一、条件状语从句用法 1、引导条件状语从句最常用的连词是if,由if引导的条件状语从句表示在某种条件下某事很可能发生。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。
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。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。
2、unless if...not. 除非,若不,除非在的时候 例如Lets go out for a walk unless you are too tired. If you are not too tired, lets go out for a walk. Unless it rains, the game will be played. 除非下雨,比赛将照常进行。
二、时态问题 在条件状语从句中，要注意“主将从现”的规定，即主句用一般将来时，从句用一般现在时表示将来时。例句 I will come to see you if I have time. 我有时间，我就来看你。
三 如果 if 条件句谈论的是重复发生和预示要发生的情景和事件，则主从句大多用一般现在时态。如 If bears are in danger ,they attack people. 误区提醒 if 既可以引导条件状语从句，表示“如果”，也可以引导宾语从句，表达“是否”。辨别它在这两种从句中的时态是我们经常容易出错的地方。另外，if 和unless的用法也需注意。
典型例题 ----I wonder if your wife to the party. ----If your wife _________, so will mine。. A. will go， go B. will go, goes C.goes, will go D. will go, will go 解析第一句中if表示“是否”，引导宾语从句，用将来时will go；
第二句“如果你的妻子去，我的妻子也去”，if引导条件状语从句，用一般现在时表示将来时。
your wife，单三人称主语，所以用goes 。
总结 IF引导的 一、表示将来可能发生的 1 If sb does sth, sb will do sth sb will do sth if sb does sth 主句一般将来时 从句一般现在时 2主句为祈使句或情态动词形式 If sb does sth, please do sth If sb does sth, sb may情态动词 do sth 二、表必然发生的 If sb does sth, sb/sth does sth sb/sth do sth if sb does sth 主句一般现在时， 从句一般现在时（相当于when引导的从句） Unless引导的 sb will do sth unless sb does sth if sb does not do sth 练习 1.He ______ fail in the exam if he ______ not study hard. 2.Unless you ______ leave now, you ______be late. 3.We ______ have a barbecue unless it ______ rain . 4.Hurry up, or you will miss the bus.（同义句转换） ___ you don’t hurry up, you ____ catch the early bus. 5.Study hard, or you’ll miss fall behind. （同义句转换） ______ you study hard, you______ fall behind. 6.If you don’t put on your scarf, you’ll catch cold. （同义句转换） Put on your scarf, _____ you’ll catch cold. 7.I don’t know if it_______ tomorrow. ）表是否，用将来时态 If it ____ ,I won’t go shopping. rain （表如果，用现在时态） 8.I want to know if he _________come tomorrow, if he _______come, I __________give the massage to him. 9. Please let us know if he ________arrive tomorrow. 请告诉我们他明天是否会来 Please let us know if he _________ arrive tomorrow. 如果他明天来的话请告诉我们 10.I’m sure if he _____go to the party, he________ have a great time. 11.If the rain _______stop tonight, we will go to the cinema. 12.I’ll buy a computer if I ______have enough money. 13.You _________not get nervous if you _____do enough rcise. 14.If she ____ be kind to me , I __________not argue with her. 15.If you _____pay more attention to that, he _________ not get injured. 16.Mr Li will be mad if we _______break the rules. 17. If it _____ be cloudy, they _______not go there by air. 18.Shall I say “Hello” when the foreigner ______come into the classroom 19.He’ll get better grades if he _________ study hard. 20. If you work really hard, you _______ be famous and rich. if 条件状语从句的时态练习 一．在正确的答案下划一条线。
1.Daina will go/go/goes to Europe if she will pass/pass/passes the exams . 2. The graduates will teach/teach/teaches in the poor village if the Ministry of Education will agree/ agree/agrees soon. 3. If a UFO will land/land/lands in front of me, I will go/go/goes in to look for the alien. 4. If he will have/have/has money, he will bulid/build/builds a science lab. 5.Don’t wait for me if I am/ will be late. 6.They won’t/don’t go to the beach if it will rain/rain /rains. 7. I will call/ call you if he will stay/stay /stays at home. 8. Will / Do/ Does he visit the museum if he won’t / don’t/ doesn’t get tired 9. Where will/ do/does they live if they will miss/ miss/ misses the bus 二、用所给词的适当形式填空 1.If you ________feel tired, you _______________ have to have a rest. 3. If there __________be fewer trees, there _______________ be more pollution. 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 ________________tour Spain. 10. If Mr Green ___________say I am hard- working, my parents