根据名词性从句的句法功能，可分为主语从句、宾语从句、补语（表语）从句及同位语从句。

1.

The fact was (that) John Brown had a car accident. [subject complement]

The nominal clause here is used as subject complement. This construction is used when one wishes to state a fact, a truth, etc, or one’s opinion belief, etc. Some of the commonly used subjects of this construction are: the fact, the truth, the problem, my opinion/view, his belief/explanation. etc.

可以接主语从句的系动词有be, look, seem, remain等，引导主语从句的that常可省略。

2.

The scissors are not what I need. [subject complement]

The nominal clause is used as subject complement introducing by a wh-word.名词性从句中，关系代词what在句中起连接作用，同时又充当从句中的一个成分，而that在句中只起连接作用，不充当从句中的成分。Reading is to mind what food is to the body.

读书之于精神犹如粮食之于身体。

A is to B what C is to D.

3.

Have you heard the news that all English students will have to pass a proficiency test before they can graduate? [apposition]

The nominal clause is used as the appositive对名词作进一步的解释，说明名词的具体内容. The nouns that can be in apposition to nominal clause include belief, fact, hope, idea, doubt, news, rumor, conclusion, suggestion, problem, information, report, law等

定语从句（形容词性分句）与同位语从句的区别：一，定语从句中的that既代替先行词，同时又在从句中作某个成分，that充当宾语时常可被省略；而同位语从句中的that是连词，只起连接主句和从句的作用，不充当任何成分，that一般不可以省略。二，定语从句是形容词性的，功能是修饰先行词，对先行词加以限定，描述它的性质或特征；同位语从句等同于先行词，是名词性的，其功能是对名词作补充说明。三，同位语从句中的名词是表示抽象概念的名词，而定语从句的先行词可以是表示抽象概念或具体概念的词：

The rumor that he stole the ring proved groundless. [apposition]

The rumor (that) he spread among the students has been denied. [relative clause]

他（在同学们中间散布的）流言被否认了。

4.

What I told him [subject clause] was (that) I would find him a good play. [subject complement]

The nominal clause introduced by what here is used as subject of the sentence. Subject clauses may also be introduced by other wh-words.

e.g. How he did it remains a mystery..

Why he came so late has never been explained.