同位语从句属于名词性从句，大多由从属连词that引导，常常跟在fact，idea，opinion，news，hope，belief等名词后面。同位语从句一般用来解释或说明这些名词的具体含义或内容，在逻辑上表现为同位关系。例如：
They are familiar with the opinion that all matter consists of atoms.他们很熟悉这一观点，所有的物质都是由原子构成的。
1、从先行词来看
同位语从句与名词之间在逻辑上是"主语+be+表语"的关系。该名词是需要做特殊说明的抽象名词。例如：
They were delighted at the news that their team had won.当听到他们的球队赢了的消息时，他们欣喜若狂。
2、从引导词来看
引导词that在同位语从句中是连词，只起连接作用，无具体词义，that不可省略;that在定语从句中是关系代词，它在从句中充当一定成分——主语或宾语，有具体词意，作宾语时还可以省略。试比较：
The factory(that)we visited yesterday is a chemical one.我们昨天参观的那家工厂是化工厂。(that在从句中作宾语，所以此句是宾语从句)
The news that he will leave for Shanghai is true.他将要去上海的消息是真的。(that只起连接从句的作用，所以此句是同谓语从句)
They are familiar with the opinion that all matter consists of atoms.他们很熟悉这一观点，所有的物质都是由原子构成的。
1、从先行词来看
同位语从句与名词之间在逻辑上是"主语+be+表语"的关系。该名词是需要做特殊说明的抽象名词。例如：
They were delighted at the news that their team had won.当听到他们的球队赢了的消息时，他们欣喜若狂。
2、从引导词来看
引导词that在同位语从句中是连词，只起连接作用，无具体词义，that不可省略;that在定语从句中是关系代词，它在从句中充当一定成分——主语或宾语，有具体词意，作宾语时还可以省略。试比较：
The factory(that)we visited yesterday is a chemical one.我们昨天参观的那家工厂是化工厂。(that在从句中作宾语，所以此句是宾语从句)
The news that he will leave for Shanghai is true.他将要去上海的消息是真的。(that只起连接从句的作用，所以此句是同谓语从句)
