Learn Hardcore Indonesian: Botol plastik itu kosong sekarang.

Botol plastik itu can be understood as that plastic bottle (pointing/known from context).
In many real situations, it just means the plastic bottle (we both know which one).

So itu marks that the speaker assumes the listener knows which bottle is being talked about, either because it was mentioned before or is visible/obvious.

Why is there no word for is in Botol plastik itu kosong sekarang?

Indonesian usually drops a separate “to be” verb (like is/are) when describing a noun with an adjective:

Botol plastik itu kosong. → The/That plastic bottle is empty.
Dia tinggi. → He/She is tall.
Makanan ini enak. → This food is tasty.

You can insert adalah in very formal or written language, but it sounds stiff in this simple sentence:

Botol plastik itu adalah kosong sekarang. → grammatically possible, but unnatural in normal conversation.
Use the shorter version.

Why does itu come after botol plastik, not before it like that plastic bottle in English?

In Indonesian, demonstratives ini (this) and itu (that) almost always come after the noun phrase:

buku ini → this book
buku itu → that book / the book
botol plastik itu → that/the plastic bottle

So the normal structure is:

[Noun + modifiers] + ini/itu

Putting itu before the noun (itu botol plastik) is possible, but it changes the feel: it becomes more like that bottle (of plastic) as a topic, or a more emphatic that bottle, depending on context. The standard neutral form here is botol plastik itu.

What exactly does botol plastik mean? Is it plastic bottle or bottle of plastic?

Botol plastik means plastic bottle (a bottle made of plastic).

Head noun: botol (bottle)
Modifying noun: plastik (plastic)

Noun + noun like this often forms a compound where the second noun describes the material, type, or category:

tas kulit → leather bag
gelas kaca → glass cup
botol plastik → plastic bottle

If you really want to say bottle of plastic (material) in a literal sense, you would usually use dari:

botol dari plastik → a bottle made from plastic

But in everyday use, botol plastik is exactly plastic bottle.

What does kosong mean, and can it be used in other contexts?

In this sentence, kosong means empty (no contents inside the bottle).

Common uses:

gelas itu kosong → that glass is empty
perut saya kosong → my stomach is empty
ruangan itu kosong → that room is empty
lembaran ini masih kosong → this sheet is still blank/empty

It can also be used metaphorically, similar to English:

kata-katanya kosong → his/her words are empty (no substance)
hidup yang kosong → an empty life

So kosong is a general word for empty / blank / void, depending on context.

Why is sekarang at the end? Could it go somewhere else?

Sekarang means now. Time words like sekarang, kemarin (yesterday), besok (tomorrow) are flexible in position. All of these are possible:

Sekarang botol plastik itu kosong.
Botol plastik itu sekarang kosong.
Botol plastik itu kosong sekarang.

All are grammatical. The meaning is basically the same. The most neutral and common in casual speech is usually:

Botol plastik itu kosong sekarang.

Putting sekarang first can add a slight emphasis on the time: Now, that plastic bottle is empty.

Can I drop itu and just say Botol plastik kosong sekarang?

You can, but it changes the nuance.

Botol plastik itu kosong sekarang.
→ That/the plastic bottle (a specific one we both know) is empty now.
Botol plastik kosong sekarang.
→ Sounds more general or indefinite, like plastic bottles are empty now/a plastic bottle is empty now, depending on context. It doesn’t clearly point to one specific, known bottle.

Without itu (or ini), Indonesian often sounds more generic or indefinite, similar to a / some in English.

How would I say The plastic bottles are empty now (plural)?

Indonesian usually does not change the form of the noun for plural. Context shows whether it’s singular or plural.

So:

Botol plastik itu kosong sekarang.
can mean:
- The plastic bottle is empty now, or
- The plastic bottles are empty now,

depending on context (and sometimes tone or gestures).

If you really want to emphasize plurality, you have some options:

Botol-botol plastik itu kosong sekarang.
(reduplication for plural: those plastic bottles are empty now.)
Semua botol plastik itu kosong sekarang.
(all those plastic bottles are empty now.)

In everyday conversation, just botol plastik itu kosong sekarang will often be enough; context does the rest.

Could I say Botol plastik itu sudah kosong sekarang? What does sudah add?

Yes, that’s natural. Sudah means already (or indicates that a change has happened).

Botol plastik itu kosong sekarang.
→ The bottle is empty now (simple fact).
Botol plastik itu sudah kosong sekarang.
→ The bottle is already empty now (suggests it used to have something, and you’re highlighting the change or completion).

Use sudah when you want to emphasize “it has become empty / it’s already empty by now”.

Is there any situation where I need a classifier like sebuah in this sentence?

You can add a classifier, but you don’t have to.

Sebuah botol plastik itu kosong sekarang. → unnatural; you generally don’t put sebuah before a noun that already has itu/ini.
Sebuah botol plastik kosong sekarang. → A plastic bottle is empty now (no itu, more like reporting the existence).

Typical uses:

sebuah botol plastik → a/one plastic bottle (counting, introducing)
botol plastik itu → that/the plastic bottle (specific, known)

In this sentence, because you are already pointing to a specific known bottle with itu, you don’t need sebuah.

How do you pronounce kosong and botol? Especially the ng in kosong.

Approximate pronunciation (in simple English-like spelling):

botol → BOH-tol
- bo as in bottle (first syllable)
- tol like toll but with a clear t and short o
kosong → KOH-song
- ko like co in coffee (without the ffee)
- song like English song

The ng in kosong is the same sound as in English sing, long, song: a single nasal sound at the back of the mouth, not n + g separately.

Does Botol plastik itu kosong sekarang imply anything about the past, like “it used to be full”?

By itself, Botol plastik itu kosong sekarang just states the current condition: the bottle is empty now. It does not automatically imply what it was like before.

If you want to clearly imply a change, you normally add sudah or use context:

Botol plastik itu sudah kosong sekarang.
→ It’s (already) empty now (implies change).

Often, though, real-life context carries that meaning even without sudah. For example, if you just watched someone drink from it, kosong sekarang will naturally be understood as it used to have something, now it’s empty.

Can itu also work like that one referring back to something already mentioned, not just as a pure determiner?

Yes. Itu is very flexible. In botol plastik itu, it functions as a demonstrative determiner (that/the). But itu can also refer back to something like that one / that thing / that situation.

For example, in a longer dialogue:

A: Saya suka botol kaca. (I like glass bottles.)
B: Botol plastik itu kosong sekarang.
→ That plastic bottle is empty now. (referring to a specific one in the shared situation)

Or:

A: Mana botol yang kamu pakai tadi? (Where is the bottle you used earlier?)
B: Botol plastik itu kosong sekarang.
→ Here itu ties the noun phrase to something already discussed (“that one we were just talking about”).

So itu often signals “the specific one we’re both thinking about now”.