whether和if都可以引導(dǎo)賓語從句,表示“是否”,在口語或間接引語中兩者可以互換使用.如：
I wonder if / whether I can get some advice from you.
Ask him whether / if he can come.
但在有些情況下,whether和if的用法有一定區(qū)別.
1.whether引導(dǎo)的從句常可以與連詞or或or not直接連用,而if一般不能.如：
正：Let me know whether you can come or not.
誤：Let me know if you can come or not.
2.當賓語從句提到句首時,只能用whether引導(dǎo),而不能用if.如：
正：Whether it is true or not,I can’t tell.
誤：If it is true or not,I can’t tell.
3.whether可以引導(dǎo)帶to的不定式,if則不能.如：
正：I don’t know whether to accept or refuse.
誤：I don’t know if to accept or refuse.
4.whether及其引導(dǎo)的成分可放于介詞之后,作介詞的賓語,但if不能.如：
正：I worry about whether I hurt her feelings.
誤：I worry about if I hurt her feelings.
5.whether可以引導(dǎo)從句,作主語、表語或同位語,而if不能.如：
正：It was uncertain whether he would come.
誤：It was uncertain if he would come.
正：His first question was whether Tom had arrived yet.
誤：His first question was if Tom had arrived yet.
正：We must consider the question whether we will take these measures.
誤：We must consider the question if we will take these measures.