perpustakaan., saya is chosen because it’s neutral and standard.

You can say Aku membaca buku pertanian di perpustakaan., but that sounds more casual and depends on your relationship with the listener.

Do I always have to say saya? Can I drop the subject?

You can drop saya if the context already makes it clear who is acting.

Full: Saya membaca buku pertanian di perpustakaan.
Dropped subject: Membaca buku pertanian di perpustakaan.

The second one sounds like (I’m) reading an agriculture book in the library when the subject is understood from context. This is very common in Indonesian.

However, when you’re learning or when the subject might be unclear, keeping saya is a good idea.

Why is there no word for the or a/an in this sentence?

Indonesian doesn’t have articles like the or a/an.

Buku pertanian can mean:

an agriculture book
the agriculture book
agriculture books (in some contexts)

Whether it’s a or the depends entirely on context, not on a specific word.

If you need to be very explicit:

sebuah buku pertanian = one agriculture book (often translated as a(n), but literally one)
buku pertanian itu = that/that particular agriculture book (often feels like the in context)

Why is membaca used instead of baca?

The base verb is baca (to read).
Membaca is the standard active verb form created with the prefix meN-:

baca → membaca

General pattern:
meN- + root verb = neutral active verb form (like to read / reading / read in sentences).

Use membaca in normal sentences with a subject:

Saya membaca buku. = I read / am reading a book.

Baca without meN- appears in:

Imperatives: Baca buku ini! = Read this book!
Informal speech, headlines, notes: Saya lagi baca buku. = I’m reading a book.

So here, membaca is the standard, “textbook” form.

How can membaca mean both read and am reading? Where is the tense?

Indonesian verbs do not change for tense. Membaca itself is tenseless.

Saya membaca buku pertanian di perpustakaan. can mean:

I read an agriculture book in the library. (past)
I am reading an agriculture book in the library. (present)
I will read an agriculture book in the library. (future – less common, but possible with context)

To show time more clearly, Indonesian uses time words:

tadi / tadi pagi = earlier / earlier this morning
- Tadi saya membaca buku… = Earlier I read a book…
sekarang = now
- Sekarang saya membaca buku… = Now I am reading a book…
nanti / besok = later / tomorrow
- Besok saya akan membaca buku… = Tomorrow I will read a book…

Without those, the tense relies on context.

What exactly does buku pertanian mean? Is it agricultural book, book of agriculture, or book about agriculture?

Buku pertanian literally is agriculture book, but the most natural English is a book about agriculture or an agriculture book.

Structure:

buku = book
pertanian = agriculture / farming (a noun)

In Indonesian, the modifier usually comes after the noun:

buku pertanian = agriculture book / book about agriculture
buku sejarah = history book
buku matematika = math book

So buku pertanian means a book whose topic is agriculture.

Can I say pertanian buku instead of buku pertanian?

No. That word order is wrong in Indonesian.

Correct pattern is:

noun + modifier

So:

buku pertanian (correct)
pertanian buku (incorrect)

Other examples:

rumah sakit (sick house → hospital), not sakit rumah
mobil merah (red car), not merah mobil

What does di perpustakaan mean exactly? Is di more like in or at?

Di is a general preposition for location and can often be translated as in, at, or sometimes on depending on context.

di perpustakaan
- di = at / in
- perpustakaan = library

So di perpustakaan can be:

in the library
at the library

Both are fine in English. Indonesian doesn’t distinguish as strictly as English here.

What is the structure of perpustakaan? It looks long. Is it related to pustaka?

Yes. Perpustakaan is built from the root pustaka.

pustaka = book, writing, literature (less common in everyday speech)
per- … -an = a common noun-forming circumfix that often means place for / related to

So:

per + pustaka + an → perpustakaan = place of books → library

This per- … -an pattern shows up in many place nouns:

perkantoran (kantor = office) → office complex / offices area
perumahan (rumah = house) → housing complex

Could di perpustakaan be moved in the sentence, or must it be at the end?

You can move di perpustakaan as long as the meaning stays clear:

Saya membaca buku pertanian di perpustakaan. (most natural / neutral)
Di perpustakaan saya membaca buku pertanian. (emphasis on at the library)
Saya di perpustakaan membaca buku pertanian. (also possible, with slight emphasis that you are at the library when doing the reading)

The most common everyday order is still: [Subject] [Verb] [Object] [Place]
→ Saya membaca buku pertanian di perpustakaan.

How do I make buku pertanian plural, like agriculture books?

Indonesian often leaves plurals unmarked. Buku pertanian can already mean agriculture books if the context suggests more than one.

If you want to make it clearly plural, you can:

Reduplicate: buku-buku pertanian = agriculture books (more than one)
Add a quantity: tiga buku pertanian = three agriculture books
Use banyak: banyak buku pertanian = many agriculture books

Example:

Saya membaca banyak buku pertanian di perpustakaan.
= I read many agriculture books in the library.

Is the word order always Subject–Verb–Object–Place in Indonesian?

The most neutral, common order is:

Subject – Verb – Object – (Adverbials like place/time)

So:

Saya (Subject)
membaca (Verb)
buku pertanian (Object)
di perpustakaan (Place)

This order is very typical and usually the safest choice.

You can move things around for emphasis or style, especially adverbials (place, time), but the basic SVO backbone is very common and a good default as you learn.

If I want to add a time word like yesterday or now, where should it go?

Time words are flexible, but common positions are:

At the beginning (very common):
- Kemarin saya membaca buku pertanian di perpustakaan.
  = Yesterday I read an agriculture book in the library.
After the subject:
- Saya kemarin membaca buku pertanian di perpustakaan.
At the end (less common for kemarin, but possible):
- Saya membaca buku pertanian di perpustakaan kemarin.

All are grammatical; the difference is mostly nuance/emphasis. For beginners, putting time words at the beginning or right after the subject is a good habit.