裕仁天皇葬礼知乎:从句若表“是否”时，if, whether 均可以。

In most cases their functions are the same. The only diffrence is that when you use "whether", you can use the pattern of "whether ... or not". However, when you use "if", you cannot use that pattern.

For examples:

I don't know whether she will come.
or:
I don't know whether she will come or not.

I don't know if she will come.

But, you cannot say:
I don't know if she will come or not.

Besides, sometimes it is not bad to use a different word when too many "if's" are in a sentence.

For an example:

If you are not sure about her decission, why don't you ask her whether she will come to your birthday party or not?

Compare that with the following sentence:

If you are not sure about her decission, why don't you ask her if she will come to your birthday party?

我想你是在问"宾语从句"吧.或者叫"直接引语"变"间接引语". (高一语法重点)

关于引导词:
1. 从句是陈述句
THAT来引导
eg. "I will be back soon."he said.
He said (that) he would be back soon.
2. 从句是一般疑问句
IF,WHETHER都可以
eg. "Will he be back soon?"she asked.
She asked if/whether he would be back soon.
3. 从句是特殊疑问句
疑问词来引导
eg. "When will he be back?" a girl asked.
A girl asked when he would be back.

除此以外还应注意"时态""人称""表示时间地点"等词的变化.

建议去语法网站查阅有关"宾语从句"的章节.

是的 但句中若有or not时，不能用whether