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I have been learning English for a long time, but still don't understand about the when/while difference and their usage.

When can I use "while"?

marked as duplicate by Edwin Ashworth, Drew, tchrist, andy256, anongoodnurse Jan 3 '15 at 8:02

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    Just an additional note to the answers you're receiving (which focus on the temporal sense of both words): "while" can be used to show contrast, similarly to "whereas." E.g. I enjoy going backpacking on vacation, while my wife prefers visiting big cities. – Rusty Tuba Jan 2 '15 at 15:53
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While describes a length of time.

If we compare various dictionaries, while is used to talk about an unspecific period of time, like when you ask your friend if you can borrow his notebook for a while.

  • at the same time that something is happening

    While in prison he shared a cell with Ron Spicer.
    
    Could you look after the children while I cook lunch?
    
  • used when comparing things, situations, or people

    While most children learn to read easily, some need extra help.
    
    The south of the country grows richer, while the north grows poorer.
    
  • formal used for saying that although you accept that something is true, there are also doubts or facts that you cannot ignore

    While I agree with you, I do not believe that your way is best.
    
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@Martin 's answer is generally correct, when is a specific moment (you can conceptualize it geometrically as a point), but while is a period of time (you can conceptualize it as a line). It is important to note however, that the "point" of time expressed by when may be fuzzy and large. For that reason it might be better to think of the distinction as being that while is generally used for things synchronized in time, where the simultaneous nature of their occurrence is important:

You can have a cookie when the bell rings means you can have a cookie after the bell signals you. You can have a cookie while the bell rings means you need to consume the cookie during the time the bell is ringing.

In the specific case of when I was a child it the usage is because we are conceptualizing childhood as a point of time. Compare when I was a child, the war was going on with while I was a child, the war was going on. The second version emphasizes two simultaneous things happening in parallel, the first locates one thing in relationship to another. The distinction is subtle, and largely a matter of choice.

  • Are these sentences interchangable with no remarkable difference in meaning: "When she was talking, he started to laugh", "While she was talking, he started to laugh", and "As she was talking, he started to laugh" – Englishfreak Jan 2 '15 at 15:47
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When generally refers to a specific moment of time, whereas while refers to a period of time.

  • So "when I was a child" doesn't refer to a period of time? – Robusto Jan 2 '15 at 15:11
  • Why do people say "When I was child.." not " While I was child.."? – Phil Jan 2 '15 at 15:12
  • People say both, Phil. – TRomano Jan 2 '15 at 15:27
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When - at that time.
While - during that time.

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Use While when you are still doing something or while something is happening

Use When at the time of doing something or when something has happened

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While implies a continuation of some state whereas when is a single condition.

While I may not be the smartest person in town, I still manage to get by.

When I am not smart in going about doing things, I find it is harder to get by.

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You can use while while you want to say when, and you can use when when you want to say while. Clear?

When pregnant refers to the condition qua if/then condition

While pregnant = refers to pregnancy qua ongoing condition

Since pregnancy is on ongoing condition, "when pregnant" strikes my ear as unidiomatic, but many people use them interchangeably.

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