①当宾语从句中,紧接or not 时,只用whether ,否则都可。Let me know whether/if you can come or not.
②当宾语从句提到句首时,只能用whether ,不能用if。Whether it is true, I can't tell.
③whether 可以引导带to 的不定式,而if不行。I don't know whether to accept.I worry about whether I hurt her feelings.
④whether 可以放在介词后,做介词的宾语,而if不可以。
⑤若if有歧义,只能用whether。Please let me know whether you want to go.( 如果换成 if ,则可能被误解为“如果想来,请告诉我“)
⑥动词discuss, decide, consider, sure等后习惯上也常用Whether引导从句,不用if。Time for her to decide whether she wants to continue the journey.
⑦引导主语从句和表语从句时宜用whether。Whether she will come or not is still a question.她是否能来还是个问题。