Learn Hardcore Indonesian: Saya menulis kosakata baru di buku harian.

Past: Tadi saya menulis kosakata baru di buku harian. (Earlier I wrote…)
Present continuous: Saya sedang menulis kosakata baru di buku harian. (I am currently writing…)
Future: Saya akan menulis kosakata baru di buku harian. (I will write…)

Why is it menulis and not just tulis?

Tulis is the base verb (write), and menulis is the standard active form made with the prefix meN-:

tulis → menulis

Usage differences:

menulis is used in normal statements:
- Saya menulis kosakata baru. – I write new vocabulary.
tulis (without meN-) often appears in:
- Imperatives: Tulis kosakata baru di buku harian! – Write the new vocabulary in your diary!
- Compounds or set phrases: alat tulis (stationery), tulisan (writing, text).

So in a normal sentence with saya as the subject, menulis is the natural choice.

What exactly does kosakata mean? Is it singular or plural?

Kosakata means “vocabulary” (literally something like word-treasury).

It behaves more like an uncountable noun in English (“vocabulary”), not like a word or words:

kosakata = vocabulary in general, or a set of vocabulary items
It doesn’t change form for plural. Context tells you if it’s “vocabulary” in general or “vocabulary items / words”.

In kosakata baru, you can understand it as:

new vocabulary
or more concretely new vocabulary items / new words

If you really want to stress “words”, you can say:

kata-kata baru – new words (literally “words-words new”)

What is the difference between kosakata baru and kata-kata baru?

Both can be used, but there’s a nuance:

kosakata baru
- Focuses on vocabulary as a set.
- Very common in learning contexts: Belajar kosakata baru (to learn new vocabulary).
kata-kata baru
- Focuses more on individual words.
- You might use it when talking about specific words you encountered:
  - Saya belajar beberapa kata-kata baru hari ini. – I learned some new words today.

In your sentence, Saya menulis kosakata baru di buku harian, kosakata baru is very natural for a learner recording vocabulary.

Why is the word order kosakata baru, not baru kosakata?

In Indonesian, most adjectives come after the noun they describe. So:

kosakata baru = new vocabulary
buku harian = daily book → diary
rumah besar = big house

Putting baru before the noun (baru kosakata) is not normal Indonesian for this meaning and would sound wrong in this context.

So the pattern is generally:
> noun + adjective
> kosakata + baru → kosakata baru

What does buku harian literally mean, and does it always mean “diary”?

Literally:

buku = book
harian = daily (from hari “day”)

So buku harian is a “daily book”, which in practice means a diary or journal.

Usage:

In everyday Indonesian, buku harian is the standard term for diary.
harian by itself can also mean “daily (newspaper)” in combinations like:
- koran harian = daily newspaper
- surat kabar harian = daily newspaper

But in buku harian, the fixed phrase is understood as diary.

How do I say explicitly “in my diary”? Is di buku harian enough?

Di buku harian only means “in the diary / in a diary”; it doesn’t show whose diary it is.

To say “in my diary”, you normally add saya after the noun phrase:

di buku harian saya – in my diary

So:

Saya menulis kosakata baru di buku harian saya.
= I write new vocabulary in my diary.

Indonesian usually puts the possessive pronoun after the noun:

buku saya – my book
rumah mereka – their house
buku harian saya – my diary

Can I drop saya and just say Menulis kosakata baru di buku harian?

Yes, you can drop saya in many contexts because Indonesian allows omitting the subject when it’s clear from context.

So:

Menulis kosakata baru di buku harian.

could work as:

A diary note heading
A bullet point on a to-do list
A sentence where the subject is already obvious from previous context

However, as a neutral, standalone sentence (for a learner exercise or textbook example), including Saya is clearer and more natural:

Saya menulis kosakata baru di buku harian.

Is the word order flexible? Could I say Saya di buku harian menulis kosakata baru?

Basic, most natural order is:

Subject – Verb – Object – Location
Saya – menulis – kosakata baru – di buku harian

So:

Saya menulis kosakata baru di buku harian. ✅ natural

Saya di buku harian menulis kosakata baru is grammatically possible but sounds awkward and unnatural in everyday Indonesian. Normally you don’t put the location between the subject and the main verb unless there’s a special emphasis or different structure.

Stick with:

Saya menulis kosakata baru di buku harian.

Could I use mencatat instead of menulis here? What’s the difference?

Yes, you could say:

Saya mencatat kosakata baru di buku harian.

Nuance:

menulis = to write (general writing)
mencatat = to note down / record, often for the purpose of remembering or keeping a record

For vocabulary learning:

menulis kosakata baru – I write new vocabulary (neutral)
mencatat kosakata baru – I make a note of / record new vocabulary (slightly more “study/record” focused)

Both are acceptable. Menulis is more general; mencatat feels more like taking notes.

Why is the preposition di used here, and how is it different from pada?

Di is the normal preposition for location: “in, at, on”.

di buku harian = in the diary / in my diary

Pada is more formal and is often used:

With abstract “locations” (time, situations, people):
- pada hari Senin – on Monday
- pada kesempatan ini – on this occasion
- pada mereka – to them
In formal or written language, e.g. official letters and documents

In this sentence, because buku harian is a physical object, di is the normal, natural choice:

Saya menulis kosakata baru di buku harian. ✅
Saya menulis kosakata baru pada buku harian. sounds stiff/unnatural in everyday speech.

Is di always written separately here, or can it be joined like dibuku?

Here, di is a preposition (meaning “in/at/on”), so it must be written separately:

di buku harian ✅ correct
dibuku harian ❌ incorrect

Important distinction:

di + noun (location) → always separate
- di rumah, di sekolah, di buku harian
di- + verb (passive prefix) → attached to the verb
- ditulis – is/was written
- dibaca – is/was read

Your sentence uses di as a preposition, so it’s always two words: di buku.

Do I need a word like “some” here, e.g. “some new vocabulary”?

No, you don’t have to add anything. Indonesian often leaves quantity implicit if it’s not important.

Saya menulis kosakata baru di buku harian.
→ I write (some) new vocabulary in my diary.

If you want to be explicit, you can add a quantifier:

Saya menulis beberapa kosakata baru di buku harian.
– I write some new vocabulary items in my diary.
Saya menulis banyak kosakata baru di buku harian.
– I write a lot of new vocabulary in my diary.

But the basic sentence without a quantifier is perfectly natural.

Could I use aku instead of saya here? What’s the difference in tone?

Yes, grammatically you can say either:

Saya menulis kosakata baru di buku harian.
Aku menulis kosakata baru di buku harian.

Difference:

saya
- More formal / polite / neutral
- Used with strangers, in formal settings, in writing, etc.
aku
- More informal / intimate
- Used with close friends, family, in songs, or in a personal diary

For a diary entry, Aku menulis kosakata baru di buku harian would sound very natural, because you’re talking to yourself. For a textbook or classroom sentence, Saya is the safe default.