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高三语法复习三：名词性从句
定义：在句子中起名词作用的句子叫名词从句 (Noun Clauses)。名词从句的功能相当于名词词组，它在复合句中能担任主语、宾语(动词宾语或介词宾语)、表语、同位语等，因此，根据它在句中不同的语法功能，名词从句又可分别称为主语从句、宾语从句、表语从句和同位语从句。
I.引导名词性从句的连接词
引导名词性从句的连接词可分为三类：
连词： that (无任何词意),whether,if (均表示“是否”表明从句内容的不确定性), as if,as though (均表示“好像”,“似乎”;用于引导表语从句)
连接代词： what, whatever, who, whoever, whom, whomever whose, which, whichever
连接副词： when, where, how, why
一、主语从句
1. 作句子主语的从句叫主语从句。主语从句通常由从属连词 that,whether,和连接代词 what,who, which, whatever,whoever 以及连接副词 how,when,where,why等词引导。that在句中无词义，只起连接作用，主语从句中that不能省略；连接代词和连接副词 在句中既保留自己的疑问含义、又起连接作用，在从句中充当从句的成分。
Eg:That he will succeed is certain.
What he wants to tell us is not clear.
It is known to us how he became a writer.
2.有时为避免句子头重脚轻，常用形式主语it 代替主语从句作形式主语放于句首，而把主语从句置于句末。主语从句后的谓语动词一般用单数形式。常用句型如下：
(1) It is +名词+ 从句
It is a fact that ... 事实是... It is an honor that .…非常荣幸
It is common knowledge that …是常识 It’s a pity that... 很遗憾，很可惜
Eg:It is an honor that I could deliver a lecture on the current market trend.
(2) It is +形 容 词 + 从 句
It is natural that... 很自然… It is strange that... 奇怪的是
其他词如important, necessary...等.
Eg:It is strange that I like to do my homework.
(3)It is +不及物动词+从句
It seems that.. 似乎.. It happened that.. 碰巧... It appears that … 似乎..
Eg:It seems that he is not quite himself today.他似乎今天不太对劲儿。
(4)It +过去分词+从句
It is reported that.. 据报道 .It has been proved that...已证实. It is said that..据说...
It is estimated that...据估计 It is believed that...人们相信
Eg:It is said that practice makes perfect.
3.What的重要考点
1)当名从本身缺主、宾、表且指物时，翻译成“所 …… 的”(常考单词achieve, speak,do,say,
discuss)
eg: What we discussed most was staying united to combat the pandemic.
我们谈论最多的就是团结一致，共同抗疫。
2)what+n. 位于名从之首，回归本意"什么"eg:I wonder what book he likes best.
3)What+adj+n. 位于名从之首表感叹 eg:He realised what great difficulty he was facing.
4. is known to us that light goes faster than sound.
is known to us is that light goes faster than sound.
is known to us, light goes faster than sound.
A. What B.It C.Which D.As
二、 宾语从句
名词句用作宾语的从句叫宾语从句。引导宾语从句的关联词与引导主语从句，表语从句的关联词大致一样，在句中可以作谓语动词或介词的宾语。
注意句子语序要用陈述语序。
Eg:I want to know what he has told you.我想知道他告诉了你什么
She always thinks of how she can work well.她总是在想怎样能把工作做好。
She will give whoever needs help a warm support. 凡需要帮助的人，她都会给予热情的支持。
2.主从复合句的时态原则
当主句动词是现在时，从句根据自身的句子情况，而使用不同时态。
Eg:Tom tells us that he studies English every day. (从句用一般现在时)
Tom tells us that he studied English last term. (从句用一般过去时)
I know (that) he will study English next year. (从句用一般将来时)
当主句动词是过去时态，从句则要用相应的过去时态，如一般过去时，过去进行时，过去将来时等；
Eg:The teacher told us that Tom had left us for America.
当从句表示的是客观真理，科学原理，自然现象，则从句仍用现在时态。例如： He said that the earth moves around the sun.
否定前移：think, believe, imagine,suppose 等等动词引起的否定性宾语从句中，要把上述主句中的动词变为否定式。
Eg:We don't think you are here.我们认为你不在这。
I don't believe he will do so.我相信他不会这样做。
注意，此类句式变成反义疑问句，遵从“一从，二三主”的原则
3.it 作形式宾语
常做下列动词的形式宾语think,find, consider, believe,feel, make
结构： v.+it+ 形容词 (necessary,important, natural, useful, worthwhile)/名词+that ...
Eg: I think it important that you should attend the meeting.
此外hate,love, dislike, appreciate, depend on, see to(保证，确保完成)后常用it做形式宾语
结构：v+it+that 引导的宾语从句
Eg: I hate it that she talked to me in this way.
2 .名词性从句中只用whether，不用if的情况
1)介词后只能用 whether
2 ) 与 or not 连用时只能用 whether
3)后接动词不定式只能用 whether引导
5)引导主语从句并在句首时
6)引导表语从句时
Whether there is life on the moon is an interesting question.月球上有没有生命是个有趣的问题。
The question is whether she should have a low opinion of the test
Everything depends on whether we have enough money.一切要看我们是否有足够的钱。
I wonder whether he will come or not.我想知道他来还是不来。
Can you tell me whether to go or to stay 你能否告诉我是去还是留
三、表语从句 (结构：主语+系动词+表语从句)
系动词：
1.be 动词
2.感官动词： look, sound,smell, taste, feel
3.表示“变”与“不变”的词： become,get, turn, grow(变得); keep, hold, stay, remain.
Eg: The clouds are gathering. It looks as if it is going to rain.
考点：
从属连词 whether, that
引导词 连接代词 what,which, who, whom, whose
连接副词 when, where, why, how,as if/though, because
Eg: The question is not whether he is honest.
注意点：
1. as if/though 引导的表语从句可以用虚拟语气/陈述语序
Eg: The elephant feels as if it were a wall.(虚拟语气)
The clouds are gathering. It looks as if it is going to rain.(陈述语序)
2.because,通常用于 this/that/it is/was because.….… 句型
Eg: That was because I was ill.
3.主句主语是 reason,cause 时，用 that 引导而不是because
Eg: The reason why he speaks English well is that he is a native speaker.
四、 同位语从句
1、概念
当引导词为evidence、thought、advice、demand、doubt、fact、hope、idea、information、 message、news 、order、problem、promise 、question、request、suggestion、truth、wish、words（消息）时，后面的从句通常对前面的名词起补充解释作用，两者之间是同位关系，叫做同位语从句；
It is a fact that he has done his best.
Words came that the meeting has been postponed to next week.
2、与定语从句的区别
定语从句是起修饰或限制作用，而同位语从句起补充说明的作用。
The fact that you are talking about is important.
The fact that he had not said anything surprised everybody.

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