Learn Hardcore Indonesian: Infeksi paru-paru itu berat bagi kakek saya. - That lung infection is serious for my grandfather.

Infeksi paru-paru itu ≈ that lung infection / the lung infection.
It suggests the speaker and listener both know which infection is being talked about (for example, one already mentioned in the conversation).

You can say Infeksi paru-paru berat bagi kakek saya, but it sounds more generic (lung infections in general are heavy/serious for my grandfather), not about a particular infection. So itu adds the idea of a specific, known infection and is quite natural here.

Why is berat used here? I thought berat means heavy, not serious or severe.

In Indonesian, berat literally means heavy, but it is very commonly extended to mean:

serious (for illness, problem)
severe
difficult, tough, hard to bear

Some examples:

Penyakitnya cukup berat. – His/her disease is quite serious.
Masalah ini sangat berat. – This problem is very tough/serious.
Tugasnya berat. – The task is hard/demanding.

So in Infeksi paru-paru itu berat bagi kakek saya, berat naturally means serious / hard to bear for the grandfather, not physically heavy.

Could I use another word instead of berat, like parah or serius? Would the meaning change?

Yes, you can, but there is a nuance:

berat – serious, hard to bear (focus on how burdensome or severe it feels)
parah – quite severe/bad (focus on the seriousness of the condition itself)
serius – serious (often a bit more formal or influenced by English)

Possible alternatives:

Infeksi paru-paru itu parah bagi kakek saya.
→ Emphasizes that the infection itself is severe for him.
Infeksi paru-paru itu sangat serius bagi kakek saya.
→ A little formal; could be used by a doctor, for example.

The original berat sounds very natural and idiomatic in everyday Indonesian.

Why don’t we need something like “is” in the sentence? Why not Infeksi paru-paru itu adalah berat?

Indonesian normally does not use a verb “to be” before adjectives.

The basic pattern is:

[Subject] + [adjective]
Infeksi paru-paru itu berat. = That lung infection is serious/heavy.

Adalah is mostly used to link:

a subject to a noun phrase:
Dia adalah dokter. – He/She is a doctor.
or in very formal definitions.

With adjectives, adalah is usually not used, so:

Infeksi paru-paru itu berat is natural.
Infeksi paru-paru itu adalah berat sounds unnatural in ordinary speech and most writing.

Why is there no word for “a” or “the” before infeksi? How do I know if it means “a lung infection” or “the lung infection”?

Indonesian has no articles like a/an/the.

Specificity is shown by context and particles like itu (that/the) and ini (this).

Infeksi paru-paru – could be a lung infection (generic).
Infeksi paru-paru itu – that/the lung infection (a specific, known one).

In this sentence, itu is what carries the idea of the/that. There’s no separate word for a; you just rely on context.

What exactly is paru-paru? Why is the word repeated with a hyphen?

Paru-paru means lungs.

The repetition is an example of reduplication, a very common process in Indonesian. Sometimes it marks plurality, but often (as here) it’s just the standard form of the word:

paru-paru – lungs (a body organ; treated as a single unit, like “the lungs”)
As a standalone, paru is not commonly used in everyday language for “lung”; paru-paru is the normal form.

Spelling: it is correctly written with a hyphen: paru-paru.

Is paru-paru grammatically singular or plural? How would you say one lung or two lungs?

In practice, paru-paru is treated as the name of the organ “lungs”; Indonesian doesn’t force you to choose singular/plural in the same way English does.

If you need to be specific:

satu paru-paru – one lung (used in medical or precise contexts)
dua paru-paru – two lungs

But in most cases:

paru-paru alone just means the lungs as an organ, without emphasizing number. The grammar doesn’t change between singular and plural.

Can I move bagi kakek saya to the front or the middle of the sentence? For example: Bagi kakek saya, infeksi paru-paru itu berat?

Yes, Indonesian word order is fairly flexible for prepositional phrases like bagi kakek saya.

All of these are grammatically fine:

Infeksi paru-paru itu berat bagi kakek saya.
– Neutral order; very natural.
Bagi kakek saya, infeksi paru-paru itu berat.
– Puts extra emphasis on for my grandfather (from his perspective).

You generally would not split the noun phrase:

✗ Infeksi bagi kakek saya paru-paru itu berat. – unnatural.

So: front or end is fine; don’t break up Infeksi paru-paru itu.

Why is bagi used here to mean “for”? Could I use untuk or kepada instead?

All three mean “for/to” in some contexts, but they’re used differently:

bagi – “for (someone)” in the sense of from their perspective / as far as they’re concerned / as a burden or benefit to them.
→ Very natural here: berat bagi kakek saya = hard/serious for my grandfather.
untuk – “for” in a more general, purpose/intended-for sense:
- Obat ini untuk kakek saya. – This medicine is for my grandfather.
- You can say berat untuk kakek saya and be understood; it’s not wrong, but bagi sounds a bit more idiomatic in “difficult for (someone)” statements.
kepada – “to” someone (for giving, saying, addressing):
- Dokter berbicara kepada kakek saya. – The doctor spoke to my grandfather.
- berat kepada kakek saya is not natural.

So in this sentence, bagi is the best choice.

What does kakek saya literally mean? How is it different from kakekku?

kakek – grandfather
saya – “I/me” (formal/neutral)
kakek saya – literally “grandfather I” → my grandfather.

kakekku is a clitic form:

-ku means “my”
kakekku also means my grandfather, but:
- sounds slightly more informal and personal
- is common in speech and casual writing.

In neutral/formal contexts, kakek saya is safer. In a text message or a story with a personal tone, kakekku is very natural.

In conversation, could kakek by itself mean my grandfather, or do I always need saya/ku?

In many real-life contexts, kakek by itself can be understood as my grandfather, when it’s clear you’re talking about your own family. For example:

Kakek sakit. – Grandfather is sick. (Commonly understood as “My grandfather is sick,” if you’re talking about your own situation.)

However, in a sentence like Infeksi paru-paru itu berat bagi kakek, without context it’s less clear whose grandfather you mean. Using kakek saya or kakekku:

removes ambiguity
sounds complete and natural in isolation, like in your example sentence.

How would I show that this was in the past, like “That lung infection was hard for my grandfather”, since there is no past tense marker?

Indonesian does not change the verb or adjective for tense. You show time by adding time expressions or context words.

Some options:

Dulu, infeksi paru-paru itu berat bagi kakek saya.
– In the past, that lung infection was hard for my grandfather.
Waktu itu, infeksi paru-paru itu berat bagi kakek saya.
– At that time, that lung infection was hard for my grandfather.
Infeksi paru-paru itu dulu berat bagi kakek saya.

Without any time expression, Infeksi paru-paru itu berat bagi kakek saya can mean:

is hard now, or
was hard then,
depending on the wider context of the conversation.