Learn Hardcore Indonesian: Dia mengira pelatihan dimulai besok, padahal dimulai hari ini. - He/She assumes the training starts tomorrow, whereas it starts today.

bolded padahal signals that the second clause states a fact that contradicts an expectation or assumption in the first clause. A natural English rendering is “but in fact,” “whereas (in reality),” or “though.” The nuance is corrective: it highlights that the earlier belief was wrong or unfitting with the reality. In this sentence: He/She thought the training starts tomorrow, but in fact it starts today.

Can I replace bolded padahal with bolded tetapi or bolded tapi (both mean “but”)?

Yes, and it’s grammatical: bolded Dia mengira pelatihan dimulai besok, tetapi/tapi dimulai hari ini. However, bolded tetapi/tapi is a neutral “but,” while bolded padahal adds the specific nuance “contrary to what was (wrongly) thought/expected.” If you just want a plain contrast, use bolded tetapi/tapi. If you want to stress the mistaken assumption, use bolded padahal.

How is bolded padahal different from bolded sedangkan?

bolded Sedangkan is “whereas/while” used to contrast two parallel situations, often with different subjects or topics, without implying anyone was wrong. Example: bolded Saya ke kantor, sedangkan dia ke kampus. In our sentence we are correcting a mistaken belief, so bolded padahal is the appropriate connector, not bolded sedangkan.

Could I use bolded ternyata instead of bolded padahal?

Yes: bolded Dia mengira pelatihan dimulai besok; ternyata dimulai hari ini. bolded Ternyata (“it turns out”) emphasizes the discovery of the real fact. bolded Padahal emphasizes that the earlier assumption doesn’t match reality. Both are common; avoid piling them together (bolded padahal ternyata) unless you have a stylistic reason.

Why is there no bolded bahwa after bolded mengira?

bolded Bahwa (“that,” introducing a clause) is optional with verbs of thinking/saying. All of these are correct:

bolded Dia mengira pelatihan dimulai besok.
bolded Dia mengira bahwa pelatihan dimulai besok. (more formal/explicit) Leaving out bolded bahwa is very natural.

What’s the difference between bolded dia, bolded ia, and bolded beliau?

bolded dia = he/she (gender-neutral), everyday neutral register, can be subject or object.
bolded ia = he/she, mostly used as a subject in formal/written style.
bolded beliau = he/she (honorific), used for respected people (teachers, elders, leaders).
So you could write bolded Ia mengira … (formal) or bolded Beliau mengira … when showing respect.

Why is bolded dimulai used instead of bolded mulai or bolded memulai?

bolded dimulai = passive “is/was started.” It focuses on the event beginning, not on who starts it. bolded Pelatihan dimulai hari ini = “The training starts today.”
bolded memulai = active, transitive “to start (something).” bolded Instruktur memulai pelatihan hari ini = “The instructor starts the training today.”
bolded mulai = intransitive “to start/begin,” or a preposition-like “starting from.” bolded Pelatihan mulai hari ini = “The training starts today.”
In your sentence, bolded dimulai is natural because we’re talking about when the event begins, without mentioning an agent.

Can I say bolded Pelatihan mulai besok/hari ini instead?

Yes. bolded Pelatihan mulai besok/hari ini is common and a bit more neutral/schedule-like. bolded Pelatihan dimulai … can feel slightly more formal or passive-voice-ish. Both are fine.

Where is the subject in bolded padahal dimulai hari ini? Shouldn’t bolded pelatihan be repeated?

Indonesian allows dropping elements that are clear from context. The understood subject is “the training.” You could explicitly say bolded padahal pelatihan itu dimulai hari ini for clarity, but repeating it isn’t required. The short form is very natural.

Does bolded dimulai here mean “starts,” “is starting,” or “started”? Indonesian doesn’t mark tense the same way as English.

All are possible depending on time expressions and context. Here, bolded hari ini anchors it to today, so the most natural reading is “starts today” or “is starting today.” If you want to emphasize completion, add bolded sudah/telah: bolded (ternyata) sudah dimulai hari ini = “(it turns out) it has already started today.”

Should I add bolded sudah or bolded telah in this sentence?

Only if you want to stress that the starting has already happened by the reference time. Compare:

bolded dimulai hari ini = starts today (neutral; could be later today or now).
bolded sudah/telah dimulai hari ini = has already started today (it began earlier today).

Is it okay to repeat the noun: bolded Dia mengira pelatihan dimulai besok, padahal pelatihan dimulai hari ini?

Yes, it’s grammatical, but a bit redundant. If you want to repeat it, make it more natural with a determiner: bolded … padahal pelatihan itu dimulai hari ini. In most contexts, the shorter original with ellipsis is preferred.

What’s the difference between bolded pelatihan, bolded latihan, and bolded kursus?

bolded pelatihan = (a) training program/workshop (often structured, possibly professional).
bolded latihan = practice/exercise/drill (the activity of practicing).
bolded kursus = a course (often a series of classes with a teacher, e.g., bolded kursus bahasa).
So “the training” in your sentence is best as bolded pelatihan.

Could I use bolded walaupun/meskipun instead of bolded padahal?

Not in the same structure. bolded Walaupun/meskipun means “although/even though” and typically heads a concession clause. You’d restructure: bolded Walaupun pelatihan dimulai hari ini, dia mengira mulai besok. That says “Although the training starts today, he/she thought it was tomorrow,” which changes the focus. bolded Padahal directly marks the earlier assumption as wrong in light of reality.

How would I say “would start tomorrow” explicitly?

Add bolded akan for futurity: bolded Dia mengira pelatihan akan dimulai besok, padahal dimulai hari ini. With bolded besok, bolded akan is optional; it just makes the future sense explicit.

Is there a casual/colloquial way to say this?

Yes, in speech you’ll hear:

bolded Dia kira pelatihan mulai besok, padahal hari ini. (drop bolded meng- and use bolded mulai)
First-person colloquial: bolded Kirain pelatihan besok, padahal hari ini. (bolded kirain = “I thought (but was wrong)”)
Avoid bolded Dia kirain …; bolded kirain is typically first-person.