条件状语从句
连接词主要有 if,unless,as/so long as,on condition that 等..
if 引导的条件句有真实条件句和非真实条件句两种.非真实条件句已在虚拟语气中阐述.
unless = if not.
Let's go out for a walk unless you are too tired.
If you are not too tied,let's go out for a walk.
典型例题
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,否则你就回迟到的.可转化为 If you dong leave immediately,you will be late.B、D句意不对,or表转折,句子如为 You leave immediately or you will be late.
我们知道,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.
I would have arrived much earlier if I had not been caught in the traffic.如果没有堵车,我会到的早一点儿.
那么,除了if之外,是否还有其他连词也可以引导条件状语从句呢?回答是肯定的,不仅有,还有很多.这些词由于出现的频率较小,且用法较复杂一些,所以不如if为大家所熟知罢了.下面就这些词的用法以例句的形式进行一下简单总结.
1.unless conj.除非,若不,除非在……的时候
You will fail to arrive there in time unless you start earlier.如果你不早点动身,你就不能及时赶到那儿.
Unless it rains,the game will be played.除非下雨,比赛将照常进行.
2.on condition(that)...在……条件下,如果
on condition (that)...引导的条件从句是主句事件发生的前提条件或唯一条件.
I can tell you the truth on condition that you promise to keep a secret.我可以告诉你真相,条件是你答应保守秘密.
You can go swimming on condition (that) you don't go too far from the river bank.你只有在不远离河岸的条件下才可以下水游泳.
3.supposing conj.如果,假如
supposing引导的条件从句表示一种假设条件.
Supposing it rains,shall we continue the sports meeting?倘若下雨,我们的运动会还要继续举行吗?
Supposing something should go wrong,what would you do then?假如出了什么问题,你准备怎么对付?
4.provided conj.假如,除非,以……为条件
provided (that) +从句表示一种假设条件.
He will sign the contract provided we offer more favorable terms.如果我们提出更优惠的条件,他就会在合同上签字.
He won't be against us in the meeting provided that we ask for his advice in advance.如果我们提前征求一下他的意见,他就不会在会上反对我们.
从上述例句可以看出if,unless,on condition (that),supposing,provided等词引导的条件状语从句,主从句条件关系分明,结构清晰.但有些句子,虽没有含条件关系的连词,却也隐含着条件关系,这些句子常用一些词,如but for,without等引出一个介词结构来表示条件,条件常常是虚拟的,或与事实相反的假设.如:
but for若非,要不是
But for the rain,we should have a pleasant journey.要不是下雨,我们的旅行肯定会很愉快.
But for your help,we should not have finished in time.要不是你帮忙,我们肯定不能及时完成任务.
