I f和w h e t h e r的区别if 和 whether都可译为\"是否\",二者引导宾语从句时通常可以互相替换代替 whether.例如：Ask if/whether he plans to come to the meeting.几种情况中 , 只能用 whether:,口语中多用if而以下1.强调两方面的选择 ,特别是句中有 or not 时.如：2.宾语从句前置时 .如：3.引导主语、表语、同位语从句时 .如：Whether the football game will be played depends on the weather.（主语从句）The question is whether he can do it.（表语从句）The question whether we should go with them must be decided at once.（同位语从句）4.在介词之后作介词的宾语时 .如：5.在不定式前与不定式一起组成词组时 . 如：Whether to go or stay is still a question.6. 在 discuss, decide等动词后作宾语时 .如：We discussed whether we should go there by plane.值得注意的是：if 还可以引导条件状语从句 ,是\" 假如；如果 \" 之意 ,而 whether 可以引导让步状语从句 ,是 \" 不管；无论 \" 之意 .如：If you ask him, he will help you.I shall go, whether you come with me or stay at home.一、if 或 whether引导宾语从句时 ,作“是否”讲 , 常放在动词 ask 、see 、say 、know 和 find out 等后面 . 一般情况下 ,两者常可换用 , 在口语中多用 if. 如：例 1 Nobody knows whether (if) it will rain tomorrow.没有人知道明天是否下雨.例 2 Lucy asked whether (if) they had a cotton sweater .露西问他们是否有棉制的羊毛衣 .二、 if 或 whether引导宾语从句时 ,要注意三个方面 ,即连词、语序和时态 .1 if或 whether不能和 that 或其它连词（副词）同时使用,也不能省去 . 如：例 3我不知道他今天是否会来 .[ 误 ] I don ’ t know that if(whether) he will come here today .[ 正 ] I don ’ t know if(whether) he will come here today .例 4他走过来看看猫是否出了毛病 .误] He came to see what if (whether) there was wrong with his cat .[ 正 ] He came to see if (whether) there was wrong with his cat .2 if 或 whether引导的宾语从句时,虽具有疑问意义,但从句语序应用陈述句语序. 如：例5 Did you know the way to the hospital ? The old woman asked me .The old woman asked me .if (whether) I knew the way to the hospital .老妇人问我是否知道去医院的路.3 if 或 whether引导的宾语从句应和主句的时态保持一致. 即主句为一般现在时,从句用任一种；主句一般去, 从句用去中的任一种. 如：例 6I don ’t know if (whether) he has come here .我不知道他是否来儿 .例 7Tom asked if (whether) I had read the book .姆我是否看本 .三、 if 和 whether 的区：1 在不定式之前只能用 whether .如：例 8I can ’ t decide whether to stay.我不能决定是否留下 .2 在 whether ⋯⋯ or not的固定搭配中 . 如：例 9I want to know whether it’s good news or not .我想知道是否是好消息 .3 在介后 , 只能用 whether.如：例 10 His father is worried about whether he lose his work .他的父担心是否会失去工作 .4 从句放在句首表示,只能用 whether . 如：例 11 Whether they can finish the work on time is still a problem .他是否能准完成工作是个 .5 用 if 会引起歧 , 只用 whether.如：例12 Could you tell me if you know the answer ?句有两种意思：“你能告我是否知道答案 ?”或“如果你知道答案 ,告我 , 好 ?” .如用 whether 可避免歧 .if 和 whether专题1)I don't care __________your car breaks down or not.2)This depends upon _________we are determined to do it.3)It depends on _________he is ready.4)I am not interested in _________you'll come or not.5)We haven't settled the question of __________we'll renew oursupplies of coal for factory.6)He doesn't know _________to stay or not.7)I am not sure ___________I'll have time to go with you.8)She doesn't know __________to get married now or wait.9)I don't know _________or not they will come for our help.10)We discussed__________ we should make a change in our plan.11)He considered__________ he shouldn't tell her the secret.12)It is unknown _________he will come.13)I don't know _________they will come to help us.14)I am not certain___________ the train will arrive on time.15)____________the news is true remains a question.16)What we want to know is ___________he will come to speak to ustomorrow.17)The question is ___________they can take our advice.18)Let me know _____________you can ’ t meet me at Jackson and ThroopStreets Wednesday afternoon at two o’ clock.19)We were discussing __________we should discuss the business withthem.20)The question __________we'll build another lecture hasn't been settled.21)The question ____________he'll come is unknown.22)Tell me__________ it is not going to rain, please.23) I don ’ t care ________ he doesn ’ t show up.24)Please let me know __________you intend to come.25)Let me know ___________he has left for Shanghai.1)if/whether2)whether3)whether4)whether5)whether6)whether7)whether/if8)whether9)whether10)whether11)if12)whether13)whether/if14)if/whether15)Whether16)whether17)whether18)if19)whether20)whether21)whether22)if23)if24)whether25)whether。