定语从句和同位语从句的区别

1、和先行词的关系不同。同位语从句说明先行词的具体内容，二者是同位关系;定语从句修饰限定先行词，二者是修饰关系。

The news that he told me is that Tom would go abroad next year.

他告诉我的消息是汤姆明年将出国.

(第一个that引导的从句是定语从句,that在从句中作宾语)

The news that Tom would go abroad is told by him.

汤姆要出国的消息是他讲的.

(同位语从句,that在句中不作任何成分)

2、定语从句由关系代词或关系副词引导，关系词在从句中担当相应的句子成分，作宾语时经常被省略。同位语从句主要有连词that引导，在从句中不担当成分，也可由when、where、who、how、what、whether等连词引导，这些连词在从句中担当成分。

The news that he told me is true.(定语从句)

他告诉我的消息是真的。

The news that he will come back is true.(同位语从句)

他将要回来的那个消息是真的。

3、同位语从句和先行词可以用be动词发展成为一个完整的句子，而定语从句不能。

The fact that the earth moves around the sun is known to all. (同位语从句)

地球围绕太阳转，这个事实人人皆知。

The fact is that the earth moves around the sun. (定语从句)