在复合句主句中名词性成分之后与该名词性成分并列，补充说明该名词性成分的有关情况的名词性从句， 被称为同位语从句。
同位语从句例句-that引导
例句：He referred to Copernicus’ statement that the earth moves round the sun.
解析：在某些名词(如suggestion, resolution等)后面的同位语从句要用虚拟语气。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。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。
同位语从句例句-由whether引导
例句：We are not investigating the question whether he is trustworthy
解析：whether 可引导同位语从句，但if不能引导同位语从句。
同位语从句例句-连接代词引导
例句：Have you any idea what time it starts?
解读：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。
同位语从句例句-连接副词引导
例句：I have no idea when he will come back.
同位语从句的先行词
通常为answer, hope, fact, truth, belief, news, idea, promise, information, conclusion, order, suggestion, problem, question, thought, report, belief, decision, doubt, opinion, theory等抽象名词。
同位语从句的引导词
通常有连词that，whether，连接代词和连接副词等。
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)
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”)
