Khi (N)

Situations

S1: At 7 o'clock in the morning, Hà passed by the coffee shop and saw Nam and Lan sitting there.

Hà nhìn thấy họ khi đi ngang qua quán cà phê.
(Hà saw them while passing by the coffee shop.)

In this situation, khi is used to express a point of time in which an action or a state is occurring (nhìn thấy); that point of time goes together with a fact, an action, or a state (đi ngang qua).

S2: Last night, when Tân came back home at 12 o'clock, his wife was sleeping.

Tân về nhà khi vợ đã ngủ.
(Tân came back home as his wife was asleep.)

In this situation, khi vợ đã ngủ is considered as the period of time in which Tân came back home.

S3: Last night, at 12 o'clock when Tân came back home, his wife was sleeping.

Khi Tân về nhà, vợ anh đang ngủ.
(When Tân came back home, his wife was sleeping.)

In this situation, khi Tân về nhà is considered as a point of time in which his wife was sleeping.

Definition

Khi, as a noun, is used to express a point of time which goes together with a fact, an action or state.

  • khi and lúc: Khi and lúc can replace each other to indicate a point of time, but khi can't replace lúc to express a short period of time. Also, lúc can't replace khi to express conditional meaning. Cf:
[1] Khi / Lúc Tân về nhà, vợ anh đang ngủ.
    (When Tân arrived home, his wife was sleeping.)
[2] Đợi một *khi / lúc thì anh ấy về.
    (Wait a moment and he will return.)
[3] Xã hội sẽ tốt hơn khi / *lúc chính phủ biết quan tâm đến dân.
    (Society will be better when the government is more concerned about ordinary people.)

Combinations

  • một khi: Can be combined with đã... là / thì... to affirm a habit, a rule, or a certain thing.
[1] Một khi anh ấy (đã) hứa (là) anh ấy sẽ làm.
    (Once he promises something, he does it.)
  • mỗi khi... là...:
[2] Mỗi khi nó viết thư về nhà là tôi biết nó hết tiền.
    (Whenever he writes to his family, I know he's broke.)
  • có khi / có khi nào... không?: Perhaps, maybe; used to offer a prediction.
[3a] Trễ quá! Có khi anh ấy đã quên rồi.
     (It's so late! Perhaps he has forgotten.)
[3b] Trễ quá! Có khi nào anh ấy quên không?
     (It's so late! Might he by any chance have forgotten?)
  • ít khi: Seldom.
[4] Buổi sáng ít khi trời mưa.
    (It seldom rains in the morning.)
  • mấy khi: Rarely.
[5] Không cần mang theo áo mưa đâu, buổi sáng mấy khi mưa!
    (It isn't necessary to bring your raincoat; rarely does it rain in the morning!)
  • nhiều khi: Often.
[6] Công việc đơn giản quá, nhiều khi tôi cũng chán.
    (The work is so simple; I often get bored.)
  • đôi khi: Sometimes.
[7] Buổi tối, tôi thường ở nhà. Đôi khi tôi đến thăm bạn.
    (I usually stay at home in the evening. Sometimes I visit my friends.)
  • khi thì..., khi thì...:
[8] Công việc của tôi không đều, khi thì quá nhiều, khi thì quá ít.
    (My work isn't regular; at times it's too much, at other times it's too little.)