条件情况 作用 例 句
一、当条件句表达无限制真实情况，主句也是一种无限制结果。这样的条件句前后都用事实句，不用特殊动词。
1.无限必然Oil floats if you pour it on water. If you spill water on the floor,it runs all over the place.
2.习惯经常He usually gets angry if we say anything about his accent.
My dog always barks if he hears any strange sounds.
Mr Wood seldom drives to work if the weather is bad.
3.客观事实If you eat slowly you digest your food better. If you eat bad plums, you get ill.
If I am happy, I smile. If I am sad, I cry. If a baby is hungry,it cries.
4.引申主句If you are right, I am wrong.
If you win, I lose.
If you have been travelling all night,you probably need a rest.
5.附加解说If there is anything I wanna do now,it is to take a rest.
If you wanna know the contents of the book,I haven't read it.
If yoy like to watch football,Liverpool will be playing against Aberdeen.
If you are going out,it's raining.
二、当条件句表达人为认定将要发生的事情为真实情况，主句为预料判断结果。这样的条件句用事实句，结果句可用特殊动词will/shall/can/may/must/ought/be+不定式构成。
1.主观预料I won't get lost if I take the map.
If you don't hurry up,you will be late.
If you don't concentrate on your studies,you won't pass the exam.
If you don't hurry and get there before 5,he will have left the office.
2.猜测 If you eat these bad plums,you may get ill.
If he doesn't work hard,he might fail.
3.表责备 If he has an exam tomorrow,he ought to have an early night.
4.表能力 If you come to Beijing next month,we can put you up.
5.表计划 If we go to the beach tomorrow,we are taking a picnic lunch.
What are we to do if it rains ?
6.表推测 If he isn't careful,he is going to have an accident.
7.即将发生 If you do it,you will be breaking the law.
8.表建议 If you get lost in the city,don't hesitate to ask a policeman.
If you require information on trains, wait here.
If your dog starts barking,take it out for a walk.
三、有时条件句也可以使用完成时态、进行时态及各种情感时态。
1.表推断 If my car is working this afternoon,I can take you to the station.
2.表打算 If you are going to see a film,don't forget to book a ticket.
3.表邀请 If you can come with me to the party,I'll have a much better time.
4.表无奈 If I have to go to my lawyer about this problem,it will cost me a lot.
5.表必要 If you must go to a doctor,please choose a good one.
6.表愿意 If you will return the sample enclosed in this letter,we shall be greatful.
If the bank manager would grant me a loan,I would buy that house.
I'll ring up his secretary,if you would prefer to make a later appointment.
7.表责任 If he has finished his work by six o'clock,we shall be able to take him with us.
四、为表示说话人不肯定语气，if从句可一律使用should,主句用特殊动词。主句若再用特殊动词委婉式，则语气更加婉转,可视为虚拟。此情况可倒装。表不确定万一 If the money shouldn't arrive,how will we pay the rent ?
If she should fail,she can try again.
If you should be late,you must apologize to your boss.
Should you see Helen at the conference,tell her I'm here.
If you should be passing my house,you might return the book you borrowed.
If he should come tomorrow,I would tell him everything.
If you should like to meet her,I could ring her up.
If you should help me,I would feel much obliged.
Should he come tomorrow,I would tell him everything.
Should she fail,she can try again.
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