Learn Hardcore Indonesian: Saya ragu bisa datang tepat waktu.

In Indonesian, ragu is an adjective meaning “doubtful/unsure,” but adjectives can function as predicates (like stative verbs). So Saya ragu means “I am doubtful.” It often takes a complement clause:

Saya ragu (saya) bisa datang tepat waktu.
Saya ragu apakah saya bisa datang tepat waktu. It also has related forms:
Noun: keraguan (doubt)
Transitive verb: meragukan (to doubt; also “questionable” as an adjective)
Passive: diragukan (to be doubted)

Why is the second saya omitted before bisa? Shouldn’t it be “Saya ragu saya bisa …”?

Indonesian commonly drops a repeated subject when it’s the same as the main clause subject. So Saya ragu (saya) bisa … is natural. Adding it—Saya ragu saya bisa datang tepat waktu—is also fine and can make the sentence more explicit.

Do I need a word like bahwa, kalau, or apakah to introduce the clause?

No, it’s optional. Variants:

More explicit/formal: Saya ragu bahwa saya bisa datang tepat waktu.
Informal: Saya ragu kalau saya bisa datang tepat waktu. (In speech, kalau often works like “that,” though in careful/formal writing, some avoid it here.)
“Whether”: Saya ragu apakah saya bisa datang tepat waktu.

Why is there no future marker like akan? Would adding it change the meaning?

Indonesian doesn’t require a future marker here; bisa already conveys “can/will be able to.” You can add it:

Neutral/formal: Saya ragu saya akan bisa datang tepat waktu.
Slightly stiff but acceptable: Saya ragu akan bisa datang tepat waktu. Colloquial future: bakal → Gue ragu bakal bisa datang tepat waktu.

Can I say “Saya ragu untuk datang tepat waktu”?

That means “I’m hesitant to come on time,” which is odd. Ragu untuk + verb expresses hesitation to do something (you’re holding back). For doubting ability/likelihood, use:

Saya ragu (saya) bisa datang tepat waktu.
Saya tidak yakin (saya) bisa datang tepat waktu.

What’s the difference between ragu and ragu-ragu?

ragu: doubtful/unsure (state of mind)
ragu-ragu: hesitant/indecisive (you’re wavering, can’t decide, often seen in behavior) Examples:
Dia ragu bisa menang. (He doubts he can win.)
Dia ragu-ragu memilih menu. (He hesitated to choose a menu.)

bisa vs dapat vs mampu vs sanggup vs boleh vs mungkin — which fits best here?

bisa: can/able; very common and neutral here.
dapat: can; a bit more formal or written. Saya ragu dapat datang tepat waktu.
mampu: capable (capacity/competence). Saya ragu mampu datang tepat waktu sounds odd; better with nouns: mampu untuk …
sanggup: up to it/able to bear; suggests effort/commitment. Saya ragu sanggup datang tepat waktu (uncommon here).
boleh: may/permission; not appropriate for ability.
mungkin: maybe/possible; not a verb of ability. Use to hedge: Mungkin saya tidak bisa datang tepat waktu.

Is “Saya ragu datang tepat waktu” (without bisa) okay?

It’s ambiguous and often reads as “I’m hesitant to come on time.” If you mean you doubt your ability/likelihood, prefer:

Saya ragu (saya) bisa datang tepat waktu.
Saya ragu (saya) akan datang tepat waktu.

What does “Saya ragu tidak bisa datang tepat waktu” mean? Is that a double negative?

It implies “I’m doubtful that I cannot come on time,” which suggests you think you probably can come on time—an odd nuance. If you mean you probably can’t, say:

Saya ragu (saya) bisa datang tepat waktu. (neutral-to-negative)
Sepertinya saya tidak bisa datang tepat waktu. (clear negative)

How can I make the sentence softer or more polite?

Add hedges/apologies:

Maaf, sepertinya saya tidak bisa datang tepat waktu.
Saya khawatir saya tidak akan bisa datang tepat waktu.
Kemungkinan saya terlambat.

What’s a more formal alternative?

Saya ragu dapat hadir tepat waktu. (use hadir and dapat)
Ada kemungkinan saya terlambat.
Saya tidak yakin dapat hadir tepat waktu.

Can I use aku or gue instead of saya?

Yes; it’s about register and region.

Neutral/polite: saya
Informal/intimate: aku
Jakarta colloquial: gue/gua Examples: Aku ragu bisa datang tepat waktu. / Gue ragu bisa datang tepat waktu.

How do I say “I doubt he can come on time”?

Saya ragu dia bisa datang tepat waktu. If you want to use a transitive verb:
Saya meragukan kemampuannya untuk datang tepat waktu. (natural) Avoid: Saya meragukan bahwa dia bisa … (not idiomatic in Indonesian).

Should I use datang, tiba/sampai, or hadir with tepat waktu?

datang: come (general) → datang tepat waktu is common for appointments.
tiba/sampai: arrive (end-point) → often for transport: Kereta itu tiba tepat waktu.
hadir: be present/attend (formal) → hadir tepat waktu sounds formal/courteous.

Is tepat waktu the only way to say “on time”? What about pas waktu?

Use tepat waktu for “on time/punctual.” Pas waktu is not the idiomatic way to say “on time.” Use pas for exact clock times: Kita mulai pas jam lima (“exactly at five”), but say tepat waktu for punctuality.