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1、If 与 whether 的区别归纳 whether和 if 表示“是否”时，两者一般可通用。例如：I dont know whether/if they will come to help us.我不知道他们是否来帮助我们。I am not sure whether/if Ill have time to go with you.我很难说我们是否有时间跟你们一起去。He asked me whether I could lend him my bike.Could you tell us whether/if it snows in winter in Australia?I want to
2、 know whether/if you can come or not?但在以下情况下只能用 whether：1）在表语从句中 The question is whether the film is worth seeing.The key point is whether you are fit for the dresses.关键是你适不适合穿那些裙子。2）在同位语从句中 The news whether our team has won the match is unknown.Answer my question whether you are coming.要不要嫁给我，请给我一个
3、明确的答案。Please give me an obvious answer whether you are willing to marry me.3）在主语从句中 Whether we shall attend the meeting hasnt been decided yet.=It hasnt been decided yet whether we shall attend the meeting.姚明是否退役是前天人们关注的焦点.Whether YaoMing would retire was the focus of attention the day before yester
4、day.如果用 it 作形式主语，则 whether和 if 都可以引导主语从句。如：It hasnt been decided whether/if we shall attend the meeting.4）在介词之后（介词往往可以省略）It all depends(on)whether they will support us.I am not interested in whether youll come or not.你来不来我不感兴趣。5）后面直接跟动词不定式，即 whether to do He doesnt know whether to stay or not.他不能知道是
5、否要留下来。She doesnt know whether to get married now or wait.是否现在结婚或是等待她不知道。6）后面紧接 or not，即 whether or not We didnt know whether or not she was ready.注意：当 or not不是紧跟在其后时，两个都可以用。I dont care whether or not your car break down.=I dont care whether/if your car break down or not.7）用 if 会引起歧义时 Please let me k
6、now if you like it.这句话有两种意思：“请告诉我你是否喜欢”或“如果你喜欢，请告诉我。”用了whether就可以避免歧义。8）宾语从句放在句首表示强调时（所有从句提前表示“是否 时都用 whether;if引导从句放在句首时表示“如果”）Whether they can finish the work on time is still a problem.9）用于句型“名词+as to+whether”中。There is some question as to whether the public should be told about the accident.（此处
7、question表示“疑虑”，是抽象名词，不可数）10)advice、consider、discuss 等动词后接宾语从句用 whether 不用 if 引导。You should consider carefully whether the car you are interested in is good value.They are discussing whether they should put off/postpone the sport meeting.他们在讨论是否该推迟运动会。只用 if 不用 whether的情况：一、笼统地讲，if 可以用来引导一个否定的宾语从句，whe
8、ther则不能用来引导否定的宾语从句，因为它表示正反两方面的选择意义比较强。例如：Tell me if it is not going to rain,please.请告诉我明天是否不会下雨。He considered if he shouldnt tell her the secret.他考虑他是否不该告诉她这个秘密。二、若要细究，Whether 引导的从句一般不可以为否定结构（选选择问句的后一部分除外）；而 if 则可以跟否定结构。如：I dont care if she doesnt come.I dont care if it doesnt rain.但是，在某些动词或者形容词之后，则
9、可以用 whether 引导一个否定结构的句子，这种结构往往表示肯定的意义。如：I wonder whether he doesnt think too much of himself.其意思相当于 I think he does think too much of himself.【相关链接】doubt“怀疑”后接宾语从句时 whether，if，that 的用法：1）主句为肯定句时，I doubt whether/if表示“我怀疑”，；而 I doubt that 表示“认为未必可能”。（一般采用 I doubt whether/if）I doubt whether/if he will come soon.我怀疑他是否会来。（批判语气）I doubt that he will come soon.我认为他未必会来。（客观语气）2）主句为否定或疑问句，则应该用 that。I dont doubt=I am sure=I bet Do you doubt that he will come soon?I dont doubt that he will come soon.我相信他会来。I dont doubt that he will succeed.我相信他会成功。There is no doubt that