区别辨析 as, when 与 while

as, when, while均可表示两个行动或情况同时发生，但又有某些区别：

(1) 表示“背景”。

当表示某事在另外一件事情正在进行中而发生时，可用as, when或while引出较长的(正在进行的)“背景”情况。该情况在此前开始，并可能在此后还要继续下去。

As/When/While I was walking down the street, I noticed a helicopter flying overhead.
当我正沿着大街走时，我看到一架直升机在头顶上空飞行。

＊这里要注意：

①用when时可接两个从句中的任一个。

John arrived when I was cooking lunch./ When John arrived I was cooking lunch.
我正做着午饭，约翰到了。/约翰到时，我正做着午饭。

②用when或while，通常接过去进行时表示较长的“背景”情况。

③用as时，有时可用一般过去时，尤其在较为正式的文体中(如文学作品的叙述中)。

As I sat thinking about my life, I began to realize that without it I could not have remained in London, would not have appeared at the minister's, never should have met her.
当我坐着思考着我的人生时，我开始意识到，没有它(此处指百万英镑的钞票，译者注) 我不可能留在伦敦，不会出现在牧师家里，也永远不会遇上她。

④as, when, while与现在进行时连用表示将来。

I hope you'll think of me for a moment as/when/while I'm taking my driving test.
我希望在我参加驾照考试时，你能考虑我。

(2) ①表示两个同时发生/进行着的较长行动、事件或情况时，最常用while，这时，一般过去时或过去进行时均可用。

While John was sitting/sat biting his nails, I was working out a plan to get us home.
当约翰坐着咬指甲时，我正筹划着能使我们回家的计划。

②在这种情况下，when, as不常用。但as 可用来表示两个发展着的或变化着的情况。

As I get older, I get more optimistic.
随着年纪增长，我变得更加乐观了。
As the champion grew weaker, his opponent's attacks became more and more violent.
随着这位冠军渐渐变弱，他对手的攻击越来越猛。

(3) 表示两个短的行动或事件在同时发生时，最常用as或just as, when也可用。

英文之旅