如果我们把句子当作名词来使用，分别在另一个句子中作主语、宾语、表语和同位语，于是就构成了四种从句：主语从句、宾语从句、表语从句和同位语从句。因为以为这四种从句在本质上相当于名词的作用，所以我们把他们统称为名词从句。
上面说到名词从句就是用一个完整句子充当另一个句子的某种句子成分便构成了具体某一名词从句。
陈述句可分别充当四种句子成分，要在陈述句首加上that。
对于陈述句，我们要在句首加上that，然后把“that+陈述句”分别放在另一个句子的四种位置即构成四种名词从句。
1.主语从句。“that+陈述句”在主语位置即成主语从句：
Stuart is ugly.
That Stuart is ugly is a fact..
That Malaysians don’t speak good English is obvious.
更常见的是用it式主语置于句首，而将主语从句放在句末。例如：
It is a fact that Stuart is ugly.
It is obvious that Malaysians don’t speak good English。
因此下面都是常见的主语从句句型：
①It is +过去分词 +that 从句
②It is +形容词 +that 从句
③It is +名词 +that 从句
2. 宾语从句。“that+陈述句”在宾语位置即成宾语从句：
I thinkyou turned off the light.
We knowwomen love shopping.
She believedher child was premature.
只有宾语从句中的that才可以省去，其他名从that不省。
3.表语从句。“that+陈述句”在表语位置即成表语从句：
My idea is that the students should be more open to each other.
The reason is that he was careless and irresponsible.
4.同位语从句。“that+陈述句”在同位语位置即成同位语从句：
所谓同位语，就是用来补充说明名词的成分。
The rumor that Tom washed his socks once a month turned out to be untrue.
Our fathers brought forth upon this continent a new nation， conceived in liberty and dedicated to the proposition that all men are created equal.
A saying goes that tomorrow is another day.
