名词性从句
在主从复合句中，从句可以充当主句的主语、表语、宾语或同位语。由于在多数情况下，主语、表语、宾语或同位语这四种句子成分由名词性词类充当，所以，我们把这些作用相当于名词的从句统称为名词性从句，把充当主语、表语、宾语或同位语的从句分别称为主语从句、表语从句、宾语从句或同位语从句。也就是说充当什么成分就叫什么从句。名词性从句由连接词（或关联词）引导。
常用的连接词有：
疑问词（who, whom, whose, what, which, where, why, when, how）可以引导主语、宾语和表语从句。
它们的特点是：1、疑问词有本身的词义；2、疑问词在从句中担当句子成分，如主语、宾语或状语；3、这种疑问词引导的从句一律用陈述语序，不能用疑问语序。
For example:
Do you know whom they are looking for? 你知道他们在找谁吗？（宾语从句，陈述语序。不能是whom are they looking for?）
I don’t know who did it. 我不知道这是谁干的。（宾语从句。在从句中如果疑问词作主语，其陈述语序和疑问语序一致。）
She asked me where I had been. 她问我到哪儿去了。（宾语从句。陈述语序，不能是where had I been. 直接引语，间接引语。注意这句话的时态。）
Can you tell me when the train will arrive? 你能告诉我火车什么时候到吗？(宾语从句。陈述语序，不能是when will the train arrive. 直接引语，间接引语。)
I don’t know why he hasn’t come yet. 我不知道他为什么还没来。（宾语从句，陈述语序。不能是why hasn’t he come yet.）
He didn’t tell me what you were doing. 他没和我说你在干什么。（宾语从句，陈述语序。不能是what were you doing.）
What you have done might do harm t other people. 你所做过的事情有可能伤害别人。（主语从句。what 作从句的宾语。陈述语序，不能是what have you done. 如果用疑问语序，意思发生了变化，成了“你做了什么？”。）
I don’t know where he is now. 我不知道他现在在哪里。（宾语从句，陈述语序。不能是where is he now.）
Where he went for his weekend is not known. 不知道他去哪里过的周末。（主语从句，where 作从句的地点状语。陈述语序，不能是where did he go for his weekend.）
Whose fault this is is not important. 这是谁的过错并不重要。（主语从句，whose 作从句的定语。陈述语序，不能是whose fault is this.）
What I want to know is where he has gone for his weekend. 我想知道的是他到哪里度周末去了。（这句话包含两个名词性从句：what I want to know是主语从句，what 在从句中作宾语，从句用陈述语序，不能是What do I want to know. Where he has gone for his weekend 是表语从句，where 在从句中作状语，从句用陈述语序，不能是where has he gone for his weekend.）
下面我们再分别讲述主语从句、宾语从句、同位语从句和表语从句。
主语从句
1．that 引导主语从句时，that 没有意义，但不能省略。（that 引导宾语从句时可以省略。）
For example:
It worried her a bit that her hair was turning gray. 她的头发正在变白，这使她很不安。that引导主语从句，it 作形式主语，that 不能省略。
That she is a rich woman is known to us all. 众所周知，她是个富有的女人。这是that 引导主语从句，that 不能省略。这句话可以改为用it 作形式主语的句型。请同学们改写：It is known to us all that she is a rich woman.）
We didn’t know (that) you had sold your house. 我们不知道你已经把你的房子卖了。这是that引导宾语从句，that 可以省略。注意这句话的时态。
2．从句作主语时，多数情况下由 it 作形式主语，而把主语从句放在后面，尤其是谓语部分（包括宾语）较短的情况下。
For example:
It wasn’t very clear what she meant. 不清楚她是什么意思。
It is important that he should come on time. 他按时来是很重要的。
It is true that that man on the left is a well-known writer here. 左边那个人是本地的一位著名作家，这是真的。这里，第一个that 引导主语从句，是单纯的连词，无词义，不作句子成分。第二个that 是指示代词，作句子成分，是man 的定语。
3．whether 既可以引导主语从句也可以引导宾语从句，但if不能引导主语从句。whether 后面可以加or not, 而if 不能与or not 连用。作介词宾语时不用if.
For example:
Whether I knew John doesn’t matter. = It doesn’t matter whether I knew John. 我是否认识约翰没有关系。
Whether or not she’ll come isn’t clear. = Whether she’ll come or not isn’t clear. = It isn’t clear whether …. 她是否来还不清楚。
It all depends on whether we can get their cooperation. 这是主语从句还是宾语从句？it 是形式主语吗？it 是代词，whether 引导的是宾语从句，作介词on 的宾语，不能用if引导。请翻译这句话。这完全取决于我们是否能得到他们的合作。
I worry about whether I hurt her feelings. 宾语从句，介词宾语，不能用if 引导。请翻译这句话。
She asked me whether/if you were married. 宾语从句，既可以用whether, 又可以用if 引导。注意时态的对应。请翻译这句话。
We haven’t decided whether/if we shall give them aid.
I’m not sure whether/if the report is believable.
Now let’s do some translation:
现在还很难预测谁会赢得下一届总统选举。
It is still hard to predict who will win the next presidential election.
对于多数公民来说，谁当选总统无关紧要。
Who will become the president doesn’t matter much to most citizens.
这位前总统是否会被判处死刑还有待观察。
It remains to be seen whether the ex-president will be sentenced to death.
真可惜，王教授不能出席我们的英语晚会。
It is a pity that Prof. Wang can’t attend our English Evening.
我们需要的是更多的时间。
What we need is more time.
宾语从句
在谓语动词、介词、动词不定式、分词、动名词之后都可以带有宾语从句。某些形容词如sure, happy, glad, certain, pleased 等之后也可以带有宾语从句。
1．that 引导的宾语从句: that 没有意义，在口语或非正式文体中常省略：如：
I really feel she’s making a mistake. 我的确感到她正犯错误。
James said (that) he was feeling better. 詹姆斯说他感到好些了。
Hearing that his son was badly wounded, he hurried to the hospital to see him. 听说儿子受了重伤，他急忙赶到医院去看望他。
I suggested that we should go home. 我建议我们回家去。虚拟语气，that 一般不能省略。
2．whether/if (是否)引导的宾语从句：如果要突出“究竟是…还是不…”，常在whether 后面加or not; if 一般不与or not连用。如：
He asked me if/whether I knew John. 他问我是否认识约翰。
Let me know whether you can come or not. 你能来还是不能来，告诉我一声。
3．在think, believe, suppose, expect 等动词的宾语从句中，否定不用在从句中，而是将think 等词变为否定形式。
For example:
I don’t think the film is interesting. 我觉得这部电影没什么意思。
I don’t suppose we are going outing tomorrow. 我认为我们明天不会出去郊游。
4．如果从句作宾语而后面还有补语，为了保持句子的平衡，用it 作形式宾语，而将宾语从句放在句尾。常跟这样的复合宾语的动词有：make, find, see, hear, feel, think, consider, regard, take….for granted等。如：
George made it clear that he opposed this project. 乔治已明确表示他反对这个项目。it 代表that 引导的句子，作宾语，clear 是宾语补足语。
They kept it quiet that he was dead. 对他已经死亡的消息，他们秘而不宣。
I took it for granted that you’d stay with us. 我想当然认为你会和我们呆在一起。
同位语从句
同位语从句是对名词的内容给予具体、详细的说明。常在后面接同位语从句的名词有fact, news, idea, truth, hope, suggestion, question, problem, doubt, fear, belief等。同位语从句常用的引导词为that,有是也用when, where 等疑问词。如：
The news that the United States was hit by terrorist attacks took the whole world by surprise. 美国受到恐怖主义分子袭击的消息令全世界吃惊。
The idea that you can do this work well without thinking is quite wrong. 你认为不动脑筋就能做好这件工作的想法是完全错误的。
People used to hold the belief that the earth was the center of the universe. 人们曾认为地球是宇宙的中心。
The difficulty lies in the fact that we are short of money. 困难在于我们缺乏资金这个事实。
They have no idea at all where he has gone. 他们一点儿也不知道他去哪儿了。
注意：同位语从句的that 只是引导词，没有其他语法作用，在句子中不作句子成分，不能省略；而定语从句中的that 除了引导定语从句外，还是定语从句的一个成分，在定语从句中作主语或宾语，作主语时不能省略，作宾语时可以省略。如：
The idea that some peoples are superior to others is sheer nonsense. 有些民族优越于其他民族这种想法简直荒谬。（请辨别是同位语从句还是定语从句。）（同位语从句）
The idea that he proposed at the meeting is sheer nonsense. 他在会议上提出的这个想法简直荒谬。（请辨别是同位语从句还是定语从句。）（定语从句）
No one is happy with the fact that he found out. 没有人对他发现的事实感到高兴。（请辨别是同位语从句还是定语从句。）（定语从句）
No one is happy with the fact that he will become their boss. 没有人对他将成为他们的老板这一事实感到高兴。（请辨别是同位语从句还是定语从句。）（同位语从句）
表语从句
表语从句位于主句的连系动词之后，在非正式文体中引导词that可以省略。如：
That’s not what I want. 那不是我要的。
That’s why I have come. 那就是我为什么来了。
My opinion is that things will improve. 我的意见是事情会好起来的。
One advantage of solar energy is that it will never run out. 太阳能的一个优点是永远也不会枯竭。
The truth is that he didn’t really try. 实际情况是他没有真正努力。
The problem is who is to pay and when we can start. 问题是谁来付帐、我们又何时开始。
The fact is that he didn’t notice the car until too late. 事实是他注意到车时已经太晚了。
What surprised me was that he spoke English so well. 使我感到吃惊的是他英语讲得那么好。
All I can say is that I have nothing to do with it. 我能说的就是我与此事没有关系。
What I want to know is where we shall go and whether she will join us. 我想知道的是我们要去什么地方以及她是否加入我们。
表语从句位于主句的连系动词之后，在非正式文体中引导词that可以省略。如：
The fact is that he didn’t notice the car until too late. 事实是他注意到车时已经太晚了。
What surprised me was that he spoke English so well. 使我感到吃惊的是他英语讲得那么好。
All I can say is that I have nothing to do with it. 我能说的就是我与此事没有关系。
What I want to know is where we shall go and whether she will join us. 我想知道的是我们要去什么地方以及她是否加入我们。
此外，表语从句还可由as if （好像）引导。如：
It looked as if it was/were going to rain. （虚拟语气）
Now let’s do some translation:
这就是她昨天请一天假的原因。
That is why she had a day off yesterday.
我的想法是，个人的权利应该得到充分尊重。
My idea is that individual rights should be fully respected.
问题在于上帝是否真的存在。
The question is whether the God really exists.
我想知道的是，他是如何在这么短的时间内完成这个项目的。
What I want to know is how he managed to complete the project in such a short time.
形容词后的that 从句
that 引导的名词性从句还可以用在一些形容词后面。这种句型一般都用人作主语，所用的形容词都是表示思想状况或感情色彩的形容词，如certain, sure, positive, afraid, convinced, anxious, disappointed, worried, glad, happy, sorry, amazed, surprised, aware, doubtful, confident等等。如：
I am sure/certain that he’s at home now. 我肯定他现在在家。
He became angry that you made the same mistake. 你犯了同样的错误，他生气了。
He remains confident that he will win. 他仍然自信他会赢
She is aware that I can’t help her. 她知道我帮不了她的忙。
I am glad that you’ve come. 你来了我很高兴。
He appeared/seemed surprised that I said “no”. 我说不，他似乎很吃惊。
I am afraid that I can’t promise you anything. 恐怕我不能向你保证什么。
We were rather disappointed that you were not able to come yesterday. 昨天你没能来我们有点失望。
I am a bit worried that she will not be able to make it. 我有点担心她做不成这件事情。