是whether 和 if
一、whether和if都可以用作連詞,引導(dǎo)一個(gè)名詞性從句,表示“是否”.whether可以引導(dǎo)主語從句、表語從句、賓語從句和同位語從句；而if只能引導(dǎo)賓語從句.
1．引導(dǎo)賓語從句既可以用whether,也可以用if,兩者?？梢曰Q.whether從正反兩個(gè)方面提出疑問,選擇意義較強(qiáng),多用于正式文體中；而if多用于口語,比較強(qiáng)調(diào)單方面,如：
He asked me whether / if I could lend him my bike.
Could you tell us whether / if it snows in winter in Australia?
I want to know whether / if you can come or not.
She asked them whether / if they had gone there by car or by train.
值得注意的是：
①whether 和if都可以和or not連用,但是whether之后可以直接跟or not,而if則不能,如：
I don’t care whether or not your car breaks down.
I don’t know whether or not he’s coming.
但是不可以說：
I don’t care if or not your car breaks down.
② whether引導(dǎo)的從句一般不可以為否定結(jié)構(gòu)（選擇問句的后一部分除外）；而if則可以跟否定結(jié)構(gòu),如：
I don’t care if she doesn’t come.
I don’t care if it doesn’t rain.
但是,在某些動(dòng)詞或形容詞之后,則可以用whether引導(dǎo)一個(gè)否定結(jié)構(gòu)的句子,這種結(jié)構(gòu)往往表示肯定的含義,如：
I wonder whether he doesn’t think too much of himself.
其意思相當(dāng)于：I think he does think too much of himself.
③ 在個(gè)別動(dòng)詞之后,如discuss 等,只跟用whether引導(dǎo)的賓語從句,如：
They discussed whether they should close the shop.
We discussed whether Mary could join us.
④ whether 可以引導(dǎo)從句作介詞的賓語,而if則不能,如：
I’m not interested in whether they’ll go or not.
It depends on whether we have got enough money.
⑤ whether可以直接跟動(dòng)詞不定式連用,而if則不能,如：
I didn’t know whether to laugh or to cry.
She hasn’t decided whether to go or not.
He was wondering whether to go home or stay at school.
2．引導(dǎo)主語從句（包括從句在句首的位置）應(yīng)當(dāng)用whether,不用if,如：
Whether it is true remains a problem.
Whether he can stay with us is another matter.
Whether he will come, I am not sure.
Whether or not he did it, I cannot tell.
3．引導(dǎo)表語從句用whether,不用if,如：
The question is whether you should accept it.
The question is whether he will speak at the meeting.
4．引導(dǎo)同位語從句用whether,不用if,如：
The question whether he’ll attend the meeting is essential.
I am in doubt whether I should agree to the plan.
二、whether 還可以引導(dǎo)讓步狀語從句,意為“不管；無論”；而if則不能引導(dǎo)這種從句,如：
I shall tell her about it whether you agree or not.
Whether or not the figures are accurate, we have to recheck them.
Whether or not we had a baby, we could not survive just on my salary.
三、if還可以引導(dǎo)條件狀語從句,意為“如果；假如”,而whether則不能引導(dǎo)這種從句,如：
We shall do this experiment if we have time.
四、如果在從句中使用if表示“是否”容易與表示條件的狀語從句混淆時(shí),應(yīng)注意避免使用if,例如：Please let us know if they are coming. 這句話可以理解為“如果他們要來,請通知我們一下.”也可以理解為“請告訴我們,他們是否要來.”若表示后一層意思,應(yīng)當(dāng)使用,以免引起誤會(huì).
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jiangxl |Lv13 | Answer Date：2009.10.21 16:11 (0) | (0) 1. 在動(dòng)詞不定式之前只能用whether .如：
例 I can’t decide whether to stay. 我不能決定是否留下.
2 在whether …… or not 的固定搭配中.如：
例 I want to know whether it’s good news or not . 我想知道是否是好消息.
3 在介詞后,只能用whether.如：
例 His father is worried about whether he lose his work . 他的父親擔(dān)心是否會(huì)失去工作.
4賓語從句放在句首表示強(qiáng)調(diào)時(shí),只能用whether .如：
例whether they can finish the work on time is still a problem . 他們是否能準(zhǔn)時(shí)完成這項(xiàng)工作還是個(gè)問題.
5用if會(huì)引起歧義時(shí),只用whether.如：
例 Could you tell me if you know the answer ?
這句話有兩種意思：“你能告訴我是否知道答案嗎?”或“如果你知道答案,請告訴我,好嗎?”.如用whether可避免歧義
希望對你有幫助 如有疑問 請?jiān)诰€交談 祝你考上理想的學(xué)校 O(∩_∩)O