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名词性从句是在句子中起名词作用的句子。 名词性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、表语、同位语、介词宾语等，因此根据它在句中不同的语法功能，名词性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。
主语从句(subject clause)
主语从句（subject clause）,顾名思义就是利用一个从句来代替主语。
例如：That he finished writing the composition in such a short time surprised us .
这句话的结构就是最基础的：主＋谓＋宾
主语：That he finished writing the composition in such a short time
谓语：Surprised
宾语：us
宾语从句（object clause）
名词性从句均是异曲同工。即宾语从句就是利用一个从句来代替宾语。
例如：I think (that) you shoud tell the truth
主语：I
谓语：think
宾语：（that）you should tell the truth
表语从句（Predicative Clause）
名词性从句均是异曲同工。即表语从句就是利用一个从句来代替表语。
众所周知，表语谓语系动词（be 动词及感官动词）之后，所以一般结构为主语+系动词+表语从句
例如：the trouble is that he has lost a lot of money.
主语：the trouble
谓语: is
表语: that he has lost a lot of money.
同位语从句（appositive Clause）
我知道大家对同位语会比较陌生，同位语，按字面意思理解，就是与同位语前面的那个名词具有相同地位的成分. 即同位语通常紧跟在名词、代词后面,进一步说明、解释它的情况
例如 :
He my brother is a superstar.
他，即我的哥哥，是个明星(my brother是he的同位语)
We both can do it.
我们，两个人，都可以做(both就是we的同位语)
Where is you classmate tom
你的同学汤姆在哪里（tom 是classmate的同位语）
同位语从句，就是用一个句子来做同位语成分，通常跟在一些特定的名词之后。这些名词有：
hope/wish/fact/answer/problem/news/belief/idea/promise/suggestion/order/conclusion/information/thought
这些名词的名义都很抽象，指代不明确，所以往往跟一个同位语从句来解释这些名词的具体内涵。比如：
The fact that she didn't like me really hurts me.
主语：The fact
谓语： really hurts
同位语：that she didn't like me
宾语：me
wuyan841106
在复合句中起名词作用的从句叫名词性从句(Noun Clauses).名词性从句的功能相当于名词或名词词组, 它在复合句中能担任主语、宾语、表语、同位语、介词宾语等,因此根据它在句中不同的语法功能,名词性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. 名词性从句在功能上相当于名词 His job is important. 主语｛ What he does is important. This is his job. 表语｛ This is what he does every day. I don’t like his job. 宾语｛ I don’t like what he does every day. I don’t know about the man, Mr. White. 同位语｛ I don’t know about the fact that he is a teacher. Subject Clause(主语从句) 1 That he will succeed is certain. 2 Whether he will go there is not known. 3 What he said is not true. 4 Where he hid the money is to be found out . 5 Whoever comes is welcome. 6 How we can help the twins will be discussed at the meeting. 7 When they’ll start the project has not been decided yet. 形式主语 “It” is used as empty subject. 为避免主语冗长,句子头重脚轻,经常用it作形式主语,主语从句放在后面作真正的主语. 1. It is certain that he will succeed. 2. It is not known whether he will go there. 3. It has not been decided yet when they’ll start the project. 在下列句型中常使用that引导主语从句： It’s likely / possible / important / necessary / clear that… 很可能/重要的是……/必要的是……/很清楚…… It’s said / reported that… 据说/据报道…… It seems / appears / happens that… 似乎/好像/碰巧. It’s been announced / declared that… 已经通知/宣布…… It’s no wonder that… 并不奇怪/无疑…… It’s a pity / a fact / common knowledge (众所周知)/ a common saying (俗话说) that… It’s likely / possible / important / necessary / clear that… 很可能/重要的是……/必要的是……/很清楚…… It’s said / reported that… 据说/据报道…… It seems / appears / happens that… 似乎/好像/碰巧. It’s been announced / declared that… 已经通知/宣布…… It’s no wonder that… 并不奇怪/无疑…… It’s a pity / a fact / common knowledge (众所周知)/ a common saying (俗话说) that… 引导名词性从句的关联词： I don’t doubt (that) you will succeed. I don’t know whether/if he will come tonight. I doubt if /whether you will keep your promise. 3个句子中的连词that, whether, if (是否)在名词性从句中只起连接作用,在句中不担任成分,被称为连接词. 注意: A. that 本身无意义,在宾语从句中可以省略,但在别的三种名词性从句中不可以省略.B. whether 和if有是否的意义,在宾语从句中二者通常可以互换.但whether 可以用于所有的四种名词性从句,而if 仅可以用于宾语从句. 名词性从句： 一、名词性从句的语序 (1) 名词性从句构成有两种 a. That + 陈述句 That light travels in straight lines is known to all. b. 疑问词+句子的剩余成分 This is what we are looking for. (2) 疑问词引导的名词性从句要求使用陈述 句语序,不能用一般疑问句语序. 他是怎么成功的仍然是个谜. How was he successful is still a puzzle. ( F )\x0b How he was successful is still a puzzle. ( T ) 你能告诉我他住在什么地方吗? Could you tell me where he lives? ( T )\x0bCould you tell me where does he live? ( F ) 二、名词性从句连接词的选用： (1) that 和what 的选用 that 和 what 都可引导所有的名词性从句.但是,what除起连接作用外,还在名词性从句中充当成分,可作从句的主语、宾语、或表语.而that在名词性从句中不充当任何成分,只起连接作用. （2）if 和whether的选用： 不能使用if 的情况: a. 主语从句\x0b b. 表语从句\x0b c. 同位语从句\x0b d. 介词后的宾语从句\x0b e. whether to do 做动词宾语不能用if to do.\x0b f. 与 or not 连在一起引导宾语从句时不用if. 其它连接代词和副词的使用： 主要根据名词性从句中的具体意义,正确的选择 who, which, when, where, why, how 等连接词,这些连接词既具有疑问含义,又起连接作用,同时在从句中充当各种成分.
