when,while這兩個詞都有"當(dāng)……時候"之意,但用法有所不同,使用時要特別注意.
①when意為"在……時刻或時期",它可兼指"時間點"與"時間段",所引導(dǎo)的從句的動詞既可以是終止性動詞,也可是持續(xù)性動詞.如：
When I got home,he was having supper.我到家時,他正在吃飯.
When I was young,I liked dancing.我年輕時喜歡跳舞.
②while只指"時間段",不指"時間點",從句的動詞只限于持續(xù)性動詞.如：
While I slept,a thief broke in.在我睡覺時,盜賊闖了進(jìn)來.
辨析
①when從句與主句動作先后發(fā)生時,不能與while互換.如：
When he has finished his work,he takes a short rest.每當(dāng)他做完工作后,總要稍稍休息一下.(when = after)
When I got to the cinema,the film had already begun.當(dāng)我到電影院時,電影已經(jīng)開始了.(when=before)
②when從句動詞為終止性動詞時,不能由while替換.如：
When he came yesterday,we were playing basketball.昨天他來時,我們正在打籃球.
③當(dāng)從句的謂語是表動作的延續(xù)性動詞時,when,while才有可能互相替代.如：
While / When we were still laughing,the teacher came in.正當(dāng)我們?nèi)栽诖舐曟倚r,老師進(jìn)來了.
④當(dāng)從句的謂語動詞是終止性動詞,而且主句的謂語動詞也是終止性動詞時,when可和as通用,而且用as比用when在時間上更為緊湊,有"正當(dāng)這時"的含義.如：
He came just as (or when) I reached the door.我剛到門那兒,他就來了.
⑤從句的謂語動詞如表示狀態(tài)時,通常用while.如：
We must strike while the iron is hot.我們應(yīng)該趁熱打鐵.
⑥while和when都可以用作并列連詞.
Mike is tall while his brother is short.邁克的個子很高,然而他弟弟很矮.
Mary was on her way home when two big boys stopped her.瑪麗正走在回家的路上,這時兩個大個子男孩攔住她.