German Indirect Questions: ob and the W-Words in Subordinate Clauses

The ruleAn embedded question keeps its question word, or takes ob if it had none, and sends its verb to the end like any subordinate clause.

Yes/no questions become ob

A direct yes/no question has no question word, so German supplies one: ob, meaning whether.

Kommt er? → Ich weiß nicht, ob er kommt. Is he coming? → I don't know whether he's coming.
Hast du Zeit? → Er fragt, ob du Zeit hast. Do you have time? → He's asking whether you have time.
Ist das richtig? → Können Sie mir sagen, ob das richtig ist? Is that right? → Can you tell me whether that's right?

W-questions keep their word

Wann kommt er? → Ich weiß nicht, wann er kommt. When is he coming? → I don't know when he's coming. wann stays; kommt moves to the end.
Wo wohnst du? → Er fragt, wo du wohnst. Where do you live? → He's asking where you live.
Warum hat sie das gesagt? → Ich verstehe nicht, warum sie das gesagt hat. Why did she say that? → I don't understand why she said it. Two verb parts: the conjugated one goes last.

Direct	Indirect	Introduced by
Kommt er?	…, ob er kommt	ob
Wann kommt er?	…, wann er kommt	wann
Mit wem sprichst du?	…, mit wem du sprichst	the whole phrase moves
Worüber redet ihr?	…, worüber ihr redet	wo- compound

Why bother

Because a direct question can be blunt, and embedding it is the standard way of being polite. Wo ist der Bahnhof? is fine but bare; Können Sie mir sagen, wo der Bahnhof ist? is what people say to a stranger.

Entschuldigung, wissen Sie, wann der nächste Zug fährt? Excuse me, do you know when the next train goes?
Ich würde gern wissen, ob noch Plätze frei sind. I'd like to know whether there are still seats free.

Where it goes wrong

Ich weiß nicht, wann kommt er.

Ich weiß nicht, wann er kommt.

Embedding a question turns it into a subordinate clause, and subordinate clauses do not invert. The verb goes to the end, and the subject comes straight after the question word.

Common questions

What is the difference between ob and wenn?

ob means 'whether' and introduces an embedded question: 'Ich frage mich, ob das stimmt.' wenn means 'if' in the conditional sense, or 'when' for repeated events: 'Wenn das stimmt, ändert das alles.' English uses 'if' for both, which is why they get swapped.

Where does the verb go in an indirect question?

At the end, as in every subordinate clause. 'Wo wohnt er?' becomes 'Ich weiß nicht, wo er wohnt': the inversion of the direct question is undone and the verb drops to final position.

Why are indirect questions more polite?

Because they frame the request as a statement about your own knowledge rather than a demand on the listener. 'Können Sie mir sagen, wo …' softens the question the way English does with 'Would you happen to know …'.