在备考的过程中，从句的学习一直以来都不是一件容易的事情，更不用说要面对那些长得很像的从句：如同位语从句&定语从句，它们可谓是从句界的“双胞胎”，那今天我们就从其相同点和不同点来深入了解一下它们吧！
相同点
主句都完整
同位语从句
虽然同位语从句属于名词性从句(主语从句/宾语从句/表语从句/同位语从句)，但实际上名词性从句中，只有同位语从句的主句是完整的。
如：We all know the fact [that you are a kind person].
【分析】
主句是 We all know the fact---主谓宾结构完整。[主语We/谓语 know/宾语the fact]
定语从句
This is a book[that her father bought her].
【分析】
主句是This is a book ---主系表结构完整。[主语this/系动词is/表语a book]
都可以用that 引导
同位语从句
We all know the fact [that you are a kind person].
【分析】
从句是由连接词that引导：that you are a kind person
定语从句
This is a book[that her father bought her].
【分析】
从句是由连接词that(定从中也叫关系代词)引导: that her father bought her
不同点
……
从句前的名词类型不完全相同
同位语从句前的名词常用抽象名词(promise/fact/news/belief/suggestion...)；定语从句前的先行词可以是抽象名词，也可以是具体名词。
We all know the fact[that you are a kind person].
【分析】fact 表事实，是抽象名词。
This is a book[that her father bought her].
【分析】book 表书，是具体名词
She told me the fact[that she had told others several days ago].
【分析】fact表事实，是抽象名词。
从句与前面名词的关系不同
同位语从句等同于前面的抽象名词；
定语从句不等同于前面的名词。
We all know the fact [that you are a kind person].
【分析】 从句=抽象名词
“你是一个善良的人”等同于“事实”
This is a book[that her father bought her].
【分析】 从句≠具体名词
“她爸爸给她买的” 不等同于“书”
She told me the fact[that she had told others several days ago].
【分析】从句≠具体名词
“她几天之前告诉过其它人的”不等同于“事实”
连接词在从句中作不作成分不同
同位语从句中的that 不作从句的主要成分(主要成分是指主语/宾语/表语等)
定语从句中的that作从句的主要成分
We all know the fact[that you are a kind person].
【分析】从句中的you are a kind person 是主系表结构，不缺少主要成分，所以that不作从句任何成分，没有含义，只起到连接作用，但不能省略。
This is a book[that her father bought her].
【分析】 从句中的her father bought her，看起来好像是主谓宾结构，但实际上结构不完整，因为讲话者想表达 her father bought her (that=a book)是主谓双宾结构. 所以，that充当从句的bought 的宾语。
【注意】buy sb sth
She told me the fact[that she had told others several days ago].
【分析】从句中的she had told others several days ago，看起来好像是主谓宾结构，但实际上结构不完整，因为讲话者想表达 she had told other (that=the fact)是主谓双宾结构. 所以，that充当从句的told的宾语。
【注意】tell sb sth
最后让我们回顾一下~
