Question

什么情况下只用whether不用if

Answer 1

1.在表语从句和同位语从句中。
例如：The question is whether the film is worth seeing.
The news whether our team has won the match is unknown.
2.在主语从句中，只有用it作形式主语时,whether和if 都能引导主语从句，信冲否则，只能用whether
例如：Whether we shall attend the meeting hasn’t been decided yet.
It hasn’t been decided whether (if) we shall attend the meeting.
3.在介词樱带之后。（介词往往可以省略）。
例如: It all depends (on) whether they will support us.
4.后面直接跟动词不定式时。
例如：He doesn’t know whether to stay or not.
5.后面紧跟时or not。
例如：We didn’t know whether or not she was ready.
6.引导让步状语从句时。
例如：Whether you like it or not ,you must do it well.
7.用if会引脊坦芦起歧义时。
例如；Please let me know if you like it.该句有两个意思：“请告诉我你是否喜欢”或“如果你喜欢，请告诉我。”用了就可以避免。
8.在discuss后

Answer 2

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作形式主语从句差磨中。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：虚简斗 The puestion is whether it is not worthdoing.
4.在名词之后引导同咐袜位语从句时，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.

Answer 3

1.在表语从句和戚局同位语从句中。
例如：The question is whether the film is worth seeing.
The news whether our team has won the match is unknown.
2.在主语从句中，只有用it作形式主升胡语时,whether和if 都能引导主语从句，否则，只能用whether
例如：Whether we shall attend the meeting hasn’t been decided yet.
It hasn’t been decided whether (if) we shall attend the meeting.
3.在介词之后。（介词往往可以省略）。
例如: It all depends (on) whether they will support us.
4.后面直接跟动词不定式时。
例如：He doesn’t know whether to stay or not.
5.后面紧跟时or not。
例如：高笑让We didn’t know whether or not she was ready.
6.引导让步状语从句时。
例如：Whether you like it or not ,you must do it well.