在复合句中，充当宾语的成分是一个句子，这个句子代替了原来用一个词表示的宾语，称之为宾语从句。置于动词、介词等词性后面，在句子中起宾语用途的从句叫做宾语从句。在英文学习的时候，这部分语法内容要好好来学习。
具体结构为：主句+引导词+宾语从句
譬如：
简单句：We knew that.
复合句：We knew that we should go home.
宾语从句分为三类：动词的宾语从句，介词的宾语从句和形容词的宾语从句。
谓语动词、介词、动词不定式，v.-ing形式后面都能带宾语从句，有的形容词之后也可以带宾语从句。
宾语从句过"三关"：语序，引导词，时态。
动词、介词、形容词后的宾语从句
1)动词+宾语从句
We knew that we should go home.
这种动词一般是及物动词，即后面能直接加宾语的动词，譬如：give, tell 等。
但像"arrive"就不可以直接加宾语，假如要加宾语，后面需要加介词。
2)介词+宾语从句
They are talking about whether it will rain tomorrow.
容易见到介词：in, at, on 等等。
3)形容词+宾语从句
I am sure that he can come on time.
后面可以直接加宾语从句的形容词有：
pleased, glad, happy, afraid, surprised, certain, sorry等。
语序
无论主句是陈述句还是疑问句，宾语从句都需要用陈述语序，即“主句+连接词+宾语从句”句式。
依据连接词在从句中所担任的不同成分，可分为以下四种：
1)连接词+谓语。连接词在从句中作主语。容易见到的连接词有: who, what, which等。
Could you tell me who knows the answer，please?
你能告诉我哪个了解答案吗?
The small children don't know what is in their stockings.
这类孩子子不了解袜子里有哪些东西。
2)连接词+名词+谓语。连接词在从句中作主语的定语。容易见到的连接词有: whose, what, which, how many, how much等。
He asked whose handwriting was the best in our class.
他问大家班上哪个的书法最好。
The teacher asked us how many people there were in the room.
老师问大家房间里有多少人。
3)连接词+主语+谓语。连接词在从句中作宾语、状语或表语。容易见到的连接词有: who, what, which, how many, how much, when, why, how, where, if/whether等。
He hasn't decided if he'll go on a trip to Wuxi.
他还没有决定是不是去无锡旅游。
Could you tell me what I should do with the money?
你能告诉我我怎么样处置这笔钱吗?
4)连接词+名词+主语+谓语。连接词在从句中作宾语或表语的定语。容易见到的连接词有: what, which, how many, how much, how等。
Do you know which class he is in?
你了解他在什么班吗?
She asked me if I knew whose pen it was.
她问我是不是了解这是哪个的钢笔。
引导词
1)that
当由陈述句充当宾语从句时，用that引导，that无词义，不充当句子成分，在口语或非正式文体中常省略。
I expect the plane would be diverted.
2)if/whether
当由一般疑问句充当宾语从句时，用if或whether引导，意为“是不是”，不充当句子成分，但不可以省略。
I don't know if/whether he still lives here after so many years.
3)特殊疑问词
假如宾语从句原来是特殊疑问句，仅需用原来的特殊疑问词引导
疑问代词：what, which, who, whom, whose, whatever...
有词义，充当句子成分
We'll do whatever we can to save him.
疑问副词：where, when, how, why...
有词义，充当句子成分
He knows where they live.
Tell us how you are getting on now.
以上三类总结起来就是：
that: 不充当成分，无意义，可以省略;
If/whether: 不充当成分，有意义，不可省略;
疑问代词/副词: 充当成分，有意义，不可省略。
记忆口诀：
陈述句用that，
一般疑问句if或whether，
特殊问句用疑问词。
九种宾语从句不省略that
1)放句首表强调
That he is a good person, we all know.
2)主句的谓语动词与宾语从句之间有插入语
Just then I noticed, for the first time, that he prepared to talk to us.
3)有间接宾语时
Lucy told me that she would not come to school tomorrow.
4)当 it 作形式宾语时
We have made it clear that we will learn to deal with various difficult problems.
5)介词besides、beyond、but、except、in、save 后的宾语从句
The man stood quite still, except that his lips moved slightly.
6)主句中的动词后有 2 个或以上的宾语从句，第二个及未来的 that 不可省
I think it will clear up this afternoon and that they will come to the party.
7)宾语从句本身是一个复合句
He said that if he came back early, he could come for the meeting.
8)当 that 从句单独用来回答问题时
-What did he say at the meeting?
-That the situation was serious.
9)在较为正式或不常见的动词后，如reply, object
He replied that he badly mastered the language.
☆注：以上9种状况考察频率依次递减
if和whether有什么区别
if和whether都可译为"是不是"，在从句中不作句子成分，二者引导宾语从句时一般可以互相替换，口语中多用if代替whether。
1)只可以用whether，不可以用if 引导的宾语从句
①当宾语从句中，紧接or not 时，只用whether ,不然都可。
Let me know whether/if you can come or not.
②当宾语从句提到句首时，只可以用whether ,不可以用if。
Whether it is true, I can't tell.
③whether 可以引导带to 的不定式，而if不可以。
I don't know whether to accept.
④whether 可以放在介词后，做介词的宾语，而if不能。
I worry about whether I hurt her feelings.
⑤若if有歧义，只可以用whether。
Please let me know whether you want to go.
⑥动词discuss, decide, consider, sure等后习惯上也常用Whether引导从句，不需要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.
她是不是能来还是个问题。
The question is whether we can catch the bus.
问题是大家能否赶上公共汽车。
2)只可以用if，不可以用whether 引导的宾语从句
①if引导条件状语从句，意为“假如”
The students will go on a picnic if it is sunny.
②if引导否定定义的宾语从句时
He asked if I didn't come to school yesterday.
③引导状语从句even if和as if时
He talks as if he has known all about it.
总结：
只可以用whether，不可以用if
①当宾语从句中，强调任意选择出现or或紧接or not 时，只用whether，不需要if;
②当宾语从句提到句首时，只可以用whether，不可以用if;
③whether 可以引导带to 的不定式，而if不可以;
④whether 可以放在介词后，做介词的宾语，而if不能;
⑤若if有歧义，只可以用whether。
⑥动词discuss, decide, consider, sure等后习惯上也常用Whether引导从句，不需要if。
⑦引导主语从句和表语从句时宜用whether。
只可以用if，不可以用whether
①if引导条件状语从句，意为“假如”;
②if引导否定定义的宾语从句时;
③引导状语从句even if和as if时。
时态
1)主现从不限。
宾语从句中，假如主句是目前时态，从句的时态依据实质状况来定，不受主句限制。
I know she lives here.
I know she lived here ten years ago.
2)主过从必过。
宾语从句中，假如主句是过去时态，那样从句的时态肯定也是用过去的时态。
She told me that she was 15 last year.
3)客观真理永一现。
假如宾语从句讲述的是某种客观真理，这时，需要用一般目前时。
She told her daughter that the earth is round.
否定转移
1)什么叫宾语从句的否定转移?
就是宾语从句表示否定时，将否定词 not 转移到主句中
举例：“我觉得他不会来” 该如何说呢?
你或许会说：- I think he will not come.
但更地道的表述是：- I don't think he will come.
就是那种我不否定你，我只否定我一个人的感觉。
2)什么时间进行否定转移呢?
进行否定转移一般要满足三个条件：
①主句的主语是第一人称 I 和 we
②主句的谓语动词是表示“觉得”、“相信”、“期望” 等主观想法的词
容易见到：think、believe、suppose、expect、imagine、feel
③主句时态为一般目前时
I don't believe that they can accomplish the task in such a short time.
We don't imagine that they will join the competition.
宾语从句后置
1)什么是宾语从句后置?
就是用一个“it”来代替整个宾语，然后将宾语从句的地方移到句末。
2)那种情况下会出现宾语从句后置?
①“喜、怒、哀、乐”
appreciate, enjoy, like, dislike, love, hate, prefer...
We would appreciate it if you could set up our payment arrangement.
假如你能安排付款，大家会很感激。
②“觉得、发现”
think, make, find, consider, feel, suppose...
He hasn't made it known when he is going to get married.
他还没有宣布他何时结婚。
I consider it wrong to cheat in an examination.
我觉得考试作弊是不对的。
③介词后
answer for, depend on, rely on, insist on, look to, see to, stick to...
You can depend on it that he will finish the job on time.
你可以相信他会按时完成这项工作。
简化宾语从句常用六法
常会遇见把含有宾语从句的复合句转化为简单句，使其与原句意思相同的考试试题。下面就介绍几种常见的简化宾语从句的办法：
1)当主句谓语动词是hope， decide， wish， choose， agree， promise等，且宾语从句的主语与主句主语一致时，宾语从句可简化为不定式结构。
Li Ming hopes he will be back very soon. →Li Ming hopes to be back very soon.
We decided that we would help him. →We decided to help him.
2)当主句谓语动词是know, learn, remember, forget, tell等动词，且主句主语与从句主语一致时，宾语从句可简化为“疑问词+不定式”结构。
She has forgotten how she can open the window. →She has forgotten how to open the window.
注：当主句谓语动词是tell, ask, show, teach等动词，且后带双宾语，从句主语和间接宾语一致时，宾语从句可简化为“疑问词+不定式”结构。
Could you tell me how I can get to the station?→Could you tell me how to get to the station?
3)当主句的谓语动词是order，require等时，假如主句和从句的主语不同，宾语从句可简化为“名词+不定式”结构。
The headmaster ordered that we should start at once. → The headmaster ordered us to start at once.
4)某些动词后的宾语从句，可以用介词加动名词等其他形式简化。
He insisted that he should go with us. →He insisted on going with us.
The poor boy doesn’t know when and where he was born. →The poor boy doesn’t know the time and the place of his birth.
5)某些动词后面的宾语从句可转化为“宾语+V-ing形式”结构。
Liu Ping found that there was a wallet lying on the ground. → Liu Ping found a wallet lying on the ground.
6)动词seem后的宾语从句，也可以用不定式来简化，但句型需要进行适合的变化。
It seemed that the boys were going to win. →The boys seemed to win.
除上述办法外，还有一些特殊句式的转化。
I found that it was difficult to learn English well. →I found it difficult to learn English well.
Soon we found that the ground was covered with thick snow. →Soon we found the ground covered with thick snow.
They found that the box was very heavy. →They found the box very heavy.
宾语从句和状语从句的区别
eg. 1) I will go out tomorrow if it is fine.
2) I don’t know if the train has arrived.
句1中if引导的是状语从句。这个从句表示“条件”，修饰主句。整个句子的意思是：假如明每天气好，我就出去。句2中if引导的是宾语从句，充当谓语动词don't know的宾语。整个句子的意思是：我不了解火车是不是到达。
判断办法：
1)可以从整个句式看。状语从句一般可以放在主句的前面或后面，宾语从句只能放在主句谓语动词之后。
2)从引导词看。if充当宾语从句的连接词时，等于whether， 词义为“是不是”，充当状语从句的连接词时，词义为“假如”。when充当宾语从句的连接词时，意为“什么时间”，充当状语从句的连接词时，意为“当……的时候”。
2)从时态看。if和when作连接词时，引导宾语从句应该注意：从句的谓语动词的时态应依据主句的时态作相应的变化。if和when充当从属连词时，引导条件和时间状语从句，若主句的谓语动词用一般以后时，则从句的时态应用一般目前时表示以后。
—Do you know when he will come back tomorrow ?你了解他明天什么时间回来吗?
—Sorry, I don't know.When he comes back，I'll tell you.对不起，不了解。当他回来了，我将对你说。
—I don't know if he will come.我不了解他会不会来。
—He will come if it doesn't rain.假如不下雨，他会来的。
其他需要说明的问题
1)标点由主句决定，如主句是陈述句、祈使句，则用句号;是疑问句则用问号。
I heard she had been to the Great Wall.
Can you tell me which bus I should take?
2)应该注意个别句子中主从句人称的一致。
3)宾语从句的附加疑问句。
宾语从句的复合句在变成反意疑问句时，假如主句的谓语动词为 think, guess, believe, suppose 等且主语为第一人称时，附加部分要由从句决定;假如主句不是 think 等上述动词或谓语动词是这类词且主语不是第一人称时，附加部分由主句决定。
I think that he is right, isn't he?
I don't believe he is a student, is he?
He supposes that she will come tonight, doesn't he?
He never said he was a good student, did he?
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