名词从句是由陈述句和问句变化而来的，和动名词，不定式短语一样，也要视作名词，具有名词的性质。
一.名词从句分类

二.名词从句的作用

I 做主语
Eg.

  1. That honesty is the best policy is a proverb （which） we should always keep in mind.
  2. Where he lives is still a doubt .
  3. Whether he can do it remains to be seen.

名词从句做主语有时会造成主语过长，通常可用代词it代替置于句。而被代替的名词从句置于句尾。因此上面的三个句子可以分别改为：

  1. It is a proverb we should always keep in mind that honesty is the best policy.
  2. It is still a doubt where he lives.
  3. It remains to be seen whether he can do it.

II.做动词宾语
Eg.

  1. I know that he will go abroad in the nearest future.
  2. I wonder whether he has finished the work.
  3. I don’t know how he’ll handle it.

III.做介词宾语
用whether和疑问词引导的名词从句可做宾语，但是that引导的名词从句不能做介词的宾语。
Eg.

  1. I am worried about whether he can do it.
  2. I am suspicious of how he’ll cope with the problem.

如果遇到介词，且一定要用that从句的情况，有两种补救办法。
a.介词+the fact+that从句
Eg.

  1. I am sure of the fact that the team has won the game.

b.保留介词，但不加that，且介词后的that从句做适当变换。
第一步： 除去that
第二步：that之后的主语变成所有格
第三步：动词变成动名词
Eg.

  1. I am worried about that he plays around all day.(×)
    这个句子是错误的，应改为：
    I am worried about his playing around all day.（√）

如果that从句里面有助动词do,does,did时，去掉即可。
Eg.

  1. I am worried about that he doesn’t study.(×)
    这个句子错误，应改为：
    I am worried about his not studying.（√）

如果that从句里面有助动词will或would，去掉即可，或改为be going to.再将be动词转变成动名词being。
Eg.

  1. I am sure of that the team will win the game.(×)
    这个句子错误，有两种该法：
    a.I am sure of the team’s winning the game.（√）
    b.I am sure of the team’s being going to win the game.（√）