whether和if都可以引导宾语从句，表示“是否”，在口语或间接引语中两者可以互换使用。如：
I wonder if/whether I can get some advice from you.
Ask him whether/if he can come.
1.whether引导的从句常可以与连词or或or not直接连用，而if一般不能。如：
正：Let me know whether you can come or not.
误：Let me know if you can come or not.
2.当宾语从句提到句首时，只能用whether引导，而不能用if。如：
正：Whether it is true or not, I can't tell.
误：If it is true or not, I can't tell.
3.whether可以引导带to的不定式，if则不能。如：
正：I don't know whether to accept or refuse.
误：I don't know if to accept or refuse.
4.引导表语从句时不用if。如：
The question is whether we can get there on time.
问题是我们能否按时到达那里。
5.引导同位语从句时不用if。如：
He asked me the question whether the work was worth doing.
他问我这个问题，那项工作是否值得做。
6.whether及其引导的成分可放于介词之后，作介词的宾语，但if不能。即在介词后引导宾语从句不用if。如：
正：I worry about whether I hurt her feelings.
误：I worry about if I hurt her feelings.
7.宾语从句置于句首时不用if。如：
Whether you have met George before, I can't remember.
我不记得你以前是否见过乔治。
8.在discuss等之后时不用if。如：
We're discussing whether we'll go on a picnic.
我们在讨论是否要去野餐。
9.在动词不定式前用whether不用if。如：
He doesn't know whether to go or not.
他不知道是否去。
10.宾语从句是否定式时不用whether。如：
She asked me if Tom didn't come. 她问我Tom是不是没有来。
11.whether可以引导从句，作主语、表语或同位语，而if不能。如：
正：It was uncertain whether he would come.
误：It was uncertain if he would come.
正：His first question was whether Tom had arrived yet.
误：His first question was if Tom had arrived yet.
正：We must consider the question whether we will take these measures.
误：We must consider the question if we will take these measures.
12.当用if会引起歧义时不用if。如：
Please let me know whether you are busy. 请告诉我你是否忙。
(若用if，还可理解为“如果你很忙，你就告诉我。”)
。