whether与if 引导名词性从句

whether与if 均为"是否"的意思。但在下列情况下，只可用whether：

1. whether引导主语从句并在句首。

eg:Whether he can come to the party on time depends on the traffic.

2. 引导表语从句。

eg:The question is whether we can get in touch with her.

3. whether从句作介词宾语。

eg:I am thinking about whether I should quit my present job.

4.if与whether都可以与or not 连用，但后面紧跟or not 时只能用whether。We didn't know whether or not she was ready.（此时只能用whether）

I wonder whether/if the news is true or not.（此时则二者都可以用）

5. 引导主语从句。

Whether he will come is not clear.

大部分连接词引导的主语从句都可以置于句末，用it充当形式主语。

It is not important who will go.

It is still unknown which team will win the match.

6.引导同位语从句