名词性从句相当于名词，可分别作主句的主语、表语、宾语和同位语。因此，名词性从句厅分为主语从句、表语从句、宾语从句和同位从句。
（一）引导名词性从句的连接词
1、连接代词：who, whose, whom, what, which。有词义，在从句中担任成分，如主语、表语、宾语、或定语等。
2、连接副词：when, where, why, how。有词义，在从句中担任成分，作状语。
3、连接词：that, whether, if, as if。that 无词义，在从句中不担任成分，有时可省略；if (whether), as if虽有词义，但在从句中不担任成分。
注意：连接代词与连接副词在句中不再是疑问句，因而从句中谓语不用疑问式。连接代词与连接副词在从句充当句子成分，连接词whether 和if（是否），as if（好象）在从句中不充当句子成分，只起连接作用。根据句义，如果连接代词与连接副词，whether、if 和as if都用不上时，才用that作连接词（that本身无任何含义）。
（二）主语从句
1、主语从句在复合句作主语。
e.g. Who will go is not important.
2、用it作形式主语，主语从句放在句末。
e.g. It doesn’t matter so much whether you will come or not.
3、that引导主语从句时，不能省略。
e.g. That he suddenly fell ill last week made us surprised.
（三）表语从句
1、表语从句在复合句中作表语，位于系动词之后。
e.g. The question was who could go there.
2、引导表语从句的连接词that有时可省去。
e.g. My idea is (that) we can get more comrades to help in the work.
（四）宾语从句
1、宾语从句在复合句中作宾语。引导宾语从句的连词that一般可省略。
e.g. I hope (that) everything is all right.
2、介词之后的宾语从句，不可用which或if连接，要分别用what或 whether。
e.g. I’m interested in whether you’ve finished the work..
I’m interested in what you’ve said.
3、whether与if都可以引导宾语从句，常可互换。但下面情况不能互换。
①宾语从句是否定句时，只用if，不用whether。
e.g. I wonder if it doesn’t rain.
②用if 会引起误解，就要用whether。
e.g. Please let me know whether you want to go.（此句如果把whether改成if，容易当成条件句理解）
③宾语从句中的whether 与or not直接连用，就不能换成if；不直接连用，可换。
e.g. I don’t know whether or not the report is true.
I don’t know whether/ if the report is true or not.
④介词后的宾语从句要用whether引导。whether 可与不定式连用。whether也可引导主语从句、表语从句、同位语从句，还可引导让步状语从句，以上均不能换成if。但引导条件从句时，只能用if，而不能用whether。
e.g. It depends on whether we have enough time.
They don’t know whether to go there.
Please come to see me if you have time.
（五）同位语从句
同位语从句在句中作某一名词的同位语，一般位于该名词（如：news, fact, idea, suggestion, promise等）之后，说明该名词的具体内容。
e.g. I have no idea when he will be back.
The fact that he had not said anything surprised everybody.
语法经典练习：
1.The fact ____ she works hard is well known to us all.
A. that B. what C. why D. which
2.The fact ____ he was successful proves his ability.
A. that B. what C. which D. why
3.The news ____ he was kidnapped surprised us greatly.
A. what B. that C. why D. when
4.His suggestion ____ the meeting be delayed was turned down.
A. which B. that C./ D. it
5.I have no idea ____ he will start.
A. when B. that C. what D./
6.I've come from the government with a message ____ the meeting won't be held tomorrow.
A. if B. that C. whether D. which
7.The thought ____ he might fail in the exam worried him.
A. when B. which C. what D. that
8.The order ____ the prisoner be set free arrived too late.
A. which B. whether C. that D. what
9.The nurses are trying their best to reduce the patient's fear ____ he would die of the disease.
A. that B. as C. of which D. which
10.He often asked me the question ____ the work was worth doing.
A. whether B. where C. that D. when
11. Along with the letter was his promise ____ he would visit me this coming Christmas.
A. which B. that C. what D. whether
12. The other day, my brother drove his car down the street at ____ I thought was a dangerous speed.
A. as B. which C. what D. that
13. Luckily, we’d brought a road map without ____ we would have lost our way.
A. it B. that C. this D. which
14.There are signs ____ restaurants are becoming more popular with families.
A. that B. which C. in which D. whose
15. We can see the same signs ____ stand out throughout the city.
A. that B. which C. in which D. whose
Keys: 1-5 AABBA 6-10 BDCAA 11-15 BBDAA