if weather 的区别 weather,if如何区别(条件状语从句中的!

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.

相同之处。

1.whether和if都能引导宾语从句，常置于see,ask,learn,tell,wonder,doubt,find out等动词之后。

如：He asked me whether/is I could help him. I want to know whether/if he lives there.

2.whether和if都可用it作形式主语从句中。如： it's uncertain whether/if he'll come this evening.

3.在be uncertain/doubtful之后，常用whether引导宾语从句，有时也可以用if，如： We are uncertain whether/if Mary will come.

不同之处。

1.whether可置于句首引导主语从句，而if不能。如： ___the 2000 Olympic Games will be in Beijing is not known yet. A.whether B.If C.Whether D.That 答案是C。

2.whether可用在介词之后，引导宾语从句，而If则不能。如： Success depends on whether we make evough effort.

3.whether可引导表语从句，if则不能。如： The puestion is whether it is not worthdoing.

4.在名词之后引导同位语从句时，用whether而不用if。如： The puestion whether the students answered correctly should be decided by the teacher.

5.whether后可接不定式，而if不能。如： Please tell us whether to go or stay here.

6.在有些动词（如discuss）之后，只能用whether，而不用if引导宾语从句。如： We discussed whether we should close the shop.

7.在引导否定概念in宾语从句时，只能用if，而不用whether.如：he asked me if I hadn't finished my work

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