if从句主句用法

IF;某事很可能发生，条件是可能存在的，主句中某种情况发生的概率也是很高的。如： If you ask him，he will help you．如果你请他帮忙，他会帮你的。 If you fail in the exam，you will let him down．如果你考试不及格，你会让他失望的。 If you have finished the homework， you can go home．如果你作业做完了就可以回家了。 另外，if从句还表示不可实现的条件或根本不可能存在的条件，也就是一种虚拟的条件或假设。从句多用一般过去时或过去完成时，表示对现在或过去的一种假设。如： If I were you，I would invite him to the party．如果我是你，我会邀请他参加聚会。 I would have arrived much earlier if I had not been caught in the traffic．要不是交通堵塞，我本会来得早一些。 另外你还要注意if 条件句的时态搭配 1．if从句用一般现在时，主句用一般将来时 If he runs he’ll get there in time. 如果他用跑的，他就会及时赶到那儿。 The cat will scratch you if you pull her tail. 如果你拉猫的尾巴，它就会抓你。 2．if从句用一般现在时，主句用may/might/can If the fog gets thicker the plane may/might be diverted. 如果雾在大一些，飞机可能就会改在别的机场降落。 If it stops snowing we can go out. 如果雪停了，我们就可以出去。 3．if从句用一般现在时，主句用must/should If you want to lose weight you must/should eat less bread. 如果你想减肥，你必须少吃面包。 4．if从句用一般现在时，主句用一般现在时 If you heat ice it turns to water. (也可用will turn)如果把冰加热，它就会化成水。 5．if从句用现在进行时，主句用一般将来时 If you are looking for Peter you’ll find him upstairs. 如果你是在找彼得，上楼就会找到他。 6．if从句用现在完成时，主句用一般将来时 If you have finished dinner I’ll ask the waiter for the bill. 如果你吃完了，我就叫服务生来算账 那么,除了if之外,是否还有其他连词也可以引导条件状语从句呢?回答是肯定的,不仅有,还有很多。这些词由于出现的频率较小,且用法较复杂一些,所以不如if为大家所熟知罢了。下面就这些词的用法以例句的形式进行一下简单总结。   1. unless conj.除非,若不,除非在……的时候   You will fail to arrive there in time unless you start earlier.如果你不早点动身,你就不能及时赶到那儿。   Unless it rains, the game will be played.除非下雨,比赛将照常进行。   2. on condition(that)...在……条件下,如果   on condition (that)...引导的条件从句是主句事件发生的前提条件或唯一条件。   I can tell you the truth on condition that you promise to keep a secret.我可以告诉你真相,条件是你答应保守秘密。   You can go swimming on condition (that) you don't go too far from the river bank.你只有在不远离河岸的条件下才可以下水游泳。   3. supposing conj.如果,假如   supposing引导的条件从句表示一种假设条件。   Supposing it rains, shall we continue the sports meeting?倘若下雨,我们的运动会还要继续举行吗?   Supposing something should go wrong, what would you do then?假如出了什么问 题 快递公司问题件快递公司问题件货款处理关于圆的周长面积重点题型关于解方程组的题及答案关于南海问题 ,你准备怎么对付?   4. provided conj.假如,除非,以……为条件   provided (that) +从句表示一种假设条件。   He will sign the contract provided we offer more favorable terms.如果我们提出更优惠的条件,他就会在合同上签字。   He won't be against us in the meeting provided that we ask for his advice in advance.如果我们提前征求一下他的意见,他就不会在会上反对我们。   从上述例句可以看出if, unless, on condition (that), supposing, provided等词引导的条件状语从句,主从句条件关系分明,结构清晰。但有些句子,虽没有含条件关系的连词,却也隐含着条件关系,这些句子常用一些词,如but for, without等引出一个介词结构来表示条件,条件常常是虚拟的,或与事实相反的假设。如:   but for若非,要不是   But for the rain, we should have a pleasant journey.要不是下雨,我们的旅行肯定会很愉快。   But for your help,we should not have finished in time.要不是你帮忙,我们肯定不能及时完成任务。 重点2  -if句 上个学期，我们曾经学过由if 引导的句子，你还记得吗？对了，“ I’ll not go to the zoo if it rains tomorrow. ( 假如明天下雨，我就不去动物园。) You can come to the party if you don’t wear jeans.（ 如果你不穿牛仔裤，你就能来舞会。）” 这个学期又在本单元见到了似曾相识的同样由if引导的句子，比如：“If I won the lottery, I would give it to medical research. （ 假如我赢了彩票的话，我就捐给医学研究。） If I were you, I would wear jeans and T-shirt.（ 如果我是你，我就穿牛仔裤和T恤。）” 这两个单元学到的句子都是由if引导的。那么，它们有什么区别呢？ 分两种情况： 1．something may possible happen 某事发生的可能性较大。 这种情况，有个十三字口诀：“主将从现，主过将从过，主现从现”。即主句是一般将来时，从句用一般现在时；主句用过去将来时，从句用一般过去时；当主句中有can/can’t的话，则从句用一般现在时。例如： If he has time, he will come tomorrow. If she finishes early, she can come back early. If you don’t do homework, the teacher will scold you. Ⅰ.单项选择（15分） 1.If you _____ to the party, you’ll have a great time. A. will go  B. went  C. go  D. going 2. It will be a long time ____ Peter _____ his work. A. since, has finished  B. after, finishes  C. when, will finish  D. before, finishes. 3. What will father _____ us from Japan? A. take  B. bring  C. carry  D. make 4. Weifang is famous ______ kites. A. for  B. to  C. on  D. with 5． I ____ her the answer if she ____me. A. can tell, will ask  B. will tell, will ask  C. would tell, ask  D. will tell, asks 6. – What are you going to do tomorrow?   --We’ll go to the library tomorrow if it ____. A. isn’t rain  B. rain  C. won’t rain  D. doesn’t rain 7.—Do you know when he will come back tomorrow? --Sorry, I don’t know. When he ____ back, I’ll tell you. A. comes  B. will come  C. come  D. may come 8. What will you do if you _____ to the old folk’s home visit? A. go  B. went  C.going  D. will go 9. If I eat ____ food, I’ll be very fat. A. too many  B. many too  C. too much  D. much too 10. I’ll give the book to him if he ___ here next Sunday. A. will come  B. comes  C. is coming    D. came 11. There ____an English film in our school tomorrow. A. is going to have  B. will have  C. is going to be  D. has 12. Could you tell us where ____？ A. will the next Olympic Games held  B. the next Olympic Games will be held C. would the next Olympic Games be held D. the next Olympic Games would be held 13. When my mother returned last night, I ____  a book. A. read  B. am reading  C. was reading  D. am going to read 14.What ____ you ____ when it began to rain? A. do, do  B. were, doing  C. are, doing  D. did, do 15. I’ll wake you up when he ____back. A. will  B. is going to come  C. comes D. come 1---5 CDBAD    6---10 DAACB  11---15 CBCBC I.选择最佳答案. (  ) 1.If it ______ sunny tomorrow, I ____ boating.                  a. is go      b. will be, go  c. is, will go  d. will be, will go (  ) 2.----what will you do if it ______ tomorrow,       ----I’ll stay at home and watch TV.     a. rain      b. rains    c. will rain    d. is raining II. 同义句转换 1. Run fast, or you’ll be late for school.   _______ you _______ _______ fast, you’ll be late for school. 2. You can buy the dictionary if you take enough money with you. Take enough money with you, ______ _____ ______ buy the dictionary. 3. If there is no air, none of us can live.   None of us can live _______ _________. 请将下列句子翻译成英语。 1. 如果明天有空，我和你一起参观十三陵。 _______________________________________________ 2. 如果我们骑自行车去上班，我们可以避免空气污染。 ______________________________________________ 3. 如果你去青海湖，你将能看到青海湖自行车比赛。 _______________________________________________ 4. 如果明天他不来,我会代替他去的。 _______________________________________________ .选择最佳答案. ( c ) 1.If it ______ sunny tomorrow, I ____ boating. a. is go b. will be, go c. is, will go d. will be, will go ( b ) 2.----what will you do if it ______ tomorrow, ----I’ll stay at home and watch TV. a. rain b. rains c. will rain d. is raining II. 同义句转换 1. Run fast, or you’ll be late for school. If you don't run fast, you’ll be late for school. 2. You can buy the dictionary if you take enough money with you. Take enough money with you, and you can buy the dictionary. 3. If there is no air, none of us can live. None of us can live without air. 请将下列句子翻译成英语。 1. 如果明天有空，我和你一起参观十三陵。 If I am free tomorrow,I will go to the Shisan mausoleum with you. 2. 如果我们骑自行车去上班，我们可以避免空气污染。 If we go to work by bike,we can prevent the air from polluting. 3. 如果你去青海湖，你将能看到青海湖自行车比赛。 If you go to the Qinhai Lake,you can see the Qinhai Lake bicycle match. 4. 如果明天他不来,我会代替他去的。 If he doesn't come tomorrow,I will go instead of him.