本博文源于《语法知识清单》。所谓的名词性从句就是指句子作名词。名词可以充当那些成分，主语、宾语、表语、同位语。因此就诞生了主语从句、宾语从句、表语从句、同位语从句。
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：从属连词、连接代词、连接副词。
从属连词
that/whether/if 在从句中不充当任何成分，只起连接从句的功能。that没有实际意义，而whether/if有“是否”的意义。
- That we need more equipement is obvious.
只能用whether的情况：
- whether引导的主语从句（位于句首）、表语从句或同位语从句时
- whether引导的从句作介词宾语时
- 后紧跟不定式时
- 后紧跟or not时
- 位于discuss后引导宾语从句时
连接代词
连接代词指具有代词的特点，同时又能引导从句的词，主要有what,whatever,who,whoever,whom,whose,which,whichever等。这些词在从句中既作特定的成分，又有具体的含义，不能省略。
- Whoever breaks the law will be punished.
连接副词
连接副词指具有副词的特点，同时又能引导从句的词，主要有when,where,how,why,whenever,wherever等。这些词在从句中既作状语，又有具体的含义，不能省略
- Sometimes,how we show our gratitude to person is reflected in the knid of food we serve him or her.(how引导主语从句，且在从句中作方式状语)
主语从句
在句中起主语作用的从句称为主语从句。引导主语从句的连接词主要有：从属连词、连接代词和连接副词。
that引导的主语从句
that置于句首的主语从句(that在从句中不作任何成份，也没有含义，只起连接作用，不能省略)
- That the college will take in more new students is true.
that从句作主语时，常用it作形式主语，that引导真正的主语从句后置，常见的句式主要有如下几种：
- It + 系动词 + 形容词 + that从句
- It + 系动词+ 名词 + that从句
- It + be + 过去分词 + that从句
- It +动词 （+宾语或状语） + that 从句
例子：
It is obvious that you’ve made a big mistake.
It is a pity that you didn’t attend the lecture yeterday.
It is reported that no passengers were injured in the accident.
It turns out that our team has won the game.
whether,if引导的主语从句
whether引导的主语从句既可以放在句首，也可以放在句末，但if引导的主语从句只能放在句末，前面需用it作形式主语。whether，if在从句中不作任何成份，只起连接作用，不能省略，表示“是否”
- It is unknown whether/if he has agreed to my plan.
wh-类连接词引导的主语从句
wh-类连接词包括连接代词(who,whom,whose,what,whomever,whatever等)和连接副词(when,where,how,why,whenever,wherever,however)有时可用it做形式主语
- It makes no difference where we shall have the meeting.
what引导主语从句时，谓语动词的单复数形式遵循意义一致原则
- What the kind wanted was only a new schoolbag.
宾语从句
宾语从句的分类
动词的宾语从句
- I can’t see how he bought such an expensive car.
介词后的宾语从句
- Martha is always thinking of how she can do more for others.
形容词后的宾语从句
- I’m very pleased that all of your family will come.
表语从句
表语从句的连接词
从属连词that和whether
在从句中不作成分，that无词义，一般不省略；whether有“是否”之意，不能换成if。
- The reason for your mistake is that you lack confidence.
连接代词
who,whom,whose,what,which,whoever,whomever,whatever,whichever等
- This place isn’t what is used to be.
连接副词
when、where、why、how、whenever、wherever、however
- Why not try your luck downtown?That’s where the best jobs are.
其他连接词
because、as if 、as though。
- It sounds as if you are from the south of the United States.
表语从句需要注意的问题
主语为名词reason时,表语从句中的连接词要用that,不用because,构成句型"The reason(why…) is that…".
- The reason is that you haven’t been well prepared for what’s going to happen.
表语从句的虚拟语气
如果主句的主语是advice,proposal,recommendation,suggestion,order,command等名词时，表语从句的谓语应用虚拟语气，即无论主语是单数或复数，谓语一律用"(should+)动词原形"的形式
- The proposal of the UN is that a peace-keeping force (should ) be sent to the area.联合国的建议是向这个地区派驻维和部队。
同位语从句
同位语从句是以解释说明某一名词内容和实质的从句。
可跟同位语从句的名词
不是所有名词可以跟同位语从句。
同位语从句的连接词
常用的连接词有：that，whether，why，who，where，how，when等.if一般不连接同位语从句。that，whether不作成分，whether表示“是否”，其他连接词具有实义，同时在同位语从句中做一定成分。同位语从句的引导词一般都不省略。
- The report that he was going to resign was false.
同位语从句的语气
在suggestion,advice,request,order,demand,requirement等意为“建议，命令，要求”的名词后，同位语从句中的谓语动词通常用“should+动词原形”的虚拟语气结构，其中should可以省略。
- The suggestion came from the chairman that the new rule (should ) be adopted.
直接引语与间接引语
各种句式的转换
陈述句
跟汉语类似主要that引导，that还可以省略，省事的感觉。
The doctor said to me,“You should take plenty of water and eat more vegetables.”
===>The doctor told me that I should take plenty of water and eat more vegetables.
疑问句
间接引语转化为陈述语序
He said,“Have you read this book?”
===>He asked me if/whether I had read that book.
祈使句
基本句式：主语+asked/told/ordered/begged/advised+sb. to do…
The hostess said to us,“Please sit down.”
===>The hostess asked us to sit down.
感叹句
“what a smart girl she is!” they praised.
==>They praised what a smart girl she was.
直接引语变间接引语的时候在人称、时态、动词等方面需要根据具体的情景进行变化
人称变化
直接引语第一人称，间接引语第三人称，跟汉语一样，不用多注意。
时态变化
转述式向前推一个时态
比如：
直接引语一般现在—》间接引语一般过去
直接引语一般过去—》间接引语过去完成
直接引语一般将来—》间接引语过去将来
直接引语现在完成—》间接引语过去完成
指示代词、时间状语、地点状语、方向性动词及情态动词的变化
时态不需要变化
直接引语有确定的过去时间
He said,“The story took place in the 1930s.”
===>He said that the story took place in the 1930s.
只着眼于转述事实，而不侧重动作先于转述动作的时间
The boy said,“I found the dog just at the edge of the wood.”
===>The boy said that he found the dog just at the edge of the wood.
所转述的动作或状态说话时仍在继续，并对此点加以强调
The reporter said,“The war in the Middle East is now still on.”
===>The reporter said that the war in the Middle East is now still on.
所转述的是自然现象、科学真理、名言警句等，并对此加以强调
Our English teacher said,“All work and no play makes Jack a dull boy.”
===>Our English teacher told us that all work and no play makes Jack a dull boy.
在when，while，since等引导的时间状语从句中
He said,“It is many years since he came to live here.”
===> He said that it was many years since he came to live there.
直接引语中含有某些没有过去式的情态动词时，变为间接引语时可用原来形式，也可用其他适当表示法。但要注意保持原来意义
He said,“You must be very fond of art.”
===>He said that I must be very fond of art.
直接引语时习惯性行为
He said,“I usually get up at 5:30 and go to school at 7:00.”
===>He said that he usually gets up at 5:30 amd goes to school at 7:00.
直接引语中的状语…days ago是从说话人说话算起
He said,“I met her three days ago.”
===>He said that he met her three days before.
直接引语中的动作或状态或发生的时间未到
"I’ll be coming tomorrow,"she said.
===>She said that she’ll be coming the next day.
直接引语中的谓语动词时虚拟语气
I insisted,“You should give up smoking and drinking.”
===>I insisted that he should give up smoking and drinking.
