“条件”表达法是中学英语中相当重要的语言现象，也是高考测试的重点和难点，为使同学们更好的复习和运用，减少失误，现就其相关知识与考点作如下归纳分析：
条件即一个动作或一种情况发生存在的前提，有真实条件和非真实之分。简述如下：
一 从句
常用来引导条件从句的连词有：if，unless，even if ，in case ，as long as，so long as，so far as ，
On condition that，
1 考查in case 引导条件句的用法
[NMET2000] I don’t think I’ll need any money but I ‘ll bring some_____.
A at last B in case C once again D in time
【解析】本题考查in case 引导条件句的用法,答案为: B ..in case引导条件句,其意为“假使；以防（万一）”。其位置较为灵活，可置于句首或句尾 。其时态常用一般现在时表示将来，但也可用“should﹢动词原形”。
例如：Be quiet in case you should wake the baby
【测试演练】（2000春季京皖卷）(答案: C)
John may phone tonight。I don’t want to go out____he phones.
A as long as B in order that C in case D so that
2考查if 引导条件句的用法
[NMET2000] The WTO can’t live up to its name____ it does not include a country that is home to one fifth of mankind
A as long as B while C if D even though
【解析】本题考查If 引导条件句的用法,答案为: C. 在if 引导的条件句中,应注意 时态的对应性,一般来说,if引导的条件句常用一般现在时或现在完成时表示将来而主句常用一般将来时,祈使句或情态动词的一般式.
【测试演练】(MET1992) (A)
If city noises ___ from increasing, people ____ shouted to be heard even at the dinner table
20 years from now .
A are not kept ;will have to B are not kept ; have to
C do not keep ;will have to D do not keep; have to
3 考查unless 引导条件句的用法
[NMET1992] You will be late ___you leave immediately.
A unless B until C if D or
【解析】答案：A 。unless 引导的从句，意义为“除非，如果不”相当于“if….not”
4考查if 引导省略条件句的用法
[上海高考卷1998] If ____the same attention again, he is sure to get well
A giving B give C given D being given
【解析】答案：C .在条件状语从句中,如果从句的主语与主句的主语一致,且从句中有系动词be,可以将从句主语及be 省去,构成省略.
5考查if省略的条件句的用法
[上海高考卷1994] it rain tomorrow ,we would have to put off the visit to the Yangpu Bridge
A Were B Should C Would D Will
【解析】答案：B .本题属于虚拟语气倒装形式.若省略if可将were,( had ,should )提到句首
变为倒装形式。
If I were at school again，I would study harder
→Were I at school again，I would study harder
If you had come earlier，you would catch the bus。
→Had you come earlier，you would catch the bus。
【易错点解析】若省略的条件句中的谓语动词是否定形式时，不能用动词缩写形式。
误：Weren’t it for the expense ,I would go abroad now
正;Were it not for the expense ,I would go abroad now