Learn Hardcore Indonesian: Pembelian hari ini dicatat di buku kecil. - Today’s purchases are recorded in the small notebook.

Yes. The verb dicatat uses the passive prefix di-. The subject is Pembelian hari ini (“today’s purchases”), and the doer is not mentioned. This focuses on the result (they are recorded) rather than who records them. To name the agent, add oleh: Pembelian hari ini dicatat oleh kasir.

How would I say it in the active voice?

Kasir mencatat pembelian hari ini di buku kecil. (The cashier records…)
With the object fronted (very common): Pembelian hari ini saya catat di buku kecil. This is the “short passive” (pasif 2) pattern with a pronoun agent.

What’s the difference between di- in dicatat and di in di buku kecil?

di- (attached, no space) = passive verb prefix: di
- catat → dicatat.
di (separate) = preposition “in/at/on”: di buku kecil = “in a small notebook.” The spacing changes the meaning.

What exactly does pembelian mean, and how is it formed?

From the verb beli (“to buy”):

peN- + beli + -an → pembelian = “purchase; the act of buying.” Contrast:
pembeli = “buyer (person).”
belanja/pembelanjaan = “shopping; expenditure (budgetary),” not the same as pembelian.

Is pembelian singular or plural here?

Indonesian doesn’t mark number by default. pembelian can mean “purchase” or “purchases.” To be explicit:

Plural emphasis: pembelian-pembelian or semua pembelian.
Singular/one item: satu/sebuah pembelian (rare) or rephrase with the actual item (e.g., satu pembelian tiket).

Does hari ini modify the noun “purchases” or the time of recording?

As written, it most naturally means “today’s purchases” (noun + time modifier). If you mean the action happened today, make it clear:

Pembelian itu dicatat hari ini.
Or front the time: Hari ini, pembelian dicatat di buku kecil.

Why is it di buku kecil and not ke/pada something?

di marks the place where the writing exists: “in/on the notebook.” That’s the normal choice for recording/writing.
ke means movement “to(ward)” and isn’t used for where text resides.
pada can mean “on/at” in formal style, but with writing surfaces Indonesians still prefer di. You may see pada halaman 5 in formal texts; di halaman 5 is also common.
To stress “inside,” di dalam buku kecil is acceptable but usually unnecessary.

How do I say “in the small notebook” versus “in a small notebook”?

“the small notebook”: di buku kecil itu (or di buku kecil ini = “this”).
“a small notebook”: di sebuah buku kecil. The classifier sebuah adds “one/a,” but it’s often omitted if context is clear.

Why is it buku kecil, not kecil buku?

Adjectives normally follow nouns in Indonesian. So buku kecil = “small book/notebook.” Putting the adjective first (kecil buku) is ungrammatical.

Is buku kecil the usual way to say “notebook”?

More specific and common:

buku catatan = notebook (generic).
buku catatan kecil or buku saku = small/pocket notebook. buku kecil is understandable but less specific.

What’s the difference between dicatat and tercatat?

dicatat = “is/was recorded” (focus on the action; someone did it).
tercatat = “is recorded/listed” (state/result or sometimes unintended). Example: Nama Anda sudah tercatat. Use dicatat when talking about the act of recording.

How do I say “already recorded” or “has been recorded”?

Add an aspect marker:

Neutral: Pembelian hari ini sudah dicatat di buku kecil.
Formal: Pembelian hari ini telah dicatat di buku kecil.

Should I use mencatatkan/dicatatkan here?

Usually no. mencatat is the normal “to record.” mencatatkan means “to register/enter something (officially), often on someone’s behalf” (causative). Its passive is dicatatkan. Use these in formal contexts like mencatatkan pernikahan (register a marriage).

Is pada hari ini acceptable instead of hari ini?

Grammatically yes, but it’s formal/ceremonial (“on this day”). For everyday “today,” just use hari ini.