In Vietnamese, the phrase khi nào is used to express “when”. Literally, khi means “moment”, and nào means “which”.
Vietnamese is a wh-in-situ language, which means, in Vietnamese, the question words aren’t moved to the beginning of sentences, but rather stay in their original positions.
Structure
There are three possible positions for adverbials of time in Vietnamese, but the foolproof one to express “when” is at the beginning of sentences, so it is also the foolproof position for khi nào.
Khi nào + clause?
Note that if there is a preposition, such as “since” (“since when”), khi nào should be placed at the end of the sentence.
Examples
- Khi nào anh bắt đầu?When will you start?
- Anh ấy biết từ khi nào?Since when did he know?
- Họ ở Việt Nam tới khi nào?Until when are they going to stay in Vietnam?
Alternative form
Other phrases to express “when” are lúc nào and bao giờ.
- Anh học tiếng Việt từ lúc nào?Since when have you been learning Vietnamese?
- Bao giờ bố về?When will dad be back?
Usage note
There are three different phrases with giờ:
- bao giờ — when
- bao nhiêu giờ — how many hours
- mấy giờ — what time
Note that, while bao conceptually means “how many/much”, bao giờ never means “how many hours”.