while的用法及与when的比较小结
1. =when
2. =as long as
★while
3. =although
4. =whereas
1、(1) when表示at or during the time that, 既指时间点，也可指一段时间；从句中既可以用延续性动词，表示状态或时间段，也可以用非延续性动词，表示动作或时间点；while 表示during the time that，只指一段时间，从句中只能用延续性动词，表示状态或时间段。例如：
①Why do you want a new job when you've got such a good one already？（get为短暂性动词）你已经找到如此好的工作，为何还想再找新的？
②Sorry，I was out when you called me．（call为短暂性动词）对不起，你打电话时我刚好外出了。
③Strike while the iron is hot．（is为延续性动词，表示一种持续的状态）趁热打铁。
④The students took notes while they listened．（listen为延续性动词）学生们边听课边做笔记。
(2)在when或while所引导的状语从句中，如果从句的主语和主句的主语相同，且动词又是be动词时，从句的主语和be动词往往可以省略。例如：
When / While (I was) walking along the street，I heard my name called．
2、when和while都可以表示“尽管、虽然”，但when经常指描述的事实或结果事与愿违或出人意料，而while在语气上含有让步之意。例如：
§、The boy was watching TV when he should have gone to bed．
虽然那孩子该睡觉了，但他还在看电视。
【分析】：should have done本应该做某事，但事实上并没有，故此用when表示“事与愿违”。
§、While he loves his students，he is very strict with them．
虽然他爱他的学生，但对他们的要求也很严格。
【分析】：前提是他的确爱他的学生，但在此基础上一种委婉的让步，他还是对他的学生很严格，故此用while引导让步状语从句。
另外while还有以下用法：
(1) 然而，可是（=whereas）
I was preparing for the exam while they were chatting．
我在准备考试，可他们却在闲聊。
(2) 只要（=as long as）
While there is water, there is hope of life．
只要有水，就有生存的希望。
历年真题：
（09安徽）22. – I wonder how much you charge for your services.
-- The first two are free the third costs $30.
A. while
B. until
C. when
D. before
【解析】考查连词的用法。While在这里表转折,表示”但是”。前两个免费,而第三个则要收费。
（11安徽）28. Whatever is left over may be put into the refrigerator , _____ it will keep for two or three weeks.
A. when
B. which
C. where
D. while
【解析】考查定语从句。句意为：剩下的任何东西都可以放入冰箱，在那里可以保存两三周。本题考查非限制性定语从句的关系副词。由句型结构可以看出，该题中的先行词refrigerator在从句中作介词的宾语，该介宾结构在定语从句中作地点状语，故选择关系副词where。when在从句中作时间状语；which在从句中作主语或宾语；while是连词，不能用于定语从句。
（07安徽）21. The field research will take Joan and Paul about five months; it will be a long time _____ we meet them again.
A. after
B. before
C. since
D. when
（07山东）The book was written in 1946, _________ the education system has witnessed great charges.
A．when B．during which C．since then D．since when since when表示“从什么时候开始”
Summary 3 Past Co nti nuous Tense 过去进行时总结 I. Defin itio n 时态含义 表示过去某一时刻或过去一段时间内正在进行的动作。 II. Time words 时间标志词 1. then, at that time, this time yesterday, at 6 o ' clock yesterday ... 2. when/ while/ (just) as 引导的时间状语从句 III. Structure 动词结构 was/ were + doing ? Whe n/ while/ (just) as 引导的时间状语从句在过去进行时态中的用法区别 1. when既可以和短暂性动词连用，也可以和连续性动词连用, 句中一般翻译为“当...... 时候” / “就在那时”。 a. Some one kno cked at the door whenI was hav ing breakfast. b. I was tak ing a bath whenthe teleph one rang. 2. while只可以和连续性动词连用 句中一般翻译成“当...... 时候”(=wheri) / “然而”(强调前后两个动作同时进行) a. He cut himself while he was shaving. b. My wife was cooking the dinner while I was working in the garden. 3. (just) as 更强调“随着”，所引导的从句动作一般与主句动作伴随着发生。 a. Just as I was ope ning the front door, the teleph one rang. b. The children were singing as they went home.
when的用法总结大全 when的用法你知道多少，今天给大家带来when的用法，希望能够帮助到大家，下面就和大家分享，来欣赏一下吧。 when的用法总结大全 when的意思 adv. 什么时候,(用于时间的表达方式之后)在那时,其时,当时conj. 在…时,既然,如果 pron. 什么时候,那时 n. 时间，时候,日期,场合 when用法 when可以用作副词 when的基本意思是“什么时候”。可用作疑问副词,用来询问某事曾发生或将要发生的时间,引导特殊疑问句; 还可用作关系副词引导限制性定语从句、非限制性定语从句和表语从句,表示“是…时候的事”。 when可用作从属连词,引导状语从句,表示时间时作“当…时,在…的时候”解; 表示条件时作“如果,要是”解; 表示对比时作“既
然,考虑到”解。当when所引导的从句的主语和主句的主语一致时,常将其主语、系动词或助动词省去,只留实义动词或表语,或者改写为短语。 when所引导的时间状语从句用一般现在时代替将来时,用现在完成时代替将来完成时。 when用作副词的用法例句 When did that happen?那件事是什么时候发生的? They stood respectfully when he entered the room.当他走进房间时，他们都恭恭敬敬地站着。 Iron will melt when it is made very hot.当铁烧得很热时就会熔化的。 when可以用作连词 when可用作从属连词,引导状语从句,表示时间时作“当…时,在…的时候”解; 表示条件时作“如果,要是”解; 表示对比时作“既然,考虑到”解。当when所引导的从句的主语和主句的主语一致时,常将其主语、系动词或助动词省去,只留实义动词或表语,或者改写为短语。 when所引导的时间状语从句用一般现在时代替将来时,用现在完成时代替将来完成时。
when 和while的用法区别 两者的区别如下： ①when是at or during the time that, 既指时间点，也可指一段时间； while是during the time that，只指一段时间，因此when引导的时间状语从句中的动词可以是终止性动词，也可以是延续性动词，而while从句中的动词必须是延续性动词。 ②when 说明从句的动作和主句的动作可以是同时，也可以是先后发生；while 则强调主句的动作在从句动作的发生的过程中或主从句两个动作同时发生。 ③由when引导的时间状语从句，主句用过去进行时，从句应用一般过去时；如果从句和主句的动作同时发生，两句都用过去进行时的时候，多用while引导，如： a. When the teacher came in, we were talking. 当此句改变主从句的位置时，则为： While we were talking, the teacher came in. b. They were singing while we were dancing. ④when和while 还可作并列连词。when表示“在那时”；while表示“而，却”，表对照关系。如： a. The children were running to move the bag of rice when they heard the sound of a motor bike. 孩子们正要跑过去搬开那袋米，这时他们听到了摩托车的声音。 b. He is strong while his brother is weak. 他长得很结实，而他弟弟却很瘦弱。 一。引导时间状语从句时，WHILE连接的是时间段，而WHEN连接的多是时间点 例如What does your father do while your mother is cooking? What does your mother do when you come back? 二，WHILE可以连接两个并列的句子，而WHEN不可以 例如I was trying my best to finish my work while my sister was whtching TV 三，WHEN是特殊疑问词，对时间进行提问，WHILE不是。 例如，When were you bron? 续性动词和短暂性动词 英语中的动词，是学习中的重点，又是难点。英语中的动词有多种分类法。根据其有无含义，动词可分为实义动词和助动词；根据动词所表示的是动作还是状态，可以分为行为动词和状态动词；根据动词所表示的动作能否延缓，分为延续性动词和终止性动词。 可以表示持续的行为或状态的动词，叫做“延续性动词”，也叫“持续性动词”，如：be, keep, have, like, study, live, etc. 有的表示短暂、瞬间性的动词，叫做“终止性动词”，也可叫“短暂性动词”，或“瞬间性动词”，如die, join, leave, become, return, reach, etc.
when 和引导时间状语从句的从属连词when 是不同的。这主要表现在以下几个方面： 1. 位置：when 引导时间状语从句时，该从句可放在主句之前也可放在主句之后；而并列连词when 只能位于两个分句之间，而且前面常常有逗号。例如：Come when you please. 你高兴来就来吧。（when 为从属连词）When I saw him，he was writing to a friend of his. 我看见他时，他在给一个朋友写信。（when 为从属连词）I was taking a walk，when I came across him. 我正在散步，突然碰见了他。 2. 意义：when 作从属连词用时，它所引导的从句表示主句中谓语动词动作发生的时间，即作“当……时”解；而并列连词when 连接的两个分句中，第一个分句表示的是背景，第二个分句表示的是一种突然的、意想不到的情况或过早发生的事情。when 通常含“这时突然”之义。例如：I was thinking of this，when I heard my name called. 我正想着这件事，突然听到有人叫我的名字。I had just fallen asleep，when the boor-bell rang. 我刚入睡，门铃突然响了起来。这种意义在孤立的句子中可以理解到，在文章中更能体会得到。如在“ I was wandering through the street when I caught sight of a tailor's shop ”一句中，“在街头漫步”只是“看见有家缝纫店”的时间，其后作者怎样走进缝纫店，想要什么样的衣服，怎样受到伙计的奚落，又怎样受到老板的奉承等情景均与“漫步街头”没有直接的因果关系。 3. 时态：when 引导的时间状语从句中可以根据句意的需要用一般现在时.一般过去时、过去进行时、分别说明现在，过去，甚至将来的行为；并列连词when 后面的分句中通常用非延续性动词的一般过去时，其前表时间的分句中可用：（ 1 过去进行时表示过去某时间正在进行的动作。 例如： I was cooking when I heard her knocking at the door. 我正在做饭，突然听到她敲门的声音。 He was thinking about the problem，when an apple fell to the ground. 他正在思考这个问题，突然有一只苹果掉到了地上。 （2 ）was /were going to，was / were about to，was / were on the point of 表示过去某一时间将要发生的动作。 例如： I was just going when he came in. 我正要走，这时他就进来了。 We were about to start when it began to rain. 我们刚要动身天就开始下起雨来了。 He was on the point of leaving，when someone knocked at the door. 他刚要走就有人敲门。 （3 ）过去完成时表示过早发生的事情。请看下述两种场合： （a ）过去完成时和含否定意义的hardly，scarcely，nearly 连用，和just，little 连用，或者与否定词not 连用时，表示“刚……，就……”的意思。 例如： I had hardly opened the door when he hit me. 我刚一开门他就打了我一下。 I had nearly reached the town，when the young man suddenly said very slowly，“ Do you speak English ”我快要进城了，年轻人突然慢慢地说：“你会讲英语吗” I had been there little more than a week when I set to work in earnest. 我到那儿还不超过一个星期就开始认真干起活来。 I had not been reading for half an hour when I heard steps outside.
when和while的用法解析、练习题及答案（附总结表格） 一、讲解三例句: 1. The girls are dancing while the boys are singing. 2. Lucy’s mother is cooking when she gets home. 3. When/While Lucy’s mother is cooking, she gets home. 二、用when或者while填空 1.______ Margo was talking on the phone, her sister walked in. 2.______ we visited the school, the children were playing games. 3.______ Sarah was at the barber’s, I was going to class. 4.______ I saw Carlos, he was wearing a green shirt. 5.______ Allen was cleaning his room, the phone rang. 6.______ Rita bought her new dog; it was wearing a little coat. 7. He was driving along ________ suddenly a woman appeared. 8. _____ Jake was waiting at the door, an old woman called to him. 9. ______ it began to rain, they were playing chess. 10. She saw a taxi coming ______ the woman was waiting under the streetlight. 三、语法 while和when都是表示同时，到底句子中是用when还是while主要看主句和 从句中所使用 的动词是短暂性动作(瞬时动词)还是持续性动作。 1、若主句表示一个短暂性动作，而从句表示的是一个持续性动作时，用 When/While。如: He fell asleep when while he was reading. 他看书时睡着了。
when 的用法 一、when 用作副词。 1. 用作疑问副词，引导特殊疑问句。(什么时候，何时 [at what time ])例如： ①When will you come to see me? ②When are they going to visit the Great Wall? 2. 用作连接副词，通常用来引导名词性从句[主语从句、表语从句、同位语从句、宾语从句]及起名词作用的“when ＋动词不定式”结构。(什么时候，何时 [at which; on which ])例如： ①When he comes is not known. [主语从句] ②The morning is when I am busiest. [表语从句] ④I don't know when the plane takes off. [宾语从句] ⑤I don't know when to leave for London. [宾语] 3. 用作关系副词，引导限定性定语从句和非限定性定语从句。(在…的时候 [at/on/in/during which])例如： ①Do you still remember the days when we stayed in America? ②The day will come soon when the Chinese astronauts will go to the moon. ③It happened ten years ago, when I was a child. ④We will go to the countryside at the beginning of June, when the summer harvest will start. 二 . when 用作连词。 1. 用作从属连词，意为“当……的时候[at the time when ]”，引导时间状语从句。例如： ①They learned a lot from the peasants when they stayed in the village. ②It was snowing when he arrived at the station. 【点津】如果 when 引导的从句中的主语和主句中的主语一致，且从句中的谓语动词是“be ＋分词”或从句主语是 it ，则 be 动词及其主语常可省略。例如： ③When（ he was ）asked why he was late, he made no answer. ④I'll tell him about it when（ it is ）possible. 2. 用作从属连词，意为“一……就……”，引导时间状语从句。[immediately after]例如： ①We will stand up when the teacher comes into the classroom. 老师一进教室我们就起立。 ②Fire the rockets when I give the signal. 3. 用作从属连词，意为“还没 / 刚刚/刚一……就”，引导时间状语从句。[immediately after]例如： ①I had hardly opened the door when he came in. 我刚一开门，他就进来了。 ②I had not been reading for half an hour when I heard someone call my name. 【点津】hardly…when和no sooner…than的结构要注意三点：意思为“一A就B“；A句通常用完成时态；hardly 和 no sooner 位于句首时要注意部分倒装。 4. 用作从属连词，意为“倘若，如果”，表示条件。例如： ①Turn off the switch when anything goes wrong with the machine. 如果机器发生故障，就把电源关上。 ②He will be likely to recover when he is operated on. 5. 用作从属连词，意为“既然，尽管”，表示让步。例如： ①Why use metal when you can use plastic?既然能用塑料,为什么用金属? ②They kept trying when they knew it was hopeless. 尽管他们知道那件事没有希望，可是他们还在不断地努力。6. 用作并列连词，意为“在那时，届时;就在这时”，表示时间。这时主句中可以用过去进行时，过去完成时或“ was/were about to do sth. ”结构。 ①Last night I was about to go to bed when the phone rang. ②I was cooking in the kitchen when someone knocked at the door. ③He had just finished the book when supper was served. 7. 用作并列连词，意为“虽然、然而、可是”，表示转折。例如： ①He usually walks to work when he might take a bus. 虽然他可 以坐公共汽车上班，但他却常常步行上班。 ②I had only twenty dollars when I needed thirty to buy the dictionary.我需要 30 美元买那本字典，可是我只有20美元。 8. 用作并列连词，意为“而、却”，表示对比。例如： How can he say that everything is fine when it's obvious that it is not? 他怎能说一切都好呢？情况显然不是那样。 三 . when 用作代词[which time]。 when 作为代词常常位于介词之后，意为“那时，什么时候”。例如： ①Since when have you been studying Japanese? 【点津】since when 作引导词时是“介词（since）+关系代词（when）”的结构，when意为which time。since when常引导非限制性定语从句，从句应用完成时态。 ②I came here in 1949, since when I have been engaged in this work. 我1949年到这里，从那时起我就担任这项工作。 ③We came back on Tuesday, since when we have been working in the repair shop. ④We came a week ago, since when the weather has been bad. 四、when 还可用作名词，前面常常用定冠词 the。 the when 表示事 件发生的时间,常常与 the where, the how 并列使用。 He told the police the when and the how of the accident. 他告 诉警察事故发生的时间及发生的原委。 ［巩固练习］ 1. I remember ______ this used to be a quiet village. A. when B. how C. where D. what 2. Why do you want a new job _____ you've got such a good one already? A. that B. where C. which D. when 3. It was an exciting moment for these football fans this year, ______ for the first time in years their team won the World Cup. A. that B. while C. which D. when 4. We are living in an age _______ many things are done on computer. A. which B. that C. where D. when 5. The reporter said that the UFO ______ east to west when he saw it. A. was travelling B. travelled C. had been travelling D. was to travel 6. ______ got into the room _________ the telephone rang. A. He hardly had; then B. Hardly had he; when C. He had not; than D. Not had he; when 7. ---- Can I join your club, Dad? ---- You can when you _______ a bit older. A. get B. will got C. are getting D. will have got 8. I shall never forget those days ________ I lived in the countryside with the farmers, ________ had a great effect on my life. A. that; which B. when; which C. which; that D. when; who 9. The film brought the hours back to me ______ I was taken good care of in that faraway village. A. until B. that C. when D. where 10. He was about to tell me the secret ______ someone patted him on the shoulder.
WHEN与WHILE用法区别 when, while这三个词都有"当……时候"之意，但用法有所不同，使用时要特别注意。 ①when意为"在……时刻或时期"，它可兼指"时间点"与"时间段"，所引导的从句的动词既可以是终止性动词，也可是持续性动词。如： When I got home, he was having supper.我到家时，他正在吃饭。 When I was young, I liked dancing.我年轻时喜欢跳舞。 ②while只指"时间段"，不指"时间点"，从句的动词只限于持续性动词。如：While I slept, a thief broke in.在我睡觉时,盗贼闯了进来。 辨析 ①when从句与主句动作先后发生时，不能与while互换。如： When he has finished his work, he takes a short rest.每当他做完工作后，总要稍稍休息一下。(when = after) When I got to the cinema, the film had already begun.当我到电影院时，电影已经开始了。(when=before) ②when从句动词为终止性动词时，不能由while替换。如： When he came yesterday, we were playing basketball.昨天他来时，我们正在打篮球。 ③当从句的谓语是表动作的延续性动词时，when, while才有可能互相替代。如：While / When we were still laughing, the teacher came in.正当我们仍在大声嬉笑时，老师进来了。 ④当从句的谓语动词是终止性动词，而且主句的谓语动词也是终止性动词 时,when可和as通用，而且用as比用when在时间上更为紧凑，有"正当这时"的含义。如： He came just as (or when) I reached the door.我刚到门那儿，他就来了。 ⑤从句的谓语动词如表示状态时，通常用while。如： We must strike while the iron is hot.我们应该趁热打铁。 ⑥while和when都可以用作并列连词。
并列连词when相关的句式归纳 2006年普通高等学校招生全国统一考试(辽宁卷)中有这样一道单项填空题:He was about halfway through his meal ___ a familiar voice came to his ears. A.why B.where C.when D.while 解析:答案是C。此处when作并列连词,表示“就在此刻(and just then)”“,突然(and suddenly)”,该句译为：“饭刚吃到一半儿的时候，熟悉的声音传到了他的耳朵里。” 这里when引导的并不是我们所认为的时间状语从句而是并列句。when的意思是这时而不是当什么时候。在这个句型中when所引导的从句恰恰是句意的重心，when在这里起到一个修辞的作用表示后一动作的发生的出乎意料，而前面一句是为后一句谓语动词的发生提供背景。when 为并列连词。在我们的教材中并不鲜见。如： I'd just about given myself up for lost when I was spotted by a ship. 我正感到绝望时，一艘船发现了我。【Unit 3 Book 3】 33. She had just finished her homework ___ her mother asked her to plactised playing the piano yesterday.【09福建卷】 A. when B. while C. after D. since 7. Tom was about to close the window ___ the attention was caught by a bird. 【10全国卷】 A. when B. if C. and D. till 1．be (just) about to do... when... She was just about to say something more when she noticed the sullen look on his face．她刚要再说些什么，却突然看到了他阴沉的脸色。 We were about to telephone you when your telegram arrived. 2．be (just) on the point of doing sth ... when... They were on the point of giving up when the captain encouraged them fiercely to save the ship． 就在他们快要放弃努力时, 船长鼓励他们竭尽全力挽救轮船。
最新英语连词用法总结(完整) 一、单项选择连词 1．Read this story, you will realize that not everything can be bought with money. A．or B．and C．but D．so 【答案】B 【解析】 试题分析：考查并列句。句意看看这个故事，你就会明白不是所有的东西都可以用钱买到的。“祈使句 + and/or +陈述句”是一个固定句式，根据句意，选B 考点 : 考查并列句。 2．To live in honor, he came from a poor family, was his ambition. A．though B．if C．unless D．however 【答案】A 【解析】though尽管if如果;是否unless除非however无论怎样,根据题意他的野心就是为了有尊严的活着,尽管他来自一个贫穷的家庭.故选A. 3．He was about to tell me the secret __ _____ someone patted him on the shoulder. A．as B．until C．while D．when 【答案】D 【解析】 试题分析：句意：她正要告诉我这个秘密，这时有人拍了一下她的肩膀。beabouttodo...when...是固定句型，意为“正要做……这时……”。 考点：考查连词。 【名师点睛】 用when引导时间状语从句的句型结构搭配 beabouttodosthwhen刚要,即将；正要做某事,突然发生其他事 bedoingsthwhen正在做某事突然 haddonesthwhen刚刚做过某事突然 beatthepointofdoingsthwhen就在做某事的关键时刻突然 scarcely...when/hardly...when几乎未来得及就…；刚一……就…… nosooner...than一……就…… 4．I’m sorry I got caught in the traffic；_________, I could have been here sooner．A．besides B．although C．anyway D．otherwise 【答案】D 【解析】考查含蓄虚拟条件句。I could have been here sooner是和过去事实相反的虚拟语
as when while 的区别和用法 as when while的用法 一、as的意思是“正当……时候”,它既可表示一个具体的时间点，也可以表示一段时间。as可表示主句和从句的动作同时发生或同时持续，即“点点重合”“线线重合”；又可表示一个动作发生在另一个动作的持续过程中，即“点线重合”， 但不能表示两个动作一前一后发生。如果主句和从句的谓语动词都表示持续性的动作，二者均可用进行时，也可以一个用进行时，一个用一般时或者都用一般时。 1、As I got on the bus，he got off. 我上车，他下车。（点点重合）两个动作都是非延续性的 2、He was writing as I was reading. 我看书时，他在写字。（线线重合）两个动作都是延续性的 3、The students were talking as the teacher came in. 老师进来时，学生们正在讲话。（点线重合）前一个动作是延续性的，而后一个动作时非延续性的 二、while的意思是“在……同时（at the same time that )”“在……期间(for as long as, during the time that）”。从while的本身词义来看，它只能表示一段时间，不能表示具体的时间点。在时间上可以是“线线重合”或“点线重合”，但不能表示“点点重合”。例如： 1、He was watching TV while she was cooking. 她做饭时，他在看电视。（线线重合） 2、He was waiting for me while I was working. 我工作的时候，他正等着我。（线线重合） 3、He asked me a question while I was speaking. 我在讲话时，他问了我一个问题。（点线重合）
一、作为副词，它有以下的用法： 1. 作为疑问副词，引导特殊疑问句，意为“什么时候；何时”。 （1 ）When will they come back？ （2 ）What time will they come back？ 回答when 引导的从句，不一定指出具体的时间点。如回答句（ 1 ）可用tomorrow，next month 等。而回答what time 引导的问句，则必须说出具全的时间点，如at two o'clock，at five past ten 等。 2. 作连接副词，引导名词性从句或不定式，意为“什么时候”。从句使用陈述句语序，时态根据实际情况而定。 （1 ）I'd like to know when they will come. 我想知道他们什么时候来。（when 引导宾语从句） （2 ）Can you tell me when the bank opens？你能告诉我银行什么时候开门吗？（when 引导宾语从句） （3 ）When she'll be back depends much on the weather. 她何时回来在很大程度上取决于天气。（when 引导主语从句） （4 ）Have you decided when to go sightseeing？你们已经决定什么时候去郊游了吗？（when 引导不定式结构） 3. 作疑问代词，常和介词since，till，up to 等连用，意为“什么时候”。 如：（1 ）Since when have they had the house？他们从什么时候起有这幢房子的？（2 ）Till when is the library open？图书馆开放到几点呢？ 4. 作关系副词，引导限制性定语从句和非限制性定语从句。 （1 ）The days are gone forever when the Chinese people were looked down upon. 中国人民被人轻视的日子一去不复返了。 （2 ）The main school holidays are from mid-December till early February，when the days are long and warm. 学校的主要假期是从12 月中旬到2 月初，这段时间里白天长而且很温暖。 （3 ）Considering （the time）when these paintings were done，they are in excellent condition. 考虑到这些油画的创作时期，它们保存的状况是极好的。 （4 ）Do you remember （the time）when the three of us went on a picnic？你还记得我们三个人去野餐的那段时光吗？ A. 在定语从句中，that 在某些条件下可用来代替when ，这时其先行词通常是time，
我手里关于when用法的资料全再这了. 一、 when 意为“当…时”,用作连词,引导时间状语从句,从句的谓语动词可以是延续的（此时相当于while）,也可以是非延续性的.引导的时间状语从句通常用现在时表将来. I will write to my sister when I have finished the book.我读完这本书后便给姐姐写信. When he sees the photo,he can't help thinking of his childhood. 每当看到这张照片,他就不禁想起童年. 二、 when 引导时间状语时,若主从句主语一致或从句主语为it且从句谓语动词含be的形式,可省略从句的主语及be 部分. When (I was) walking on the street,I came across Mary.我在街上漫步时遇上了玛丽. He gave good practical advice when (he was) asked.他有求必应,给出了好的可行性建议. She would weep when (she was) alone.她孤独时便哭. When（you are）in trouble,you can ask her for help.有麻烦时,你可找她帮忙. We will do that only when ( it is) necessary.只有当有必要时我们才会那么做. 三、 when用作连词,表突然发生某事,意为“就在这时/那时”（=at this/that time）,常构成句型be doing…when…或be about to do…/be on the point of doing…when…. I was just coming along to see you when I ran into Tom.遇见汤姆时,我正在来看你的路上. He was about to go to bed when the telephone rang.他准备睡觉时电话铃响了. 四、 When用作连词表过早发生某事,意为“还没（刚刚）…就”,可构成句型hardly/scarcely…when….使用该句型时应注意两点：①主句的谓语动词用过去完成时,从句谓语动词用过去时.②若hardly/scarcely 位于句首时,其后的句子部分倒装,而when引导的从句不倒装. I had been there little more than a week when I set to work in earnest. 我在那还不到一个星期就开始认真工作. Hardly had I opened the door when he hit me.我一打开门他就撞了我. 六、 when引导条件状语从句,意为“在…情况下；如果；要是”,相当if. Why do you walk when you have a car?你有车为什么还走路呢? No one can make a dress when they haven't learnt.没有人能够不学就能制作衣服的. 七、 when 引导时间状语从句,意为“一…就…”,相当于as soon as . We will start when everything is ready.一切准备好了我们就出发. When she comes,I will give it to her.她来了我就给她. 八、 when可引导原因状语从句,意为“既然；考虑到…”,相当于since,as 或now that. You can't go home when you haven't finished your work. 既然你没完成工作,你就不可以回家. 九、 when可引导名词性从句或接不定式. Could you tell me when you will leave for Shanghai?能告诉我你什么时候去上海吗? Ask him when to open it.告诉他什么时候打开. 十、
when 用法小结 不管是在口语中，还是在书面语中，when是一个十分活跃的词，该词主要用作连词和副词，但是在意义方面其用法比较复杂。 一、作副词 1. 作疑问副词，用于构成特殊疑问句，意为“什么时候；何时”。 When will they come back？他们什么时间回来？ When can you finish the work? 你什么时间能完成这项工作？ 2. 作连接副词，引导名词性从句，或与不定式连用，意为“什么时候”。 Can you tell me when the bank opens？你能告诉我银行什么时候开门吗？ When she'll be back depends on the weather. 她何时回来取决于天气。 Have you decided when to go sightseeing？你们已经决定什么时候去郊游了吗？ 3. 作关系副词，引导定语从句。 The main school holidays are from mid-December till early February，when the days are long and warm. 学校的主要假期是从12 月中旬到2 月初，这段时间里白天长而且很温暖。 Do you remember the time when the three of us went on a holiday in Guilin？ 你还记得我们三个人在桂林度假的那段时光吗？ 二、作从属连词，引导状语从句。 1. 表示时间，意为“当……时；在……的时候”。 When you see him, please say hello to him. 见到他时，代我问他好。 When I reached the station，the train had left. 当我到达火车站时，火车已经开走了。 2. 表示条件，相当于if。 How can I get a job when I can't even read or write？
When while as的区别和用法 when的用法 当主句使用持续性动词时. Dave was eating,when the doorbell rang.门铃响时,大卫在吃饭. 2.一个动作紧接着另一个动作发生. When the lights went out, I lit some candles.灯灭了,我赶紧点上一些蜡烛. 3.谈论生命中的某一阶段,或过去的某段时间. His mother called him Robbie when he was a baby. 在他很小时,他妈妈叫他Robbin. 4.指"每一次" When I turn on the TV, smoke comes out the back. 每当我打开电视,就有烟从后面冒出. while/as 的用法 从句多为进行时,而且为持续性动词. I'll look after the children while you are making dinner. 你做饭,我来照顾孩子. 注意事项: (1) “主短从长”型：主句表示的是一个短暂性动作，从句表示的是一个持续性动作，三者都可用： He fell asleep when [while, as] he was reading. 他看书时睡着了。 Jim hurt his arm while［when，as］he was playing tennis. 吉姆打网球时把手臂扭伤了。 As［When，While］she was waiting for the train，she became very impatient. 她在等火车时，变得很不耐烦。 (2) “主长从长”型：若主、从句表示两个同时进行的持续性动作，且强调主句表示的动作延续到从句所指的整个时间，通常要用while： Don’t talk while you’re eating. 吃饭时不要说话。 I kept silent while he was writing. 在他写的时候，我默不做声。 但是，若主从句表示的两个同时进行的动作含有“一边…一边”之意思，通常用as：