whether和if的区别和用法

一、引导宾语从句
这时两者的含义区别很小,一般可通用.
I don't know whether/if they will come to help us.
但是,当whether与or not连成一个词组时,whether不可换用if.
I don't know whether or not they will come for our help.
若whether和or not不连在一起,在口语中可以用if取代whether,当然也可以用whether.
I don't care if/whether your car breaks down or not.我不在乎您的车是否是会出故障.
此外,还有三种情况值得注意：
(1)在介词后面只能用whether,不能用if.
I am not interested in whether you'll come or not.
(2)在动词不定式之前,只能用whether,不能用if.
He doesn't know whether to stay or not.
(3)在及物运动discuss后的宾语从句中,只能用whether,不能用if.
We discussed whether we should make a change in our plan.
二、引导主语从句
只能用whether,不能用if.
It is unknown whether he will come.
Whether the news is true remains a question.
三、引导表语从句
只能用whether,不能用if
The question is whether they can take our advice.
四、引导同位语从句
常用whether
The question whether he'll come is unknown.
五、可以用来引导一个否定的宾语从句,whether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.
Tell me if it is not going to rain,please.
六、if除引导宾语从句外,还可以引导条件状语从句,作“是否”解.在容易引起混淆产生歧义的情况下,就不可用if,而须用whether.
Please let me know if you intend to come.这个句子有两种解释：A：“请让我们知道你是否想来.” B：“如果你打算来,请让我们知道.”在书面语中,如果我们想表达的第一种含义,就得用whether来改写第一句.
Please let me know whether you intend to come.
通俗来讲,whether在大多数情况下都可以用,而if则不然,有wether和if时一般选wether不会有错,但是如果所需的意思是"如果",自然只能选if了

whether和if的用法区别
whether与if作“是否”讲,在用法上有相同之处,也有不同之处.
一、相同之处.
1.whether和if都能引导宾语从句,常置于see,ask,learn,tell,wonder,doubt,find out等动词之后.
如：He asked me whether/is I could help him.I want to know whether/if he lives there.
2.whether和if都可用it作形式主语从句中.如：it's uncertain whether/if he'll come this evening.
3.在be uncertain/doubtful之后,常用whether引导宾语从句,有时也可以用if,如：We are uncertain whether/if Mary will come.
二、不同之处.
1.whether可置于句首引导主语从句,而if不能.如：___the 2000 Olympic Games will be in Beijing is not known yet.A.whether B.If C.Whether D.That 答案是C.
2.whether可用在介词之后,引导宾语从句,而If则不能.如：Success depends on whether we make evough effort.
3.whether可引导表语从句,if则不能.如：The puestion is whether it is not worthdoing.
4.在名词之后引导同位语从句时,用whether而不用if.如：The puestion whether the students answered correctly should be decided by the teacher.
5.whether后可接不定式,而if不能.如：Please tell us whether to go or stay here.
6.在有些动词（如discuss）之后,只能用whether,而不用if引导宾语从句.如：We discussed whether we should close the shop.
7.在引导否定概念in宾语从句时,只能用if,而不用whether.如：he asked me if I hadn't finished my work.