同位语:
一个名词（或其它形式）对另一个名词或代词进行修饰，限定或说明，这个名词（或其它形式）就是同位语。
同位语与被它限定的词的格式要一致，并常常紧挨在一起。同位语从句即重复说明同一个称谓或事件的从句。
1.名词作同位语
Mr Wang,my child’s teacher,will be visiting us on Tuesday.
王先生，我孩子的老师，星期二要来看我们。
（在这里'my child's teacher'做同位语修饰'Mr Wang')
2.短语作同位语
I,the oldest girl in the family,always had to care for the other children.
我，作为家里最大的女孩，总是要照料家中的其他孩子。
直接引语作同位语
But now the question comes to their minds，“Did she die young because she was a clone?”
但是现在他们不得不思考这样的问题：“多莉早死是因为它是一只克隆羊吗？”
3.句子作同位语
The girls were surprised at the fact that ocean ships can sail up the Great lakes.
巨大的海轮可以开到五大湖，让表姐妹俩感到吃惊。

同位语从句的引导词：
引导同位语从句的词语通常有连词that，whether，连接代词和连接副词等。
1. 由that引导
We heard the news that our team had won.
我们听到消息说我们队赢了。
They were worried over the fact that you were sick.
他们为你生病发愁。
The news that we are having a holiday tomorrow is not true.
明天放假的消息不实。
I’ve come to the conclusion that it was unwise to do that.
我得出结论这样做是不明智的。
The fact that the money has gone does not mean it was stolen.
那笔钱不见了这一事实并不意味着是被偷了。
He referred to Copernicus’ statement that the earth moves round the sun.
他提到了哥白尼关于地球绕太阳转的说法。
【注意1】在某些名词(如demand, wish, suggestion, resolution等)后面的同位语从句要用虚拟语气。如：
They were faced with the demand that this tax be abolished.
他们面对废除这个税的要求。
They expressed the wish that she accept the award.
他们表示希望她接受这笔奖金。
There was a suggestion that Brown should be dropped from the team.
有一项建议是布朗应该离队。
The suggestion that the new rule be adopted came from the chairman.
采纳新规则的建议是主席提出的。
The resolution that women be allowed to join the society was carried.
允许妇女参加这个协会的决议通过了。
I can understand their eagerness that you should be the main speaker.
我理解他们希望你作主要发言人的殷切心情。
【注意2】引导同位语从句的连词that通常不省略，但在非正式文体中也可以省去。如：
He gabbed his suitcase and gave the impression he was boarding the Tokyo plane.
他拿起了手提箱，给人的印象是他要登上飞往东京的飞机了。

2. 由whether引导
There is some doubt whether he will come. 他是否会来还不一定。
Answer my question whether you are coming. 你回答我的问题：你来不来。
The question whether it is right or wrong depends on the result. 这个是对还是错要看结果。
We are not investigating the question whether he is trustworthy. 我们不是在调查他是否可以信任的问题。
【注意】whether 可引导同位语从句，但if不能引导同位语从句。

3. 由连接代词引导
Have you any idea what time it starts?
你知道什么时候开始吗?
From 1985-90 I was an instructor at the regional party headquarters. After that I went back to work in a factory. Then I had no idea what a casino was.
从1985年到1990年我是地方党部的教员。随后我回到一家工厂工作。当时我不知道赌场是什么样的地方。

4. 由连接副词引导
I have no idea when he will come back. 我不知道他什么时候回来。
It is a question how he did it. 那是一个他如何做的问题。
He had no idea why she left. 他不知道她为什么离开。
You have no idea how worried I was! 你不知道我多着急!

同位语从句的用法:
同位语部分是个句子，就是同位语从句，这种用法比较"固定"
一、在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后面，用以说明该名词表示的具体内容。
I heard the news that our team had won．我听到了我们队获胜的消息。

二、可以跟同位语从句的名词通常有:
news，idea，fact，promise，question，doubt，thought，hope，message，suggestion，
words（消息），possibility等（一般的“抽象”名词都可用）。
I’ve come from Mr wang with a message that he won’t be able to see you this afternoon．
我从王先生那里来，他让我告诉你他今天下午不能来看你了。

三、英语中引导同位语从句的词通常有
连词：that，whether，
连接代词：what，who，
连接副词：how,when,where等。（注：if,which 不能引导同位语从句。）
He must answer the question whether he agrees to it or not.
他必须回答他是否同意这样一个问题。

四、有时同位语从句可以不紧跟在说明的名词后面，而被别的词隔开。
The thought came to him that maybe the enemy had fled the city．
他突然想起可能敌人已经逃出城了。

关于分离同位语从句
有时同位语从句可以和同位的名词分开。如：
The story goes that he beats his wife. 传说他打老婆。
The news got about that he had won a car in the lottery. 消息传开说他中彩得了一辆汽车。
The rumour spread that a new school would be built here. 谣传这里要盖一所新学校。
Report has it that the Smiths are leaving town. 有传言说史密斯一家要离开这座城市。
The thought came to him that maybe the enemy had fled the city. 他想到可能敌人已逃离这座城市。
The order soon came that all citizens should evacuate the village. 不久命令下来，所有居民都必须撤出村子。

间隔同位语从句
同位语从句通常是跟在它解释或说明的名词后，但有些情况下，由于句子结构的原因，同位语从句不紧跟在名词后，而被其他的词隔开。
A warm thought suddenly came to me that I might use the pocket money to buy some flowers for my mother's birthday
简析：由于that从句太长，为避免句子失去平衡，此处用了间隔同位语从句

suggestion,request和order等名词后的同位语从句用虚拟语气。
She made a request that the doctor(should)be sent for at once.她请求立即请医生来。
简析：suggestion，order，request，proposal，requirement，command，advice，proposition和recommendation等名词后接同位语从句时，从句中的谓语动词要用“（should+）动词原形”的形式，其中should一词可省略。