什么是英语条件句?具体?分类?

条件句的表达形式有：
1. if如果
You should call 119 if there's a fire.
If you think that treating a woman well means always getting her permission for things, think again. (06湖南)
2. unless如果不,除非(多数情况下与if...not用法相同,两者都引导条件状语从句,但unless比if ... not的语气要强｡
例如：
You will be late , you leave immediately.
A. unless B. until C. if D. or
答案A｡句意： 除非你立即走,否则你会迟到的｡该句可转化为If you don’t leave immediately, you will be late. B､D项填入后句意不对,or表转折,若用or则句子应为： Leave immediately or you will be late. 再如：
He is sure to come unless高考资源网 he has some urgent business. = He is sure to come if he hasn’t any urgent business.
注意： 当unless引导的从句的主语与主句的主语相同时,unless后面的主语和动词有时可省略｡
Unless (he is) in uniform, he doesn’t look like a policeman.除非他穿着制服,否则他看起来不像警察｡
He will not come unless (he is) invited.除非被邀请,否则他是不会来的｡
但在下列情况下要斟酌替换使用：
1) 当从句是虚拟形式时,只用if ... not,不用unless引导｡例如：
The flowers would have died if you had not watered diligently.
2) 当主句为疑问句时,不用unless,而用if ... not｡例如：
What shall we do if he doesn’t reply to our letter?
3) 当unless引导的从句带有否定词时,不能用if ... not代替｡例如：
I’ll go unless no one else goes.
3. as long as只要
As long as there is life there is hope. 有生命就有希望｡(留得青山在,不怕没柴烧｡)
I’ll accept any job as / so long as I don’t have to get up early.只要不必早起,任何工作我都可以接受｡
4. once作连词表示“一旦,只要”,引导条件状语从句｡
Once you understand the rules of the game, you will enjoy it.一旦你了解了游戏的规则,你就会喜欢它｡
Once he is free, he will play computer games. 只要他有空,他就玩电脑游戏｡
例如：_______environmental damage is done, it takes many years for the ecosystem(生态系统) torecover.
A. Even if B. If only
C. While D. Once
解析： 答案为D｡even if“即使”,if only “要是……就好了”,while“虽然”, once“一旦”｡句意为“一旦环境遭到破坏,就要花很多年才能恢复生态系统”,故D正确｡once作连词表示“一旦,只要”,引导条件状语从句｡再如：
5. 祈使句或名词短语 + 含有一般将来时或情态动词的陈述句
例如：Dress warmly, you’ll catch cold.
〔A〕 on the contrary 〔B〕 or rather 〔C〕 or else 〔D〕 in no way
〔分析〕 本题考查固定句型：“祈使句+or (else) /and you will...”.其中,祈使句相当于if或unless引导的条件状语从句,并列连词后面的句子多用将来时表示结果.连词or (else)（也可以用otherwise）意为“否则”,后面的句子是转折的结果；连词and意为“那么,如此一来”,后面的句子是顺承的结果.如：Wait a minute and I’ll tell you all about it.（再等一会儿我就会告诉你事情的全部.）Come on, or you will miss the chance.（加油,否则你将失去这个机会.）本题中前后分句是转折关系,应选〔C〕or else.
其他选项都是固定短语,但是表示的逻辑关系均不符合句意.on the contrary意为“（与此）相反”,如：I thought the movie would have been terrible; on the contrary it is very interesting.（我原以为这部电影会很糟糕,结果相反,它很有意思.）or rather意为“更确切地说”,如：I am 1 year older than you, or rather 1 year and 2 months.（我比你大一岁,更确切地说大一岁零两个月.）in no way意为“决不”,放在句首时,引起句子倒装,如：In no way can we allow this to continue.（我们决不允许它再继续下去.）
〔句意〕 穿暖和一些,不然你会感冒的.
6. provided意为“如果,倘若,只要”,引导条件状语从句
You can arrive in Beijing earlier for the meeting you don’t mind taking the night train.
〔A〕 provided 〔B〕 unless 〔C〕 though 〔D〕 until
〔分析〕 provided意为“如果,倘若,只要”,引导条件状语从句,相当于if,如：The boss will pay the bonus provided（that）the job is completed on time.（如果工作按时完成的话老板将发奖金.）unless相当于if …not,引导条件状语从句,意为“如果……不……,非…… 不可,除非”,由于它是具有否定意义的连接词,因此所引导的从句谓语一般是肯定形式,如：Unless the rain stops,I shall not go out for a walk.（倘若雨不停,我就不出去散步了.）though意为“虽然,尽管；可是,然而”,引导让步或转折从句,如：Though she gave no sign, I was sure she had seen me.（尽管她没有示意,我还是确信她看见了我.）Your suggestion is feasible, though it may be rather costly.（你的建议是可行的,但也许要付出不少代价.）until常和not搭配,引导时间状语从句,意为“直到……才”,如：He did not leave the house until his father returned.（他直到父亲回来才离开房子.）根据句意,应选〔A〕provided.
〔句意〕 假如你不介意乘夜班车的话,你就可以早点儿到达北京开会
,: 150%; FONT-FAMILY: 'Times New Roman'; mso-bidi-font-size: 10.5pt">”,引导条件状语从句You can arrive in Beijing earlier for the meeting you don’t mind taking the night train.
〔A〕 provided 〔B〕 unless 〔C〕 though 〔D〕 until
〔分析〕 provided意为“如果,倘若,只要”,引导条件状语从句,相当于if,如：The boss will pay the bonus provided（that）the job is completed on time.（如果工作按时完成的话老板将发奖金.）unless相当于if …not,引导条件状语从句,意为“如果……不……,非…… 不可,除非”,由于它是具有否定意义的连接词,因此所引导的从句谓语一般是肯定形式,如：Unless the rain stops,I shall not go out for a walk.（倘若雨不停,我就不出去散步了.）though意为“虽然,尽管；可是,然而”,引导让步或转折从句,如：Though she gave no sign, I was sure she had seen me.（尽管她没有示意,我还是确信她看见了我.）Your suggestion is feasible, though it may be rather costly.（你的建议是可行的,但也许要付出不少代价.）until常和not搭配,引导时间状语从句,意为“直到……才”,如：He did not leave the house until his father returned.（他直到父亲回来才离开房子.）根据句意,应选〔A〕provided.
〔句意〕 假如你不介意乘夜班车的话,你就可以早点儿到达北京开会