Isn't it obvious? bộ … hả, chẳng phải … sao

Some questions aren't really questions: they mean "surely you know" or "isn't it obvious?". Vietnamese builds them from a negative, or chẳng phải, plus a question word at the end.

In Saigon, the everyday version starts with bộ and ends with hả: Bộ anh không biết hả? (You mean you didn't know?) Bộ signals surprise, as if the answer should be plain to see.

Chẳng phải … sao? (isn't it …? wasn't it …?) reminds someone of something they already know: Chẳng phải hôm qua chị dặn em rồi sao? (Didn't I remind you yesterday?)

In Hà Nội, and in writing, you'll also meet … không … hay sao? (don't you …, or what?): Anh không biết hay sao? And chẳng phải … là gì? (if that isn't …, what is?): Thế chẳng phải lừa đảo là gì? (If that isn't fraud, what is?)

Tone matters. Said gently, these questions just show surprise. Said sharply, they sound like a telling-off, so take care with older people and strangers.

Compare chẳng lẽ (surely not), which doubts something you'd rather not believe: Chẳng lẽ anh quên rồi? The forms here push the other way, towards "yes, of course". In writing, phải chăng (could it be that) does a calmer version of the same job.