同位语从句指的是在复合句中充当同位语的从句，属于名词性从句的范畴，同位语从句用来对其前面的抽象名词进行解释说明，被解释说明的词和同位语在逻辑上是主表关系。
1. that引导同位语从句。
在下列名词后可用that引导同位语从句answer, belief, doubt, fact, hope, idea, information, knowledge, law, news, opinion, plan, suggestion, thought, truth等。
I had no idea that you were here.
The story goes that William killed his wife.
He always works hard in spite of the fact that he is not in good health.
Suddenly the thought came to me that he would go blind.
注意：
①同位语从句引导词that无含义，不充当成分，不可省略。
②同位语从句与其说明的名词或代词为同一内容，故可以用is把前边的中心词和从句连接成一个句子。
③同位语从句前一般没有逗号。
that引导同位语从句与引导定语从句的区别：that引导同位语从句时只起连接作用，不充当任何成分;that引导定语从句时，在从句中要作成分，如主语、宾语等。
①He told me the news that our team won.(that引导同位语从句)
②The news that / which he told me was very exciting.(that引导定语从句，在从句中作宾语)
2. 在no idea, question, problem等后可用wh-疑问词引导同位语从句，if不引导同位语从句。
I have no idea where he has gone.
I have no idea what he said.
3. 辨析：引导名词性从句时what与whatever, who与whoever的区别：
what 与whatever：
What you want has been sent here.(what = the thing(s) that/all that/anything that特指)
Whatever you want makes no difference to me.(whatever = anything that泛指)
What caused the accident was a broken bottle.(特指)
Whatever caused the accident has not yet been found.(泛指)
who 与whoever：
Who will go to Beijing on business has not been decided.(who表疑问，表示“谁”，“哪一个”)
Whoever breaks the law should be punished.(whoever = anyone who，表示“无论哪个人”)
4. 同位语从句注意与定语从句区别，同位语从句对前一名词做补充说明，在从句中无语法位置，而定语从句所修饰词在从句中占一语法位置如：
The idea that one can do the work without thinking is wrong.(同位idea在从句中无位置，而从句只是具体说明idea的内容)
The idea that you put forward at the meeting is wrong.(定语从句，idea做put forward 的宾语)
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