1.名词的成分：主语，表语，宾语和同位语，那么对应的，从句为:主语从句，表语从句，宾语从句和同位语从句。

名词性从句用的词叫引导词，
常用的引导词有：
that
whether/if 其中whether可以引导所有名词性从句，if只能引导宾语，即if引导名词性从句不能放在句首
特殊疑问词：包括链接副词 when where why how；连接代词：who whom what which whose
此外注意：所有从句都是陈述句语气

主语从句：一般That 引导，例如 That she is so beautiful makes me happy！ 由于that 放在句首头重脚轻，所以一般用it改写

变成it makes me happy that she is so beautiful。 这里it只是形式主语。真正主语是后面that引导的从句。这里that作主语不能省略。
但是如果变成it is 。。。that。。。这里that可以省略。
名词性从句省略引导词
作主语不能省略（位于句首而且作主语时候）
作宾语和补语可以

同位语从句：解释说明的句子，一般that 引导Nothing can hide the truth that she is growing old

这里的that 不做任何成分，只是引导同位语从句，后面是一个完整句子，区别定语从句

But the idea that journalist must understand the law more profoundly than an ordinary citizen rests on an understanding of the established conventions and special responsibilities of the news media.

Evidence came up that specific speech sounds are recognized by babies as young as 6months old.
这里came up 是不及物不需要跟宾语，所以这里的that引导的还是同位语从句

宾语从句

一般实义动词后面有引导就是宾语从句
She said that she would go to the US soon.
I wonder if/whether I will pass the exam smoothly.
这里有个考点if和whether区别
if引导名词性从句不能位语句首，而whether可以。
Whether Shrek married Princess Fiona is improtant！

I do not know whether/if he will come or not.

间接疑问句：

1.不含有特殊疑问词
Can you tell me whether you love me or not？
2.含有特殊疑问词（陈述句语气）
Can you tell me who you are ？
Do you know what it is 、

简介疑问句可以作宾语、表语
I do not know what she just said
The most important thing is that who she is

总结一下:

1.名词作主宾补
2.在完整句子前面加上that就可以变成有主语和谓语的名词性从句
3.that 引导名词性从句作主宾补，主语而且位于句首的时候that不能省略
4.that引导的名词性从句是包含主语和位语的完整句子
5.名词性从句无论是否有疑问都是陈述句语气

参考《不就是语法和长难句吗》和《英语分解语法大全》