名词性从句在句子中起名词作用的各种从句，统称为名词性从句。

根据它们在句中所起的语法作用，这类从句分别称为主语从句、1.作动词的宾语①大部分宾语从句直接跟在动词后：He doesn’t know where the post office is. 他不知道邮局在哪里。

②有些宾语从句前要有间接宾语：He told me what I should read. 他已告诉我应该读些什么。

③如果宾语从句后面有宾语补足语，要使用形式宾语it，而将从句放到补足语后面：I thought it strange that he failed to call me.④在think, believe, suppose, expect等动词之后的宾语从句中，如果从句谓语是否定含义，则不用否定形式，而将主句谓语动词think等变为否定形式：I don’t think you are right.*⑤在think, believe, imagine, suppose, guess, hope 等动词以及I’m afraid等后，可用so代替一个肯定的宾语从句，还可用not代替一个否定的宾语从句：E.g. --- Do you believe it will clear up? 你以为天气会转晴吗？--- I believe so. 我认为会这样。

(--- I don’t believe so./I believe not.) 我认为不会这样。

－Do you think it’s going to rain over the weekend?－.A．I don’t believe B．I don’t believe itC．I believe not so D．I believe not－Don’t you think Jack’s health has been ruined by over drinking?－Yes, he told me himself.A．the thing B．it C．so D．the fact2. 作介词的宾语①that引导的宾语从句只有在except, in, but, besides等少数介词后偶尔可能用到：Your article is all right except that it is too long.你的文章挺好，只是太长了。

Did she say anything about how we should do the work?关于这工作我们该怎么做她说什么没有？*②有时在介词和其宾语从句的中间加形式宾语it;如短语动词answer for（担保）、count on (期待)、depend on、insist on、see to(负责，确保)等后接that引导的宾语从句时，必须冠以形式宾语it。

I’ll see to it that everything is ready. 我将负责把一切准备好。

③介词后的宾语从句不能由if引导，而要用whether.I’m counting on it that you will come.我期待着你的到来。

She’ll see to it that he goes ahead.她将确保他继续进行。

3. 作形容词的宾语在某些形容词（如afra id“恐怕”，sure“确信”，certain“肯定”，confident“相信”等）作表语时，可接一个that引导的宾语从句（也有人认为是状语从句）：I’m afraid (that) I have made a mistake.恐怕我犯了一个错误。

表语从句表语从句放在连系动词（如be, seem, remain等）后：The question is whether we should accept their invitation.问题是我们是否应该接受他们的邀请。

1.when, where, why, because, how 等引导的从句作This is 和That is 的表语时，表示具体的时间、地点、原因、方式等：This is why we put off the meeting. 这就是我们推迟会议的原因。

This is why…＝＞This is the reason why…This is where…＝＞This is the place where…This is when…＝＞This is the time when…This is how…＝＞Thi s is the way(that/in which)…2．主语是reason时，表语从句常用that, 不用because;The reason for his absence was that he was ill。

他缺席的原因是病了。

3．as, as if, because 有时也可引导表语从句；Things were not as they seemed to be.情况并不是看上去的那个样子。

It looks as if it is (或：were) going to rain.看起来天要下雨。

▲注意：as if引导的表语从句有时也可用虚拟语气，表示可能性小。

主语从句主语从句在复合句中作句子的主语。

引导主语从句的词有连词that, whether, 连接代词who, what which; 连接副词when, where, how, why等。

如：1) What is needed for the space trip is careful preparation.2) Whether wild life can be well protected is of great importance.3) Who will go makes no difference.1.主语从句可以直接放在句首；也可用it作形式主语，而将从句放在句末。

如：That light travels in straight lines in known to all.It’s known to all that light travels in straight lines.众所周知，光沿直线运行。

When we shall have our sports meet is still a question.It is still a question when we shall have our sports meet. 我们什么时候开运动会仍然是个问题。

*注意：由that 引导的主语从句大多数要放到句末去。

由what …（所…的东西）引导的主语从句一般不用it 作形式主 语的结构：误：It is a book what he wants.正：What he wants is a book. 他要的东西是一本书。

由whether 及其它连词引导的主语从句放在句首或句子后部皆可。

由带主语从句的句子是疑问式，则须用it 作形式主语结构。

如：Has it been announced when the planes are to take off?飞机什么时候起飞宣布了没有？2．常见的用it 作形式主语的复合句结构： ①It is ＋名词＋that 从句It is a fact (a shame, a pity, no wonder, good news …) ②It is ＋形容词＋that 从句It is necessary (strange, important, wonderful, possible, likely,…) that … 这类主语从句中，谓语动词多数为“（should ）＋动词原形” ③It is ＋过去分词＋that 从句It is said (reported, decided, …) that …④It ＋不及物动词＋that 从句:It seems (happened, doesn’t matter, has turned out,…) that … △主语从句的连词that 虽不作成分，但亦不省略。

△whether 引导主语从句时，不用if 。

△单个从句作主语时，谓语动词用单数。

同 位 语 从 句在主从复合句中，用作同位语的从句，叫同位语从句。

它一般跟在某些名词（如fact, idea, news, promise, hope, order, doubt, bet 等）的后面；用以说明或解释前面的名词，引导同位语从句的词有连词that, whether, 连接副词how, when, where, why 等。

如：1）We were very excited at the news that our team had won.2）The fact that women can work as well as men is clear.3）Henry Adams made a promise that he would not open it until 2 o’clock. 4）I have no idea when Chaplin’s film will be on again. △同位语从句的连词不可省略。

△同位语从句与其前面的名词之间是同位关系, 这一名词在从句中不充当任何成分。

△同位语从句有时被别的词把它和名词隔开。

如：The story goes that he killed the cruel king with an arrow.同位语从句和定语从句的区别①从意义上讲，前者对名词加以补充说明，后者对名词进行修饰和限定。

②从结构上讲，前者由连接词引导，后者由关系词引导。

③从内涵上讲，前者所说明的名词与从句没有逻辑关系，后者所限定的名词是其逻辑上的主语、宾语、表语、定语、状语等。

The news that they won the match is true. 他们比赛获胜的消息是真的。

[同位语从句，news 和从句没有逻辑关系]The news that you told us yesterday is true.你昨天给我讲的消息是真的。

[定语从句，news 是told 的逻辑宾语]The order when we should return hasn’t reached us.我们什么时候该返回的命令还未到。

[同位语从句,order 和从句没有逻辑关系]The day when New China was founded will never be forgotten. 新中国成立的那天永远不会被忘记。

[定语从句，day 是founded 的逻辑状语]④引导同位语从句的连接词不可省略，而引导定语从句的关系词作宾语时常可省略。