名詞性從句包括：主語從句、表語從句、賓語從句和同位語從句。引導名詞性從句的連詞有：
a.連詞：that, whether, if（這三個詞都不作從句的成分，同時，that無含義，而whether和if都表“是否”）
b.疑問代詞：who, whom, whose, what, which
c.疑問副詞：when, where, why, how
（一）主語從句
? 在復合句中充當主語的從句。
引導主語從句
? ?that引導主語從句時不同于其他的連詞，既無詞義也不作成分，只起單純的連接作用，且通常不可以省。為了強調(diào)that引導的主語從句而置之于句首時，that不可省。
? ?①That the driver could not control his car was obvious.
? ?②That she was chosen made us very happy.
? ?③That he will come is certain.
? ?④That he would take the risk is true.
? ?⑤That he should have married her isn't surprising.
★通常，that引導主語從句時用it做形式主語，把從句置于句尾，此時that有時可省。例如：
? ?①It was obvious that the driver could not control his car.
? ?②It made us very happy that she was chosen.
? ?③It is certain that he will come.
? ?④It is true that he would take the risk.
? ?⑤It isn't surprising (that) he should have married her.
★如果以that從句為主語的句子是疑問句，就只能用先行詞it結(jié)構(gòu)。例如：
? ?①Is it certain that he will come?
? ?②Is it true that he would take the risk?
▲it做形式主語有以下幾種不同的結(jié)構(gòu)：
(1)it + be + 形容詞+ that-從句
?①It is likely that he will come.
?②It is strange that she has ever trusted him.
?③It is important that he（should) attend the meeting.
?④It is best that he (should) go.
? ?此句型在表示驚訝、喜悅、遺憾等感情色彩時，that從句中的謂語動詞也常用（should）+ v原形。
? ? It is strange that no one should have objected to the plan.
(2)it + be +名詞+ that-從句
? ? ?It is common knowledge that the whale is not a fish...
? ? ?It's a pity that he should have massed the train.
(3) it + be + -ed分詞 + that從句
? ? ?It is said that he is a famous writer.
? ? ?It is reported that there will be a storm this afternoon.
▲在表示建議、要求、命令等意義的被動結(jié)構(gòu)中，that從句中的謂語動詞常用（should）do。（參見虛擬語氣部分）
? ? It is suggested that the meeting(should）be held this afternoon.
? ? It?is demanded that he (should) leave at once.
(4) it + seem/happen/appear等不及物動詞+that從句。（look不接that從句，它接to be結(jié)構(gòu)或形容詞）
? ? ?It seems that he is wrong.
? ? ?It appears that they are in urgent need of help.
? ? ?He looks (to be) surprised/happy/sad.
2. whether引導主語從句，意為“是否”，只起連接作用，不充當任何成分。(置于句首時必須用whether引導，置于句尾時，間或可用if。)
? ? Whether he will win the game is not clear.
? ? Whether he will come is uncertain.
? ? Whether she comes or not doesn't concern me.
? ? It is not clear whether/if he will come.
? ? It was uncertain whether he would come.