if和whether在名词性从句中的用法.ppt

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1、if 和whether在名词性从句中的用法 whether和if都可以用作连词，引导名词性从句，表示“是否”。不同的是whether可以引导所有类型的名词性从句；而if只能引导宾语从句和主语从句。宾语从句宾语从句引导宾语从句既可以用whether，也可以用if，两者常可以互换。whether从正反两个方面提出疑问，选择意义较强，多用于正式文体中；而if多用于口语，比较强调单方面，如：He asked me whether/if I could lend him my bike.Could you tell us whether/if it snows in winter in Australi

2、a?She asked them whether/if they had gone there by car or by train.1.在介词后引导宾语从句只用在介词后引导宾语从句只用whether。lThis depends on whether we are determined to do it.lI am not interested in whether youll come or not.lIm thinking about whether well have a meeting.4点例外点例外2.在及物在及物动词动词discuss，consider等等后的宾语从后的宾语从句中，

3、只能用句中，只能用whether。lWe discussed whether we should make a change in our plan.lWe were discussing whether we should take some measures.lWere discussing whether well go on a picnic.3.宾语从句放在句首表示强调时，只能用宾语从句放在句首表示强调时，只能用whether。lWhether it is true or not,I cant tell.lWhether you have met George before,I ca

4、nt remember.4.引导一个否定的宾语从句，引导一个否定的宾语从句，只用只用if。whether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。lShe asked me if Tom didnt come.lHe considered if he shouldnt tell her the secret.whether/if 引导宾语从句通常可以互换（4点例外）只用whether discuss等后 引导宾语从句放句首表强调 只用if：介词后引导否定的宾语从句1 I d like to invite you to a party this evening.Thank

5、 you,but _ Ill be free I m not sure at the moment.A.while B.if C.when 2-What are you anxious about?-_ A.If we succeed B.That we can succeed C.Do we succeed D.Whether we can succeed3.At the meeting,we discussed _ we should employ more workers.A.if C.that D.不填D.whetherB.whether主语从句注意：注意：whether和和if均可引

6、导主语从句，但均可引导主语从句，但if引导的从引导的从句不能位于句首。句不能位于句首。1.1.引导主语从句引导主语从句并在句首时并在句首时只用只用whether。Whether we go there is not decided.Its doubtful whether/if therell be any seats left.引导表语从句时只用引导表语从句时只用whether。l What we want to know is whether he will come to speak to us tomorrow.lThe doubt was whether you had broken

7、 the beautiful vase.lThe question is whether we can get there on time.表语从句表语从句 引导同位语从句时只用引导同位语从句时只用whether。The question whether well build another lecture building hasnt been settled.The question whether hell come is unknown.We must consider the question whether we will take these measures.同位语从句同位语从

8、句Exercises 1.The question has not been answered _ Taiwan will be included on the Olympic torch relay route.Athat Cwhich Dif 2._ theyll go to the Summer Palace _ the weather.A.If;depends on B.Whether;depends upon C.Whether;depended on D.If;depended uponBwhether1.直接与直接与or not连用时只用连用时只用whether。lI dont

9、know whether or not he will go.lIm not sure whether or not they will come for our help.【注意】若whether和or not不连在一起，在口语中可以用if取代whether。例如：lI am not certain whether/if the train will arrive on time or not.lI dont care whether/if your car breaks down or not.其他情况（其他情况（3点）点）2.在动词不定式之前，只能用在动词不定式之前，只能用whether

10、。lHe doesnt know whether to stay or not.lShe doesnt knows whether to get married now or wait.3.当用当用if会引起歧义时只用会引起歧义时只用whether。if除引导宾语从句外，还可以引导条件状语从句，作“如果如果”解。Please let me know if you intend to come.A：if引导宾语从句,“请让我知道你是否想来。”B：if引导条件状语从句,“如果你打算来，请让我知道。”Please let me know whether you intend to come.EX:Let me know if he has left for Shanghai.请告诉我他是否已经去上海了。如果他已经去上海了，请告诉我一声。Let me know whether he has left for Shanghai.Summary宾语从句（4点）discuss等后whether 宾语从句放句首表强调whether 引导否定宾语从句用if主语从句：表语从句：同位语从句：其他：不定式前用whether if有歧义时用whether引导名词性从句介词后用whether置于句首用whetherwhetherwhetherwhether or not连用Thank you