if的用法

Question

if wether 可以引导从句吗 它们怎样使用 有什么不同吗

Answer 1

whether和if作为连接词都可表示“是否”之义，但两词的用法各有异同。下面举例说明。

1．whether和if都可用于引导宾语从句。如：

Do you know if／whether she's coming？你知道她是否要来？

但是，若宾语从句是否定句时则宜用if。如：

I don't care if she doesn't come．我不管她来不来。

2．whether和if都可在be doubtful、 unsure、uncertain等词后面引导一个从句作为主语补语。如：

I'm unsure if ／whether they're doing their best．我不能肯定他们是否正在尽力干。

3．whether可引导主语从句，if则不能。如：

Whether you can stay with my mother is another matter．你是否能与我母亲呆在一块是另一回事。

4．whether可引导表语从句，if则不能。如：

The question is whether this material can be used in our factory．问题是我们厂能否使用这种材料。

5．从句位于主句前，whether可用于句首，if则不能。如：

Whether he is ready，I don't know．他是否准备好了，我不知道。

Whether it is true（or not），I don't care．是否真的，我不在乎。

6．whether可引导介词宾语从句，if则不能。如：

It depends on whether he will arrive．那要看他是否到达而定。

We haven't settled the question of whether（不能用if）we'll give up our right．我们尚未决定我们是否放弃我们权利的问题。

7．whether可用于不定式前，if则不能。如：

She doesn't know whether to get mar- ried now or wait for a few years．她不知道现在结婚还是再等几年。

8．在正式文体中表达两种选择而不省略其一时，一般用whether．．．or not，而不用if．．．or not。如：

Tell me beforehand whether you will join us or not．请事先告诉我你们参加还是不参加。

9．在某些动词后，如discuss，习惯用 whether，而不用if。如：

We discussed whether we should close the shop．我们讨论了是否应该关闭那个商店。

10．在使用if易产生歧义时，应使用 whether，请比较：

Let me know whether you are coming．告诉我你是否要来。

Let me know if you're coming．如果你来，请通知我。

11．如果主句已有一个if引导的条件句，为了避免产生混淆，应使用whether。如：

He asked me whether，if there was enough time，I wanted to go to his office．他问我如有足够的时间是否想去他的办公室。

给我加点分哦~~~

Answer 2

whether和if的用法分析

一、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.
二、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 worth doing.
4.在名词之后引导同位语从句时，用whether而不用if。如： The question 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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whether和if都可以引导宾语从句，表示“是否”，在口语或间接引语中两者可以互换使用。如：
I wonder if / whether I can get some advice from you.

Ask him whether / if he can come.

但在有些情况下，whether和if的用法有一定区别。

1. whether引导的从句常可以与连词or或or not直接连用，而if一般不能。如：

正： Let me know whether you can come or not.
误： Let me know if you can come or not.

2. 当宾语从句提到句首时，只能用whether引导，而不能用if。如：

正： Whether it is true or not, I can’t tell.
误： If it is true or not, I can’t tell.

3. whether可以引导带to的不定式，if则不能。如：

正： I don’t know whether to accept or refuse.
误： I don’t know if to accept or refuse.

4. whether及其引导的成分可放于介词之后，作介词的宾语，但if不能。如：

正： I worry about whether I hurt her feelings.
误： I worry about if I hurt her feelings.

5. whether可以引导从句，作主语、表语或同位语，而if不能。如：

正： It was uncertain whether he would come.
误： It was uncertain if he would come.

正： His first question was whether Tom had arrived yet.
误： His first question was if Tom had arrived yet.

正： We must consider the question whether we will take these measures.
误： We must consider the question if we will take these measures.本回答被提问者采纳

Answer 3

1. (表示条件)如果 ,主句用将来时，if从句用现在时表示将来
He will come if you invite him.
如果你请他,他会来的。
2. (表示虚拟)假如,要是

1）时态：可以表示过去，现在和将来的情况。它的基本特点是时态退后。
a. 同现在事实相反的假设。
句型 ： 条件从句 主句
一般过去时 should( would) +动词原形
If they were here, they would help you.

b. 表示于过去事实相反的假设。
句型： 条件从句 主句
过去完成时 should(would) have+ 过去分词
If she had worked harder, she would have succeeded.
The rice would not have been burnt if you had been more careful.
If my lawyer had been here last Saturday, he would have prevented me from going.

If he had come yesterday, I should / would have told him about it.
含义：He did not come yesterday, so I did not tell him about it.
If he had not been ill and missed many classes, he would have made greater progress.
含义： He was ill and missed many lessons, so he did not make greater progress.

c. 表示对将来的假想
句型： 条件从句 主句
一般过去时 should+ 动词原形
were+ 不定式 would + 动词原形
should+ 动词原形
If you succeeded, everything would be all right.
If you should succeed, everything would be all right.
If you were to succeed, everything would be all right.

3. 是否 = whether 连接宾语从句
I wonder if she is ill.
不知她是否病了。