if引导的条件状语从句
（一）定义
if引导的句子在复合句中表示条件，假如if从句的动作发生，主句的动作就（不）会发生，因此称为条件状语从句。
（二）位置
if 引导的条件状语从句位置灵活，可直接放在主句后面，也可以放在句首。
放在句首时，从句后面要用逗号和主句隔开。
① If I have enough money, I will travel around the world.
② I will travel around the world if I have enough money.
（三）用法
① Work hard, and you’ll pass the exam easily. 努力学习，你将很容易通过考试。
→If you work hard, you’ll pass the exam easily.
② Hurry up, or you’ll miss the train. 快点儿，否则你就赶不上火车了。
→If you don’t hurry up, you’ll miss the train.
（3）当主句含有情态动词时，if引导的条件状语从句通常用一般现在时。
We must study hard if we want to pass the final exam.
如果想通过期末考试，我们必须努力学习。
（4）用含介词with或without的介词短语转换。
① If you help me, I'll finish my job soon.
→With your help, I'll finish my job soon. 如果你帮我，我将很快完成我的工作。
② If there is no water, fish can’t live.
→ Fish can’t l ive without water. 离开水，鱼不能生存。
（四）if引导的条件状语从句与if引导的宾语从句的区别
if引导宾语从句时表示“是否”，位于及物动词之后；
if引导的条件状语从句时表示“假如，如果”，位于句首或句中。
①I don't know if he will come tomorrow.
②If he comes, I'll call you.
练习
一、选择题
1. _____ you don't go to bed earlier, you will feel tired in the morning.
A. Unless
B. If
C. Though
D. Until
2. Why not look up the new word in a dictionary _____ you don't know it?
A. if
B. that
C. though
D. whether
3. Talk to your teacher and you will get help _____ you have a problem.
A. unless
B. if.
C. until
D. so
4. I won't go to tomorrow's party _____ I'm invited.
A. if
B. unless
C. when
5. The children will climb the hill if it _____ tomorrow.
A. won't rain
B.didn't rain
C. isn't raining
D. doesn't rain
6. We wonder if our teachers _____ to our graduating party next weekend. If they_____, we'll be very happy.
A. will come; will come
B. come; will come
C. will come; come
D. come; come
二、翻译句子。
1. 如果明天下雨，我们将在家看电视。
We'll stay at home watching TV if it _____ （rain）tomorrow.
2. 如果她早点起床，就有时间在家里吃早餐.
If she ______ _______ a little earlier, she ‘ll have time to eat breakfast at home.
3. 如果你参加聚会，你将会过得很开心。
If you ______ the party, you ______ ______ a great time.
4. 如果你经常听英文歌，你将会喜欢英语。
If you often ______ ______ English songs, you ______ _______ English.
一、BABBDC
二、1. rains 2. gets up 3. join, will have 4. listen to, will like。