由whether,if 引导的宾语从句（一）由whether,if 引导的宾语从句
由whether(if)引导的宾语从句，实际上是一般疑问句演变而来的。意思是“是否”。宾语从句要用陈述句语序。一般说来，在宾语从句中whether与if可以互换使用，但在特殊情况下if与whether是不能互换的。
例句：I wonder whether(if) they will come to our party.
（二）只能用whether，不能用if引导的宾语从句
1.在带to的不定式前：We decided whether to walk there.
2.在介词的后面：I’m thinking of whether we should go to see the film.
3.直接与or not连用时
例句：I can’t say whether or not thet can come on time.
4.当强调宾语从句并将其提前时只能用whether。
如:Whether I'll have time to go with you I am not sure.我很难说我们是否有时间跟你们一起去。
5.当whether和or 连用表示明确的选择时。
如:He asked me whether I wanted to go there by train or by bus.他问我是想乘火车还是坐公共汽车去那里。
6.动词discuss，decide,consider，sure等后习惯上也常用Whether引导从句，不用if。
They discussed whether they should leave at once.他们讨论了是否应该马上离开。
We discussed whether the house should be sold. 我们讨论了这房子是否应卖掉。
（三）其他只能用whether不能用if的情况
1.表语从句用whether引导不用if.
如:①The doubt was whether you had broken the beautiful vase. 疑问是你是否打坏了这只漂亮的花瓶。
2 同位语从句用whether引导不用if.
如: The question whether we'll build another lecture building hasn't been settled.
是否要另建一幢教学楼的问题还未决定。
3位于句首的主语从句 只能用.whether。
如： Whether they win or lose is all the same to me. 他们是赢是输於我都一样.（此时whether不能换作if ）
It's doubtful whether there'll be any seats left. 说不上还有没有空座位了. (此句whether能换作if)
只能用if不能用whether引导的宾语从句
1.if引导条件状语从句，意为“如果”
例句：The students will go on a picnic if it is sunny.
2.if引导否定概念的宾语从句时
例句：He asked if I didn’t come to school yesterday.
3.引导状语从句even if（即使）和as if（好象）时
例句：He talks as if he has known all about it.
强化练习：
B1，We will go swimming ---------- it is fine tomorrow．
A. while B. if C. when D. whether
A2. You have not yet answered my question _____ I can join in the party tonight or not.
A. whether B. if C. that D. which
D3．— I d like to invite you to a party this evening.
— Thank you, but _____ I’ll be free I m not sure at the moment.
A. while B. if C. when D. whether
D4．---What are you anxious about?
---___________
A. If we succeed B.That we can succeed C. Do we succeed D.Whether we can succeed
C5. Only when _____ the painting _____ decide ______the painting is worth buying.
A. he sees, he can ,whether B. does he see, can he, if
C. he sees, can he ,whether D. sees he, he can,that
A6. _____ English is his favourite subject
A. I asked him if B. I asked him that whether thC. I asked him that D. I asked him which
B7. _____ they’ll go to the Summer Palace ____ the weather.
A. If; depends on B. Whether; depends upon C. Whether; depended on D. If; depended upon
C8.It isn’t quite _____ ______ he will be present at the meeting.
（it is 。。。that 结构中只能有certain不能用sure）
A. sure; whether B. sure; if C. certain; whether D. certain; that
B9He asked me if I hadn't finished my homework．他问我是否没有完成作业。
A. while B. if C. when D. whether
B10. No one was sure _____ he would be asked to speak next year.
A. when B. whether C. what D. how
B11. I doubt _____ he will come here on time.
A. that B. whether C. when D. where