名词性从句包括：主语从句、表语从句、宾语从句和同位语从句。引导名词性从句的连词有：a.连词：that, whether, if（这三个词都不作从句的成分，同时，that无含义，而whether和if都表“是否”）b.疑问代词：who, whom, whose, what, whichc.疑问副词：when, where, why, how（一）主语从句 在复合句中充当主语的从句。1.that引导主语从句 that引导主语从句时不同于其他的连词，既无词义也不作成分，只起单纯的连接作用，且通常不可以省。为了强调that引导的主语从句而置之于句首时，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引导主语从句时用it做形式主语，把从句置于句尾，此时that有时可省。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从句为主语的句子是疑问句，就只能用先行词it结构。例如： ①Is it certain that he will come? ②Is it true that he would take the risk?▲it做形式主语有以下几种不同的结构：(1)it be 形容词 that-从句 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. 此句型在表示惊讶、喜悦、遗憾等感情色彩时，that从句中的谓语动词也常用（should） v原形。 It is strange that no one should have objected to the plan.(2)it be 名词 that-从句 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分词 that从句 It is said that he is a famous writer. It is reported that there will be a storm this afternoon.▲在表示建议、要求、命令等意义的被动结构中，that从句中的谓语动词常用（should）do。（参见虚拟语气部分） 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等不及物动词 that从句。（look不接that从句，它接to be结构或形容词） 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引导主语从句，意为“是否”，只起连接作用，不充当任何成分。(置于句首时必须用whether引导，置于句尾时，间或可用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.
名词性从句之主语从句的用法