英国前首相撒切尔夫人（Margaret Thatcher）曾用if条件句对男人和女人进行评价：
In politics, if you want someone to make a speech, ask a man; if you want something done, ask a woman. 在政治领域，如果你想要有人发表演说，那就找男士去；而如果你想真正把事情解决，那就找女士。
一、概念
连词if的意思是“如果”，它引导的句子表示某事发生所需要的条件，即“在……条件下某事才能发生”，在句子中充当状语，因此我们称之为条件状语从句。在复合句中连词if引导的句子为从句，被修饰的句子为主句。从句可以放在主句后，也可以放在主句前，从句放在主句前时，应用逗号将它与主句隔开。例如：
We’ll go to the Great Wall if it doesn’t rain tomorrow. = If it doesn’t rain tomorrow, we’ll go to the Great Wall. 如果明天不下雨，我们就去长城。
二、用法
1. 条件状语从句通常由连词if引导，意为“如果，假如”，主句不能用be going to 表示将来，而应该用shall或will。例如：
If I’m free tomorrow, I’ll go with you. 如果我明天有空，我将会和你一起去。
2. if引导的条件状语从句，主句用一般将来时，从句则用一般现在时，即“主将从现”。例如：
If it is sunny tomorrow, I’ll climb the hill. 如果明天天气晴朗，我将去爬山。
3. 正确区分if引导的条件状语从句和if引导的宾语从句。
在条件状语从句中，if表示“如果”；而在宾语从句中，if表示“是否”。可以用下面的方法区分：
1) 从句前置法：if引导的条件状语从句，可以放在主句之前并用逗号隔开，也可放在主句之后；而if引导的宾语从句只能放在主句之后。因此如果把if放在主句之前，句子通顺，意义不变，则是条件从句，否则是宾语从句。例如：
He will help you if you ask him. = If you ask him, he will help you.
如果你问他，他会帮助你。
2) whether替换法：if引导宾语从句时，其意为“是否”，通常可用whether替换，意义不变，而if引导条件状语从句时不能用whether替换。因此，可用whether替换的是宾语从句，不能替换的是条件从句。例如：
I want to know if you will go tomorrow. = I want to know whether you will go tomorrow.
我想知道你明天是否去。
注意：区分if的用法有着极为重要的意义，因为在条件状语从句中，主句用将来时，从句用一般现在时；而在宾语从句中，当主句是一般现在时，从句可用所需的任何时态，主句是一般过去时，从句用过去的某种时态。
一、单项选择
1. If you _____ to the party, you’ll have a great time.
A. will go
B. went
C. go
D. going
2. 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
3. — 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
4. — 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
5. I’ll give the book to him if he ____________ here next Sunday.
A. will come
B. comes
C. is coming
D. came
6. There ____________ an English film in our school tomorrow.
A. is going to have
B. will have
C. is going to be
D. has
7. I’ll wake you up when he ____________back.
A. will
B. is going to come
C. comes
D. come
8. The football match will be put off if it ________.
A. will rain
B. rains
C. rained
D. is rained
9. There ________ a basketball game this afternoon.
A. is going to have
B. will be
C. is going to play
D. will play
10. I won’t go if it ________ tomorrow.
A．rain
B．is raining
C．rains
D．will rain
二、用所给词的适当形式填空
1. If you ________(feel) tired, you _________ (have) to have a rest.
2. Where ________ he ________ (see) the film if he _________(have) time?
3. If there ________ (be) fewer trees, there ________ (be) more pollution.
4. He ________ (dress) more casually if he ________ (not work) on weekends.
5. If Marcia ________ (live) alone, she ________ (keep) a pet parrot.
6. Lana ________ (buy) a new dress if the old one ________ (be) out of style.
7. The twins ________ (fight) if they________ (argue).
8. I ________ (have) a bake sale if I ________ (need) money for education.
9. Peter ________ (send) me a beautiful souvenir if he ________ (go) to Spain.
10. If Mr. Green ________ (say) I am hard- working, my parents ________ (feel) glad.
11. I ________ (go) to the beach if it ________ (not rain) this week.
12. ________they ________ (have) a match if the P.E. teacher________ (be) not busy?
13. He ________ (write) a letter to his grandparents if he ________ (get) his report card this week.
14. If she ________ (get) up late, she ________ (not catch) the early bus.
15. Peter ________ (major) in English if he ________ (pass) the exams in Peking University.
三、完成句子
1.如果他迟到了，会发生什么事情？
What _______ ________ if he _______ late?
2. 如果努力学习，你就会取得好成绩。
If you_______ _______, you _______ _______ good _______.
3. 他如果看电视太久了，他的父母会不高兴。
If he _______ TV too much, his parents _______ _______ unhappy.
4. 如果我们为他举办生日聚会，大家都会来的。
Everyone _______ _______ if we _______a birthday party _______ him.
5. 如果明天不下雨，我会和你一起去公园的。
If it _______ _______ tomorrow, I _______ go to the park _______ you.
6. 如果她睡过头了，就会误了开会的。
She _______ _______ _______ _______ the meeting if she _______ _______.
7. 如果他有空，他会帮助你的。
If he _______ _______, he _______ _______ you.
8. 如果Tom考试不及格，他就没有机会上高中了。
Tom _______ miss the chance to go to the high school if he _______ the exams.
9. 你如果抄同学的作业就不能学好各门功课。
You _______ _______ good at all the subjects if you _______ the other students’ homework.
参考答案
一、单项选择。
1. C。本题是if引导的条件状语从句，主句用一般将来时，从句用一般现在时，即“主将从现”，所以答案为C。
2. D。根据句意“如果她问我，我就告诉她答案。”可知本句是if引导的条件状语从句，主句用一般将来时，从句用一般现在时，从句的主语为单三，动词后加-s，所以答案为D。
3. D。条件状语从句，主句用一般将来时，从句用一般现在时，rain在此是实义动词“下雨”的意思，故答案为D。
4. A。根据“主将从现”可知本句答案为A。此题是when引导的时间状语从句。
5. B。根据“主将从现”可知答案为B。
6. C。be going to do，will do都可以表示将来的动作，但只有选项C符合There be句型要求。
7. C。根据“主将从现”可知答案为C。
8. B。根据“主将从现”可知答案为B。
9. B。本题考查there be句型的一般将来时，there will be，故答案为B。
10. C。根据“主将从现”可知答案为C。
二、用所给词的适当形式填空
1. feel; will have
2. will; see; has
3. are; will be
4. will dress; doesn’t work
5. lives; will keep
6. will buy; is
7. will fight; argue
8. will have; need
9. will send; goes
10. says; will feel
11. will go; doesn’t rain
12. Will; have; is
13. will write; gets
14. gets; won’t catch
15. will major; passes
三、完成句子
1. will happen; is
2. study hard; will get; grades
3. watches; will be
4. will come; have; for
5. doesn’t rain; will; with
6. will be late for; sleeps late
7. has time; will help
8. will; fails 9. won’t be; copy
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