if和whether有什么区别

3个回答

  • 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,从句用任一种时态;主句为一般过去时,从句则用过去时中的任一种时态.如:

    例6 I don’t know if (whether) he has come here .我不知道他是否来过这儿.

    例7 Tom asked if (whether) I had read the book .汤姆问我是否看过这本书 .

    三、if和whether的区别:

    1 在动词不定式之前只能用whether .如:

    例8 I 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9 I want to know whether it’s good news or not .我想知道是否是好消息.

    3 在介词后,只能用whether.如:

    例10 His father is worried about whether he lose his work .他的父亲担心是否会失去工作.

    4宾语从句放在句首表示强调时,只能用whether .如:

    例11 Whether they can finish the work on time is still a problem .他们是否能准时完成这项工作还是个问题.

    5用if会引起歧义时,只用whether.如:

    例12 Could you tell me if you know the answer

    这句话有两种意思:“你能告诉我是否知道答案吗?”或“如果你知道答案,请告诉我,好吗?”.如用whether可避免歧义.