Translation guide
How to express emphasis in questions, similar to 'on earth', 'in the world', etc.
Adding emphasis to a question word (who, what, where, why, how) to express surprise, frustration, or curiosity, like 'who on earth', 'what on earth', etc.
Placed before the question word to add emphasis. Very common and natural.
Who on earth said such a thing?
Kana version of 一体, often used in casual writing or when avoiding kanji.
Attached after a noun or clause to express surprise or disbelief, often rhetorical. Can be used in questions like 'Who on earth would...?'
I can't believe he would do such a thing. (Who on earth does he think he is?)
The English phrase 'on earth' is not translated literally into Japanese. Using 地球上で (chikyūjō de) would mean 'on the surface of the Earth', not the emphatic meaning.
一体 (ittai) comes before the question word. It can be used with 誰 (dare), 何 (nani), どこ (doko), いつ (itsu), なぜ (naze), どう (dō), etc.
How on earth did you get here?
いったい何が起こったの？
What on earth happened?
Stronger emphasis than 一体 alone, like 'in the world' or 'the heck'.
Why on earth did you do that?