关于whether与ifI have no idea whether to visit my grandparents this Sunday.这句句子当中为什么只能用whether,不能用if?请详细回答````

关于whether与ifI have no idea whether to visit my grandparents this Sunday.这句句子当中为什么只能用whether,不能用if?请详细回答````
关于whether与if
I have no idea whether to visit my grandparents this Sunday.
这句句子当中为什么只能用whether,不能用if?
请详细回答````

关于whether与ifI have no idea whether to visit my grandparents this Sunday.这句句子当中为什么只能用whether,不能用if?请详细回答````
这个句子只能用whether,不能用if的原因是whether可以引导带to的不定式,if则不能.
我详细地列出来,你看看...
whether和if都可以引导宾语从句,表示“是否”,在口语或间接引语中两者可以互换使用.如：
I wonder if / whether I can get some advice from you.
Ask him whether / if he can come.
但在有些情况下,whether和if的用法有一定区别.
1.whether引导的从句常可以与连词or或or not直接连用,而if一般不能.如：
正：Let me know whether you can come or not.
误：Let me know if you can come or not.
2.当宾语从句提到句首时,只能用whether引导,而不能用if.如：
正：Whether it is true or not,I can’t tell.
误：If it is true or not,I can’t tell.
3.whether可以引导带to的不定式,if则不能.如：
正：I don’t know whether to accept or refuse.
误：I don’t know if to accept or refuse.
4.whether及其引导的成分可放于介词之后,作介词的宾语,但if不能.如：
正：I worry about whether I hurt her feelings.
误：I worry about if I hurt her feelings.
5.whether可以引导从句,作主语、表语或同位语,而if不能.如：
正：It was uncertain whether he would come.
误：It was uncertain if he would come.
正：His first question was whether Tom had arrived yet.
误：His first question was if Tom had arrived yet.
正：We must consider the question whether we will take these measures.
误：We must consider the question if we will take these measures.

后面是to do的话只能用whether

1、引导宾语从句
在引导宾语从句时，whether 和if 通可以互换，在ask,care,doub,know,learn,msee,tell,try,wonder等动词之后尤其如此。例如：
I don’t know if/whether I can help you.
They don’t care a bit whether my reports are good...

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1、引导宾语从句
在引导宾语从句时，whether 和if 通可以互换，在ask,care,doub,know,learn,msee,tell,try,wonder等动词之后尤其如此。例如：
I don’t know if/whether I can help you.
They don’t care a bit whether my reports are good or bad..
I wonder if you can examine him now.(高一册第十四页)
I am not sure if/whether I’ll have time.
但是，必须注意以下几点：
1）如果从句是否定结构，则用if不用whether.例如：
Well,think,and see if the most religious people aren’t those who fell that this life doesn’t gice them all they want.好，你想，那最虔诚的宗教徒，是不是就是那此觉得这现实的人生没有完全满足自己欲望的人？
Dinner was almost over when Dan,still looking hungry,grinned and asked Dave if he wasn’t going to have some bread.晚饭快吃完的时候丹（他看上去还没吃饱）笑着问戴维还要不要吃些面包。
I don’t care if he doesn’t show up .他来不来我都不在乎。
Let me know if you can’t meet me at Jackson and Throop Streets Wednesday afternoon at two o’clock.星期三下午奉告警方，你是否能在杰逊街和思鲁街的黑心角来跟我相会。（＜嘉莉妹妹＞＝
当然，对某些句子，人们可能会有不同的理解。如上面最后两列中的if 也可理解为引导条件状语从句：
他不来我也不在乎。
如果 你在星期三下午二时不能和我在杰克逊街和思鲁街的黑心角相会，请通知我。
但是，当doubt是还定式时，则不用whether或if，要改用that,因为句子本身已没有“怀疑”或选择之意。度比较：
I don’t doubt that you are honest.我不怀疑你的诚实。
She never doubt for a moment that she was right.她对自己是正确的这一点从不怀疑。
I doubt whether it’s true.
I doubt if that was what he wanted.
2)宾语从句前置时只能用whether,如：
Whether he lives there,I want to know.
Whether this is true or not ,I can’t say.
Whether we can relly help ypu ,I don’t know yet .我们是否真的能帮助你，我还不知道。
3）在decide,dicuss等动词后，通常只跟whether引导的宾语从句。如：
They dicussed whether they should close the shop.他们痔疮了是不是该关掉商店。
The old lady has not decided whether she will live with her daughter in the countryside.
4)出现在介词后面的宾语从句只能用whether引导，如：
The teacher worried about whether he had hurt the girl’s feelings.老师担心他是否伤害了女孩的感情。
It all depends on whether she likes the boss or not .一切都取决于她是否喜欢这位上司。
It depends on whether the crystal can emit a powerful beam of light.这取决于晶体是否会发射出一束强光。
5）句中含有引导条件状语从句的if 时，用whether 不用if，如：
Bill asked whether ,if I got the job,I’d move to York.比尔问如果我得到这份工作是否还要迁到约克。
6）在现代英语中似乎有一种趋势，即说话人期望得到或估计会得到肯定答复时常用if ，而在对答复时的肯定与否定没把握或不在意时则用whether.例如：
He asked me if he could come.他问我他可不可以来。（暗示he想来）
He asked me whether he should come (or not ).他问我他是否该来。（暗示他对来不来都无所谓）
7）在有些句子中，用if引导宾语从句可能会导致歧义的产生。因此，若要表达选择的含义最好用whether.例如：
You should tell your mother whether you want to go with her for a holiday.你应该告诉你母亲你是否想和好一起度假。（若用if则可能被理解为是条件从句：如果你想和你母亲一起度假，你就应当告诉她。）
Let me know whether you are coming.告诉我你来不来。（若把句中的whether改为if ,则可能 表示：如果你要来，请通知我）
2．引导主语从句
主语从句位于句首时，用whether 不用if ,本文开关的高考题即属此种情况。再如：
Whether they win or lose is all the same to me.
Whether it will do us harm or good remains to be seen.
但是，当采用形式主语it,而将主语从句后置时，用whether和if 均可（尽管whether更常用）：
It makes no difference to me whether/if it’s foggy or clear..(高二册，第220页)
It’s doubtful if he is coming.
It’s not clear to me whether/if she likes the present.（＜英语语法大全＞第1456页＝
It was not known whether/if hi would ask.(＜大学共同市场讲法＞第397页＝
3．引导表语从句
引导表语从句时，一般用whether.例如：
The question is whether they can cooperate with us.问题是他们能否与我们合作。
The question I whether we can get there in time.
有的语法认为if 也可以引导表语从句，例如：
The first question I put to him was whether/if he would do it.
Our only problem is if someone gets that brilliant notion first.
不过，对中学生来说，这种用法还是尽时不时避免为好。
4．引导宾语从句
引导同位语从句时一般用whether.例如：
The question whether he should come himself or send a substitute must be decided upon,他该亲自来还是派人替他来，这个问题必须定下来。
We will soon discuss the problem whether we should take some effective measures to protect the animals and plants in our region.我们很快将讨论是否应该采取一些有效措施来保护本地区的动植物这一问题。
5．引导让步状语从句
1)引导让步状语地，一般用whether.例如：
Whether you like it or not ,you’ll have to do it .
Whether the weather is good or bad ,they will set off as they planned.无论天气是好是坏，他们都将按计划启程。
The moon is a moon still, whether it shines or not .(Proverb)
2）whether还可与分词、介词短语构成短语，在句中作让不状语，此时不可用if 来替代whether::
Whether waking or sleeping ,he breathes noisily.他不管是醒着还是睡着了，都是呼呼作声。
It is decided, whether for better or worse.不管前途好坏，此事已定。
Whether by accident or design, they met.无论是巧遇还是有意安排，反天他们是见面了。
6．与不定式连用
在不定式之前用whether，如：
He doesn’t know whether to stay or not .(MET’87)
We were wondering whether to go today or tomorrow .
The problem is whether to go by bus or by plane.
It has not been decided yet whether to give the English oral test this Friday.本星期五是否举秆英语口试还没有决定。
7．与or ,or not 连用
1）whether 侧彼一时“选择”、“怀疑”，所以一些语法家认为只有whether 才可以和or ,or not ,or no连用，构成whether…or,whether…or not等结构，而if则不能用于这些结构。例如：
I don’t know whether I should go away or stay here.
Whether they do it or not matters little to us.他们干还是不干，与我们关系都不大。
What I want to know is whether the professor will come here or not next week.我想知道的是教授下周还来不来。
The little girl asked ger father whether she should go to the party or not .女孩问父亲她应不应该参加这个晚会。
I don’t know whether it is raining or not .
但是，随着语言的发展，if与or,or not 用也已为人们所接受，例如：
He didn’t know whether /if we should write or phone.(＜最新牛津现代高级英汉汉英双解词典＞＝
How can you tell if the charge is positive or negative?你怎么知道电荷是下的还是负的？（＜英汉技术词典＞＝）
I wonder if /whether he is at home (or not )_.(Harold E.Palmer:A Grammat of English Words)
I don’t care if/whether you car breaks down or not .(Geoffrey Jan Svartvik:A Communicative Grammar of English )
I don’t think she cares if we’re absent or not.(《现代成则为王用法词典》)
Let me know whether/if you can come or not .(Michael Swan: Practical English Usage)
然而，直接与or not连用时，则只能用whether ,换句话说，只有whether or not ,没有if not:
I don’t know whether or not you ‘ll come.
2)if…not 和whether …not 都可以两个从句，这时应重复if 和whether:
I asked him whether he had done all the work himself or whether he had had any assistance.我问他这些工作是他一个人干 的还是有人帮助。
I can’t find out if the flight has been delayed or if it has been cancelled.我不清楚班机是扒迟了还是被取消了。
I don’t know if it was on account of Dan’s arguing with him ,or if it was because there was no bread for dinner, that Dad was in a bad temper .爸爸尽情不好，我不知道到底是因为丹和他争论，还是因为晚饭没有面包。

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