before的用法
[思路分析] Before 在英语中是一个比较常用的虚词，它既可作介词或副词用，也可作从属连词用。
在近几年的高考试题中常常出现考查其从属连词用法的题目。
下面就把其作为从属连词的用法归纳如下：1. 表示“在…..之前就…..”。
Mary had finished her homework before her mother returned.2. 表示“过了多久后才…….. ，动作进行到什么程度才……” The man almost knocked me down before he saw me . They walked about 30 miles to the west before they saw a village . They worked day and night about three days before everything returned to normal .3. 表示“来不及； 尚未…..就…” Before I could get in a word , he had measured me . He ran off before I could stop him . She left the company before I could have a word with her .4. 表示“刚…就…” I had hardly sat down before the bell rang.5. 表示“不知不觉就…..； 还没弄清就……” Time passed quickly and three months went by before Aqiao knew it.6. 表示“宁愿…，决不…，与其…，毋宁….”常与will 或would 连用。
I would die before I would tell I'd shoot myself before I apologized to him. I would / will die before I surrender .7. 表示“否则；以免” Do it now before you forget . I will write it down before I forget it .8. 用于句型“it was +时间段+ before …” 表示 “过了多久才…” It was three days before he came back. .9. 用于句型 “ it was not long +时间段+ before …” 意为“不久就….” It was not long before he sensed the danger of the position .10. 用于句型“it will be(not )+时间段+ before….”表示“要过多久/ 不久…才…” It will be half a year before you graduate from this school . It will be not long before you find you are wrong .[解题过程] before和ago都能表示在一段时间以前，但是二者的内涵和具体用法有明显的区别： 1. before表示从过去或将来某一时间算起多少时间以前，由于与这一时间状语连用的行为先发生在过去或将来某一时刻之前，因此往往出现在过去完成时态或将来完成时态中。
例如： ① I called him up last night, but his mother told me he had left for Wuhan two days before. ② She said that she had married him five years before. 2.如果不具体表明多少时间以前，before意为“从前；以前”，表示从现在开始追溯到过去一段时间，或者主句的谓语动词表示的是经常、反复发生的行为，以副词的形式置于句末，可以用在现在完成时态中。
例如： ①I have never been to Beijing before. ②Have you ever seen a tiger before？ ③ I often go over the lessons that I have learned a few days before. 注意： before前的时间状语如果是特定的，含义不一样。
试比较： He said he had arrived here a day before. （一天前） He said he had arrived here the day before. （前一天） 3. ago指的是从现在起到过去时间的某一点的一段时间。
这个时间状语常与一般过去时态或过去进行时态连用。
例如： ① I graduated from the college twenty years ago. ②I was asked what I was doing a month ago. 4. 表示在某一时间点或事件以前时，只能用before，不用ago。
因为这种用法是将before当作介词或连词使用。
ago不具有这种功能。
例如： ① He will come back before eleven o'clock. ② Where did your brother study before he joined the army？ ③ It was hoped that this would be achieved before the year 2006. 5.按语法规则，ago只能与一般过去时连用，但在since three years ago这类短语中能与现在完成时态连用。
因为three years ago构成一个名词短语，共同作since的宾格，意为“自从三年前以来”。
例如： ① He has been here since three years ago. ② I have taught English in this school since twenty years ago. 6. 含before的从句一般不用将来时态，如果采用“will / would +V.”时，一般被认为是情态或虚拟语气。
例如： I would die before I would confess to it. 7.如果before从句是一般过去时态，所暗示的是过去发生的事，主句则宜用过去完成时，语义偏重于过去某阶段的行为或状况时，还可与一般过去时态连用。
例如： ① I had never seen a Red Army man before I arrived in Xi'an. ② They asked me things that happened before the boy was born. 8. 不少的语法书上说，before引导的从句习惯上不与否定的主句连用，要用until。
实际上二者都可以，有时在意义上有些区别。
试比较： He didn't arrive until I returned. 直到我回来时他才到达。
He did not arrive before I returned. 在我回来之前他尚未到达。
I didn't manage to do it until you had explained how. 直到你解释了如何干，我才设法完成了那项工作。
I didn't manage to do it before you had explained how. 你解释了如何干之后，我才设法完成了那件工作。
9. before在句中的含义比较灵活，虽然before引导的也是一个时间状语，但译成汉语时却不必死译为“在……以前”。
可以采取下面几种译法：（A）译为“……才”；（B）译为“……就”；（C）译为“尚未”、“还没有”、“来不及”、“不要”、“别”；（D）译为“在……的时候还没有”；...
关于before的用法的一个问题
before 可以和过去完成时连接。
下面是具体的内容。
你可以从中找到答案。
一。
过去完成时主要有以下几点用法： 1. 表示过去某一时间或动作之前已经发生或完成的动作或存在的状态。
句中常用by, before, when, until等词引导的时间状语。
它是以过去某一时间为起点，所以过去完成时是一个相对的时态，表示的是“过去的过去”。
只有和过去某时间或某动作相比较时才能用到它。
例如： Most of the guests had left when he arrived at the party. 当他到达晚会时，他发现大多数客人已经离开了。
2.过去完成时还可表示过去某一时刻之前发生的动作或状态持续到过去某个时间或持续下去，常与for, since等词连用。
例如： When Jack arrived, he learned Mary had been away for almost an hour. 当杰克到时，他得知玛丽已经离开快一个小时了。
3. 用于并列句：一个并列句用的是过去式，如果另一个并列句表示的动作早于过去式这一动作，这时需用过去完成时。
例如： Tom flew home, but his father had already died.汤姆乘飞机回家，他的父亲却已经去世了。
4. 某些动词的过去完成时表示过去未实现的希望、计划或打算。
常用的动词有hope, expect, suppose, think, want, wish等。
例如： They had hoped to be able to arrive before ten. 他们本来打算能在10点之前到达。
5. 在before, after, as soon as等引导的从句中，由于这些连词本身已经表示出时间先后，所以可以用过去时来代替过去完成时。
例如：二。
一般过去时和过去完成时用法有哪些不同？ 1. 在主从复合句中的用法不同 （1） 用在宾语从句中 在主句谓语为一般过去时的宾语从句中，既可用一般过去时，也可用过去完成时。
但两种时态的意义明显不同。
试比较下列两组句子： She said she was a doctor. 她说她是位医生。
（说话时仍为医生） She said she had been a doctor.她说她曾当过医生。
（说话时已不是） She said she had been a doctor for twenty years.她说她当过20年的医生。
（主要强调说话时已当过20年医生，此状态可能已经结束，也可能还没有） 但是，如果从句中有表示具体时间的状语，则常用一般过去时。
例如： He said he was born in 1986. 他说他是 1986年出生的。
（2） 用在含有after的主从复合句中 在含有after的主从复合句中，一般在从句中使用过去完成时，主句中使用一般过去时。
例如： After he had done his homework, he went out to play football. 因连词after本身能明确表示时间的先后关系，因而多数的主句和从句均使用一般过去时。
例如： After he arrived in England, Marx worked hard to improve his English. (3) 用在含有before的主从复合句中 用在含有before的主从复合句中，一般在从句中使用一般过去时，主句中使用过去完成时。
例如： Lily had written some letters before she went out shopping. 有时，也可以在从句中用过去完成时，主句中用一般过去时，这样就可使描述更为生动。
试比较： We got to the station before the train had left. 火车尚未开动之前，我们就到了车站。
We had got to the station before the train left. 火车开出之前，我们就已经到了车站。
像after一样， before本身就能明确地表示时间的先后关系，故多数主从句均使用一般过去时，而无需使用过去完成时。
例如： Many people left for home before the film ended.电影尚未放完，许多人就起身回家了。
（4） 用在含有when的主从复合句中 由于when本身不能明确表示时间的先后关系，故先发生的动作应用过去完成时，后发生的动作只需用一般过去时。
这样用过去完成时的可能是主句，也可能是从句。
例如： When all his money had been used up, Peter had to turn to a friend for help. 当他的钱全都用光时，彼得只好转而求助于一个朋友。
有时，主句和从句的谓语动词的先后关系十分明确，两个动作紧接着发生，前一动作导致后一动作，这时两者均用一般过去时即可。
例如： When the meeting was over, we left the hall. 散会后，我们就离开了大厅。
2. 叙述几个连续的动作用法不同 在叙述两个或两个以上接连发生的动作用and, but, so或then等连接并按时间发生的先后顺序叙述时，只需用一般过去时。
例如： She entered the room, turned on the light and found everything stolen. I lost my pen but soon found it. She lost her pen, so I lent her mine. 但是，如果两个先后发生的动作不是按时间的顺序排列或叙述时，为明确动作发生的先后顺序，先发生的动作就得用过去完成时。
例如： The farmers were in high spirits because they had got another good harvest. 农民们兴高采烈，因为他们又获得了一次好收成。
3. 表示与过去还是现在相反的情况不同 一些表示心理活动的动词，如think, know, expect, mean, hope, want, suppose等，用一般过去时可表示存在于过去而非现在的心理活动或事与愿违的情况。
例如： I didn't know you were here. 我不知道你在这儿。
而这些词的过去完成时则表示的是过去未曾实现的愿望、打算、想法或意图等。
例如： We had hoped that you would be able to visit us. 我们原本希望你去看我们。
before和ago的区别？
before和ago都能表示在一段时间以前，但是二者的内涵和具体用法有明显的区别： 1. before表示从过去或将来某一时间算起多少时间以前，由于与这一时间状语连用的行为先发生在过去或将来某一时刻之前，因此往往出现在过去完成时态或将来完成时态中。
例如： ① I called him up last night, but his mother told me he had left for Wuhan two days before. ② She said that she had married him five years before. 2.如果不具体表明多少时间以前，before意为＂从前；以前＂，表示从现在开始追溯到过去一段时间，或者主句的谓语动词表示的是经常、反复发生的行为，以副词的形式置于句末，可以用在现在完成时态中。
例如： ①I have never been to Beijing before. ②Have you ever seen a tiger before？ ③ I often go over the lessons that I have learned a few days before. 注意： before前的时间状语如果是特定的，含义不一样。
试比较： He said he had arrived here a day before. （一天前） He said he had arrived here the day before. （前一天） 3. ago指的是从现在起到过去时间的某一点的一段时间。
这个时间状语常与一般过去时态或过去进行时态连用。
例如： ① I graduated from the college twenty years ago. ②I was asked what I was doing a month ago. 4. 表示在某一时间点或事件以前时，只能用before，不用ago。
因为这种用法是将before当作介词或连词使用。
ago不具有这种功能。
例如： ① He will come back before eleven o'clock. ② Where did your brother study before he joined the army？ ③ It was hoped that this would be achieved before the year 2006. 5.按语法规则，ago只能与一般过去时连用，但在since three years ago这类短语中能与现在完成时态连用。
因为three years ago构成一个名词短语，共同作since的宾格，意为＂自从三年前以来＂。
例如： ① He has been here since three years ago. ② I have taught English in this school since twenty years ago. 6. 含before的从句一般不用将来时态，如果采用＂will / would +V.＂时，一般被认为是情态或虚拟语气。
例如： I would die before I would confess to it. 7.如果before从句是一般过去时态，所暗示的是过去发生的事，主句则宜用过去完成时，语义偏重于过去某阶段的行为或状况时，还可与一般过去时态连用。
例如： ① I had never seen a Red Army man before I arrived in Xi'an. ② They asked me things that happened before the boy was born. 8. 不少的语法书上说，before引导的从句习惯上不与否定的主句连用，要用until。
实际上二者都可以，有时在意义上有些区别。
试比较： He didn't arrive until I returned. 直到我回来时他才到达。
He did not arrive before I returned. 在我回来之前他尚未到达。
I didn't manage to do it until you had explained how. 直到你解释了如何干，我才设法完成了那项工作。
I didn't manage to do it before you had explained how. 你解释了如何干之后，我才设法完成了那件工作。
9. before在句中的含义比较灵活，虽然before引导的也是一个时间状语，但译成汉语时却不必死译为＂在……以前＂。
可以采取下面几种译法：（A）译为＂……才＂；（B）译为＂……就＂；（C）译为＂尚未＂、＂还没有＂、＂来不及＂、＂不要＂、＂别＂；（D）译为＂在……的时候还没有＂；（E）译为＂如果＂、＂否则＂、＂免得＂；（F）译为＂到＂、＂等到＂、＂没等……就＂；（G）译为＂然后＂等。
例如： A. It will be five years before we meet again. 要等五年我们才能再见面。
We waited a long time before the train arrived. 我们等了很长时间火车才到达。
B. I hadn't waited long before he came. 我没等多久他就来了。
He had not gone a mile before he felt tired. 还没走一英里路，他就觉得累了。
C. His father died before he was born. 他尚未出世他父亲就去世了。
Catch him before he escapes. 抓住他，别让他跑了。
Take this computer before you change your mind. 买了这台电脑，不要三心二意了。
D. We arrived there before it began to rain. 我们到达那里的时候还没下雨。
E. Go before I call the police. 走吧，否则我叫警察了。
I had better go now before it is too late. 我最好现在就走，免得太迟。
Pigs will fly before he'll be a scientist. 如果他当科学家，猪都会飞了。
F. The crops will die before the rain fall. 等到天下雨，庄稼早枯死了。
Before I could sit down, he offered me a cup of tea. 没等我坐下，他就给我端上一杯茶。
G. I shaved before I went to the party. 我刮了脸，然后去参加宴会。
求语法中关于before的用法
Before的用法： 一、 before用作连词 1. before用作连词时，意思是“在……之前；还没来得及 …… 就”。
例如： Before she could move, she heard a great noise, which grew to a terrible roar. 她还没来得及动弹，就听见有很响的声音，接着就成了可怕的隆隆轰鸣声。
Before I could say a word, she had stormed out of the room. 不等我说一句话，她就冲出了房间。
Don't count your chickens before they are hatched. 不要高兴得过早。
2. 用于It + be + 时间段 + before...句型中，意思是“在……之后才……”。
例如： It will be five years before I come back. 我五年后才能回来。
It was not long before the enemy was driven out of their country. 不久之后，敌人就被赶走了。
如果主句中用否定式，则表示“不多久……就”。
It won't be long before they understand each other. 他们不久就会互相了解的。
3. 还有“趁……（还没有）”之意。
例如： They are thinking of buying the house before the prices go up. 他们正在考虑趁房价未涨时把房子买下来。
Do it before you forget it. 趁早动手，以免忘了。
二、before用作介词 before用作介词时， 可以指时间“earlier than在……之前”，也可以指位置“in front of在……之前”。
例如： There is nothing that has not been bitter before being ripe. 凡事在成熟前，都是有苦味的。
Don't put the cart before the horse. 不要本末倒置。
He was brought before the judge. 他被带到法官面前。
三、before用作副词 before用作副词时，意思是“at an earlier time / in the past以前”。
例如： I've seen the film Titanic before. 我以前看过《泰坦尼克》这部电影。
I have never seen such beautiful flowers before. 我以前从未见过如此美丽的鲜花。
四、短语before long与long before的区别 before long是“很快，不久”的意思， 可以用于各种时态。
例如： Before long, he went to America. 不久，他就去了美国。
I hope to see you before long. 我希望不久后再见到你。
而 long before是“很久以前”的意思，一般用在过去时或过去完成时的句子里。
例如： She said she had read the novel long before. 她说她很久以前就读过这部小说。
That happened long before. 那件事发生在很久以前
before用法
1.表示“在……之前”。
说明两个时间或两个事件之间的先后关系。
1)They had got everything ready before I arrived.在我到达之前他们已经把一切都准备好了。
2)She didn't understand me before I explained it to'her.在我向她解释之前，她不理解我的意思。
3)The train had left before I arrived at the station.在我到达车站之前火车已开走了。
2.表示“……才…… ”，强调从句的谓语动词所表达的时间、距离很长或花费的力量比较大。
1)The workers worked long hours for two weeks before everything returned to normal.工人们长时间地工作了两周，一切才恢复 正常。
2)Thebig fire lasted four hours before the firemen brought it under contro1.大火持续了四个小时，消防队员才把它控制住。
3) We waited a long time before the train arrived.我们等了很长时间火车才到。
3.表示“还未来得及……就……”，强调主句谓语动词所表达的时间、距离很短或花费的精力比较小。
1)Before I could figure out what had happened,he forced me into the car.我还不知道发生了什么，他就强行把我推进了汽车。
2)He jumped into the water before I could stop him.我还没有来得及阻止他，他就跳进了水里。
3)Her father died before she was born.她尚未出世父亲就去世了。
4.表示“趁着……”。
1)We can set off early before it gets hot.我们可以趁着天不热早点出发。
2)You'd better write the phrases down before you forget them.趁着你还没有忘记，赶紧把这些词组写下来。
3)Please put them away before they are missing.趁着他们还没有丢，把它们收好吧。
5.表示“一……就”、“刚刚……就”。
与hardly.scarcely连用o 1)He hadhardly gone to bed before(=when)the door bell rang.他刚刚睡下，门铃就响了。
2.She had scarcely got off the train before(=when)her daughter ran towards her.她刚一下车，女儿就跑了过来。
6.表示“不知不觉多少时间已经过去了”。
1)He was so absorbed in his work that four hours had passed before he knew it.他如此专注于工作，不知不觉四个小时就过去了。
2)Time passed quickly and three months went by before he knew it.时间飞快地流逝，他没感觉到三个月已过去了。
7.表示“宁可。
宁愿”，相当于rather than。
1)I'd die before I apologized to＂them.我宁死也不向他们道歉。
2)1 would be poor before I got money in this way.我宁愿穷也不愿用这种方式挣钱。
8.before常用于句型“it was……before……”“ 过了（多长时间）才…… ”，“it will be……before…… ” “要用（多长时间）才……”。
“it wasn't……before……” “没过（多长时间）就……”。
“it won't be……before……”“用不了（多长时间）就会……”。
1)It was long before he came to help me.过了很久他才来帮我。
2)It wash't long before the fire was put out.不久火就给扑灭了。
3)It will be another five days before we finish this task.还要再过五天我们才能完成任务。
4)It won't be a long time before someone comes to see you.不久就会有人来看你。
before什么意思及同义词
1.ago表示“从现在起的若干时间以前”，意思是“距今……以前”，需和过去时或过去进行时连用。
before泛指“从过去起的若干时间以前”，意思是“距过去某时……以前”“与其……（毋宁）”，常和完成时连用，尤其在间接引语中，如：I visited him three days ago, but he had gone to Shanghai a week before.我三天前去访问他，但他已与那时的一周前到上海去了。
His parents died ten years ago.他父母十年前都去世了。
He said that his parents had died ten years before.他说他父母亲十年前都去世了。
I have never been there before.我以前从来没有去过那里。
2.如果不具体表明多少时间以前，只用before不用ago，意为“从前、以前”。
before仍以副词的形式置于被修饰语后，常与完成时候过去时连用。
如： Have you seen this film before? He asked me whether I had been to the Great Wall before. 3.表示在某一点时间或事件以前时，只用before不用ago，这种用法是将before当作介词或连词使用。
ago不具有这一功能。
如： They will come back before six o'clock. It is hoped that this will be finished before the year 1995.希望这件工作将在1995年以前完成。
另外，before在句中的含义较多。
不少句子中，before虽然引导的也是一个时间状语，但是译成汉语时却不必译为“在……以前”。
a.如果before引导的从句动作发生得晚或慢，可译成“……才”。
这是主句主语或是名词、代词，或用it作形式主语. He had almost knocked me down before he saw me.他几乎把我撞倒才看见我。
It will be hours before he arrives.要过几个钟头他才回到达。
You must sow before you can reap.有播种才能有收成。
b.如果强调从句动作发生之前，主句动作已发生，可译成“未……就”或“还没有……就”。
Before I could get in a word he had measured me.我还没有来得及插话，他就给我量号了尺寸。
Lu Ban built nine pavilions, but before he could finish the tenth, he heard a cock crowing.鲁班建了九个亭子，但他还没完成第十个就听到公鸡叫了起来。
c.有些句子中的before可译为“先……然后”、“先……再”。
Don't count the chickens before they are hatched. 不要乐观得太早。
Be pupil before you become a teacher.先做学生，再做先生。
有些句中的before还可译为“在……内”、“趁”、“没”。
They arrived before I expected.我没想到他们到得那么早。
Study hard before it is too late.趁早努力学习。
I had better go now before it is too late.最好我现在就走，免得太迟. I will be through this book before three days have passed.我要在三天内看完这几本书. before sb.knew it 一类习惯说法，常译为“不知不觉……就”、“还没弄清……就”、“不知怎么地……就”。
Time passed quickly and three months went by before Aqiao knew it.时间飞快的流失，阿巧不知不觉地在那里度过了三个月。
He fell from the tree before he knew it.他不知怎地一下就从树上掉了下来。
4.加强语气，表示“早已”的意思或使叙述显得更生动，ago也可以用于完成时。
如： I had thought that he had died at least twenty years ago.我本以为他至少二十年前就去世了。
In fact, I have long time ago known the secret.其实我早就知道那个秘密。
5.在表示对过去事情猜测的“情态动词+have+过去分词”或“动词的非谓语形式+have+过去分词”的结构中，ago也可以和完成时连用。
如： The building is said to have been destroyed in a fire two years ago.据说那栋大楼在两年前的一场大火中已被烧毁。
The incident must taken place years ago.这是一定发生在好几年以前。
You can not have met him a moment ago.刚才你不可能遇见他。
He may have left an hour ago.他可能在一小时以前就走了。
Having read the article a week ago, I know it very well.一个星期以前我已读过这篇文章，我很熟悉。
此外，before也可用于过去时，它和ago不同之处在于：before在句中单独使用，而ago必须和表示时间的词语连用。
如： I never saw him before.我以前从未见过他。
I saw him two days ago.我两天前见过他。
更详细的可以看 ；） http://www.jiangshuye.com/Article_Print.asp?ArticleID=1044
before和：before的区别
after介词 1.在...以后 After graduation he went abroad.毕业后他去了国外.At half after ten it began to rain.在十点半下起雨来.2.在...后面；随...之后 After you with the paper,please.请您看完报纸后给我.She entered the hall after her mother.她跟随在她母亲之后进入厅内.3.低于；次于 A captain comes after a major.上尉军衔低于少校.4.鉴于，由于 After what had happened he could not continue to work there.鉴于所发生的事情，他不可能继续在那里工作下去了.5.仿照，模仿 This is a painting after Picasso.这是一幅仿毕加索的画.6.依照；按照...的名字 The kid was named after his grandfather.这孩子是以他祖父的名字命名的.7.尽管 After all our efforts,the experiment failed.尽管我们做了努力，试验还是失败了.8.搜寻，寻找 Mary is after a better job.玛丽在寻找一个更好的工作.连词 1.在...之后 I will tell you after they leave.他们走后我再告诉你.副词 1.以后，之后 They arrived shortly after.不久以后他们抵达了.2.在后面，随后 Tom went on Monday,and Mary left the day after.汤姆星期一走的，玛丽第二天就离开了.形容词 1.以后的 His health was declining in after years.在以后的岁月，他的健康不断衰退.2.后部的 A few passengers would have a stroll on the after deck before the evening meal.几位乘客将在晚饭前到后甲板上散步.before介词 1.在...以前 Only two days remained before the examination.考前只剩下两天了.2.（指顺序、重要性等）在...之前，先于 Your name comes before mine.你的名字在我之前.Pride comes before a fall.骄必败.3.由...考虑中 We will put the matter before the committee.我将把此事提交委员会考虑.4.在...前面；在...面前 She said she had never spoken before an audience.她说她从未在大庭广众讲演过.副词 1.较早 Come at two o'clock,not before.两点钟来，不必再早了.2.以前；曾经 He was never late before.过去他从不迟到.Have you two met before？你们两人以前见过面吗？3.在前；向前 Several soldiers went before to scout.数名士兵在前面探路.连词 1.在...以前 Check it carefully before you hand it in.交来之前仔细核对一下.2.与其...宁可 I'd die before I'd tell.我宁死也决不会说出来.3.否则，要不然 Get out before I call the police.滚开，否则我叫警察.
before和until的区别及用法,要有例句
实际上，只要我们把握住两者使用时本身的含义及主句动词是终止性的，还是延续性的，肯定式，还是否定式两大点，就能容易地解决这类问题。
现详细阐明如下： 一、在下列情况下，两者可互换用，但含义略有不同。
before表示“在……之前”的意思，强 调时间先后关系；而until表示“直到……才”的意思，主句是肯定句则表示主句动作的终 止时间；主句是否定句则强调主句动作的起始时间。
1.主句为否定式终止性谓语动词。
常见的动词是open,start,leave,arrive,finish, stop等。
例如： （1）The noise of the street didn't stop until/before it was midnight. (2)The children won't come back until/before it is dark. (3)I didn't leave the lovely boy until/before his mother came home. 2.主句为肯定式、延续性谓语词，这类动词用stand,stay,talk,be,wait等。
例如： （1）He lived with his parents until/before he graduated from school. (2)I will wait until/before he comes to my help. (3)I shall stay heer until/before you come back. 二、在下列情况下，用before不用until。
1.主句这肯定式、终止性谓语动词，只用before。
例： （1）He fell asleep before I could take off his clothes. (2)We arrived there before it atarted to rain. (3)The holiday came to the end befor I knew it. (4)He almost knocked me down before he saw me. 2.主句谓语动词强调动词的迟缓性，只用before，常伴有时间段状语或时间段暗示。
例： （1）It was quite some time before he found the elephant at all. (2)We had walked a long way before we found some water. (3)We had sailed for two days before we saw the land. (4)The fire lasted about four hours before the firefighters could countrol it. (5)It was midnight before my brother came home. (6)It was three months before they met again. 3.如果强调从句谓语动作未发生，就发生主句谓语动作，只用before。
常译为“未及”，“不”或“不等……就”。
例： （1）We can leave early in the morning before it gets too hot. (2)I must write it down before I forget it. (3)We do want to buy something now before prices go up. 4.表“与其说……倒不如”，“与其……毋宁……”只用before。
例： （1）I would give up my job before I'd agree to be dismissed. (2)He will die of hunger before he will steal. 5.在某些特定句型中用before。
例如： （1）It was not long before the whole country rose up. (2)It will probably not be long before they understand each other. 三、下列情况一般区别用until。
1.主句是持续性谓语动词时，肯定、否定都可以，但意义完全不同。
肯定表动作终止，而否定表动作开始。
例如： （1）We discussed the problem until/before he came back.我们一直讨论到他回 来。
（2）We didn't discuss the problem until he came back.我们一直等到他回来后才讨论问题。
2.not…until句型尽管在某些情况下可与before互换用，但在强调句中一般仍用until。
例如： （1）It was not until he told me that I knew it. (2)It was not until he finished his homework that he went home.
