Translation guide
An emphatic phrase added to wh-questions to express surprise, disbelief, or strong curiosity. In Japanese, this is expressed with sentence-ending particles, adverbial phrases, or rhetorical constructions rather than a direct translation.
Express strong surprise or disbelief in a wh-question, like 'What in the world...?' or 'Why on earth...?'
The adverb いったい (一体) is the most common and neutral way to add emphasis to a wh-question. It can be used in both spoken and written Japanese, and is appropriate in most situations.
いったい何が起こったんだ？
What in the world happened?
いったいなぜ彼は来なかったの？
Why in the world didn't he come?
Adding んだ (casual) or のだ (formal) to a wh-question seeks an explanation and naturally conveys emphasis or strong curiosity. Often used with いったい for even stronger effect.
Express that something is impossible or absurd, like 'How in the world could I...?'
A rhetorical question pattern meaning 'How could I possibly...?' or 'As if I could...'. できるものか is casual; できようか is formal/literary.
どうしてそんなことができるものか。
How in the world could I do such a thing?
Literally 'there is no way that...', used to strongly deny possibility. Often corresponds to 'How in the world could...?' in English.
There is no direct Japanese equivalent of 'in the world' as a phrase. Avoid literal translations like 世界で (in the world) in this context, as they will sound unnatural. Use the patterns above instead.
いったい is an adverb that explicitly adds emphasis, while んだ is a sentence-ending pattern that seeks an explanation and naturally conveys curiosity or surprise. They are often combined for strong emphasis: いったい何をしているんだ？
何をしているんだ？
What in the world are you doing?
どうしてそんなことをしたのだ？
Why in the world did you do that?
The sentence-ending particle の (casual, often with rising intonation) or のか (more masculine/forceful) adds a tone of surprise or demand for explanation. Common in spoken Japanese.
どこに行くの？
Where in the world are you going?
誰がそんなことを言ったのか？
Who in the world said such a thing?
A more emphatic version of いったい, meaning 'what on earth' or 'what in the world'. Slightly more dramatic or exasperated.
一体全体どういうことだ？
What in the world is going on?
A rhetorical pattern that demands an explanation, often with frustration. というのだ is formal/written; っていうの is casual spoken.
なぜ今になって反対するというのだ？
Why in the world are you opposing it now?
彼がそんなことをするはずがない。
How in the world could he do such a thing? (There's no way he would.)