名词性从句包括：主语从句、宾语从句、表语从句、同位语从句，多由连词that，wh-疑问词或由what，whatever等关系代词引导。本文总结如下：
1.主语从句
1)主语从句在句子中充当主语，句子的谓语动词用第三人称单数。如：
Why he refused to work with you is still mystery.他为什么拒绝和你一起工作，仍不得其解。
Whoever comes is welcome.不论谁来，都是受欢迎的。
2)主语从句前的that不能省略，有时为了保持句子平衡，that从句后置，而由it作形式主语。如：
That he became a lawyer may have been due to his mother's influence.他能成为律师可能归因于他母亲的影响。
It is not true that he has moved to New York.事实上他没去纽约。
2.宾语从句在句子中充当宾语。如：
I don't know where the sound came from.我不知道声音是从哪里来的。
Don't be satisfied with what you have achieved.不要满足于你已取得的成绩。
3.当从句放在系动词be，look，remain，seem等后即构成表语从句。
The trouble is that I have lost his address.麻烦的是我弄丢了他的地址。
4.同位语从句
1)同位语从句是对与之同位的名词中心词作进一步解释。能接名词性从句的常见名词有：idea, fact, news, belief, hope, evidence, opinion, problem, truth, answer, proposal, theory, decision, discovery, thought, understanding等。
The news that he has passed the examination is exciting.他通过考试的消息令人振奋。
2)同位语从句与定语从句的区别在于：定语从句是对先行词加以修饰、限制，而同位语从句说明中心词的具体内容；that在定语从句中充当成分，为关系代词，而在同位语从句中不作任何成分，仅起连词作用。如：
The fact that we talked about is very important.(定语从句)我们讨论的情况非常重要。
The fact that he succeeded in the experiment pleased everybody.(同位语从句)他实验成功的事实使每个人都很高兴。
5. whether与if在名词性从句中的区别
if一般只用于引导宾语从句，而whether除引导宾语从句外，还可以引导其他名词从句。
1)连词whether引导的主语从句、表语从句不能用if来替换。
Whether he will attend the meeting is uncertain.他是否来参加会议还不确定。
The question is whether he will come.问题是他是否来。
2)宾语从句中，whether常与or not搭配，可以说whether or not，而不说if or not。
I don't care whether or not she will attend the meeting.她是否来参加会议，我不介意。
3) whether可用在介词后，或带to的不定式前，if则不可。
She doesn't know whether to get married now or wait.她不知道是现在结婚呢还是等等。
I haven't settled the question of whether I'll go back home.我还没决定下来是否回家。
4)某些动词后面(如discuss)只能用whether,不用if。
We discussed whether we should go on climbing.我们讨论了是否继续攀登。
