名詞性從句相當于名詞，可分別作主句的主語、表語、賓語和同位語。因此，名詞性從句廳分為主語從句、表語從句、賓語從句和同位從句。
（一）引導名詞性從句的連接詞
1、連接代詞：who, whose, whom, what, which。有詞義，在從句中擔任成分，如主語、表語、賓語、或定語等。
2、連接副詞：when, where, why, how。有詞義，在從句中擔任成分，作狀語。
3、連接詞：that, whether, if, as if。that 無詞義，在從句中不擔任成分，有時可省略；if (whether), as if雖有詞義，但在從句中不擔任成分。
注意：連接代詞與連接副詞在句中不再是疑問句，因而從句中謂語不用疑問式。連接代詞與連接副詞在從句充當句子成分，連接詞whether 和if（是否），as if（好象）在從句中不充當句子成分，只起連接作用。根據句義，如果連接代詞與連接副詞，whether、if 和as if都用不上時，才用that作連接詞（that本身無任何含義）。
（二）主語從句
1、主語從句在復合句作主語。
e.g. Who will go is not important.
2、用it作形式主語，主語從句放在句末。
e.g. It doesn’t matter so much whether you will come or not.
3、that引導主語從句時，不能省略。
e.g. That he suddenly fell ill last week made us surprised.
（三）表語從句
1、表語從句在復合句中作表語，位于系動詞之后。
e.g. The question was who could go there.
2、引導表語從句的連接詞that有時可省去。
e.g. My idea is (that) we can get more comrades to help in the work.
（四）賓語從句
1、賓語從句在復合句中作賓語。引導賓語從句的連詞that一般可省略。
e.g. I hope (that) everything is all right.
2、介詞之后的賓語從句，不可用which或if連接，要分別用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與if都可以引導賓語從句，常可互換。但下面情況不能互換。
①賓語從句是否定句時，只用if，不用whether。
e.g. I wonder if it doesn’t rain.
②用if 會引起誤解，就要用whether。
e.g. Please let me know whether you want to go.（此句如果把whether改成if，容易當成條件句理解）
③賓語從句中的whether 與or not直接連用，就不能換成if；不直接連用，可換。
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介詞后的賓語從句要用whether引導。whether 可與不定式連用。whether也可引導主語從句、表語從句、同位語從句，還可引導讓步狀語從句，以上均不能換成if。但引導條件從句時，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）同位語從句
同位語從句在句中作某一名詞的同位語，一般位于該名詞（如：news, fact, idea, suggestion, promise等）之后，說明該名詞的具體內容。
e.g. I have no idea when he will be back.
The fact that he had not said anything surprised everybody.
語法經典練習：
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