名词性从句名词性从句（主语、表语、宾语、同位语从句）（一）主语从句1．定义：用作主语的从句叫做主语从句。
2．构成：关联词+简单句3．引导主语从句的关联词有三类：(1) 从属连词that。
如：That they were in truth sisters was clear from the facial resemblance between them.很明显，她们确是亲姐妹，她们的脸型很相似。
(2) 从属连词whether。
如：Whether he’ll come here isn’t clear. 他是否会来这里还不清楚。
(3) 连接代词who, whom, whose, what, which, whoever, whatever, whichever连接副词where, when, how, why。
如：What she did is not yet known. 她干了什么尚不清楚。
解释：1．主语从句能用it作形式上的主语。
常以it作形式主语的句型有：A. It+be+形容词(obvious, true, natural, surprising, good, wonderful, funny, possible, likely, certain, probable, etc.)+that从句。
如：It is certain that she will do well in her exam. 毫无疑问她考试成绩会很好。
B. It+be+名词词组(no wonder, an honour, a good thing, a pity, no surprise, etc.)+that从句。
如：It’s a pity that we can’t go. 很遗憾我们不能去。
C.It+seem, happen等不及物动词及短语+that从句。
如：It seems that Alice is not coming to the party at all. Alice似乎不来参加晚会。
D.It+doesn’t matter (makes no difference, etc.)+连接代词或连接副词引起的主语从句。
如：It doesn’t matter whether she will come or not. 她是否来这无关紧要。
F. 当that引导的主语从句出现在疑问句中时，要以it作形式主语，而把主语从句后置。
如：Does it matter much that they will not come tomorrow? 他们明天不来很要紧吗？G. 当主语从句出现在感叹句中时，要以it作形式主语，而把主语从句后置。
如：How strange it is that the children are so quiet! 孩子们这么安静真奇怪！2．注意连接代词whoever, whatever, whichever等引导主语从句的含义Whoever comes will be welcome. (whoever=the person who) 来的人将受到欢迎。
（二）表语从句1．定义：用作表语的从句叫做表语从句。
2．构成：关联词+简单句3．引导表语从句的关联词的种类：(1) 从属连词that。
如：The trouble is that I have lost his address. 麻烦是我把他的地址丢了。
(2) 从属连词whether, as, as if。
如：He looked just as he had looked ten years before. 他看起来还与十年前一样。
注：从属连词if一般不用来引导表语从句，但as if却可引导表语从句能跟表语从句的谓语动词一般为系动词be, seem, look等。
如：It looked as if it was going to rain. 看起来天要下雨了。
(3)连接代词who, whom, whose, what, which, whoever, whatever, whichever连接副词 where, when, how, why。
如： The question is how he did it. 问题是他是如何做此事的。
解释：1．连词because可引导表语从句。
如：I think it is because you are doing too much. 我想这是因为你做得太多。
2．在一些表示“建议、劝说、命令”的名词后面的表语从句中，谓语动词用虚拟语气。
should+动词原形表示，should可省略。
如：My suggestion is that we (should) start early tomorrow. 我的建议是我们明天一早就出发。
注意：1．what引导●“…….+ ，= “…….+ is + ，表示“.….是表语从句”例：Raw material is what we are badly in need of.= Raw material is the thing that we are badly in need of.2．when、where、why、whether、how引导●“…….+ is +when、where、why、whether、how表语从句”，表示“.….是表语从句”例：That’s where we differ.●表语从句中只能用whether表示是否例：The question is whether we can finish our work by tomorrow morning.3．that引导●“…….+ is /remain/look/seem/appear + that表语从句”，表示“.….是表语从句”例：What’s troubling me is that I don’t have much experience in this field.●主语是reason时，表语从句必须由that引出例：The reason I don’t go there was that I got a new job.4．as if/as through引导●“……look/seem/appear/remain（系动词）+ as if/as through 表语从句”，表示“.….好像表语从句”例：It looks as if it is going to rain.（三）宾语从句1．定义：用作宾语的从句叫宾语从句。
2．构成：关联词+简单句3．引导宾语从句的关联词有三类：(1) 从属连词that。
如：He told us that he felt ill. 他对我们说他感到不舒服。
注：that在引导宾语从句时也并不是任何情况下都可以省略。
在以下情况下，that不能省略。
1．Everybody could see what happened and that Tom was frightened.(and连接两个宾语从句，that 宾语从句放在and的后面时，that不能省略。
)大家都会看出发生的事情并知道Tom非常害怕。
2．I know nothing about him except that he is from the south.(that引导的宾语从句作介词宾语时，that不能省略。
)对他我一无所知，只知道他是南方人。
3．That he ever said such a thing I simply don’t believe. (that从句位于句首时，that不可省略。
) 我简直不相信他曾说过这样的话。
4．We decided, in view of his special circumstances, that we would admit him for a probationary period. (主句谓语动词与that从句之间有插入语，that不可省略。
)鉴于他的特殊情况，我们决定应允他一段试用期。
(2)从属连词if/whether。
如：I doubt whether he will succeed. 我怀疑他是否会成功。
(3)连接代词who, whom, whose, what, which, whoever, whatever, whichever连接副词where, when, how, why。
如：Who or what he was, Martin never learned.(1) 介词宾语从句宾语从句也可用作介词的宾语。
如：He was deeply displeased by what had occurred that day.他对那天发生的事感到很不快。
I walked over to where she sat. 我走向她坐的地方。
有时介词可以省略。
如：I don’t care (for) who marries him. 我不管谁跟他结婚。
解释：1．如果宾语从句后还有宾语补足语，则用it作形式宾语，而将宾语从句后置。
如：We thought it strange that Xiao Wang did not come yesterday.我们认为小王昨天没来是奇怪的。
He has made it clear that he will not give in.他已表明他不会屈服。
2．作介词的宾语：连词that引导的名词性从句很少作介词的宾语，只用在except, but, in后。
其他一些介词的宾语从句如果由连词that引导，则需用it先行一步，作形式宾语。
如：He is a good student except that he is careless.他是一个好学生，只是有点粗心。
You may rely on it that I shall help you. 你可以指望我会帮助你的。
介词宾语不可以用which来引导，而要用what来引导。
如：Are you sorry for what you've done?你为你所做的一切感到内疚吗？3．某些形容词或过去分词后常接宾语从句，这类形容词或过去分词有sure, glad, certain, pleased, happy, afraid, surprised, satisfied等，连词that可省略。
如：I am not sure what I ought to do.我不能确定我该做什么。
4．连词whether (…or not)或if引导的宾语从句if和whether引导的宾语从句可以互换使用，但whether常和or not连用，if一般不与or not 连用。