一、名詞性從句的基本概念
在復(fù)合句中起名詞作用的從句叫名詞性從句，包括作主語(yǔ)從句、表語(yǔ)從句、賓語(yǔ)從句和同位語(yǔ)從句。
(1)主語(yǔ)從句
就是在復(fù)合句中作主語(yǔ)的從句。主語(yǔ)從句常用that, whether, who, whom, whose, what, which, when, where, how, why, whatever, whoever等引導(dǎo)。如：
Whether he will be able to come remains a question. 他是否來(lái)還是問(wèn)題。
That China is a great socialist country is well known. 眾所周知，中國(guó)是一個(gè)偉大的社會(huì)主義國(guó)家。
注：為避免頭重腳輕，使句子平衡，常用it作形式主語(yǔ)，而將主語(yǔ)從句后置。如上述第二例常說(shuō)成：
It is well known that China is a great socialist country.
但是，由連接代詞what, whatever, whoever等引導(dǎo)的主語(yǔ)從句一般不能用形式主語(yǔ)。如：
What he found surprised me greatly. 他的發(fā)現(xiàn)使我非常吃驚。
Whoever is finished may rest. 凡是做完工的人都可以休息。
(2)表語(yǔ)從句
就是在連系動(dòng)詞之后作表語(yǔ)的從句。引導(dǎo)表語(yǔ)從句的連接除與引導(dǎo)主語(yǔ)從句的連接詞外，還有as if， as though。如：
The question is whether he is able to do it alone. 問(wèn)題是他能否單獨(dú)做這件事。
It looks as if (though) it is going to snow. 天好像要下雪似的。
注意：要區(qū)分以下句式：
1. that’s why+結(jié)果;that’s because+原因。2. the reason why /for…is that…
He is absent. That’s because he is ill. 他缺席，這是因?yàn)樗×恕?/p>
He is ill. That’s why he is absent. 他病了，這就是他缺席的原因。
The reason why he is absent is that he is ill. 他缺席的原因是他生病了。
(3)賓語(yǔ)從句
就是在復(fù)合句中作賓語(yǔ)的從句。引導(dǎo)這賓語(yǔ)從句的連接詞與引導(dǎo)主語(yǔ)從句的連接詞基本相同。如：
They didn’t say which they wanted. 他們沒(méi)有說(shuō)他們想要哪一個(gè)。
I am sure (that) no harm will ever come to you. 我肯定你永遠(yuǎn)不會(huì)受傷害。
I was surprised at what has happened.我對(duì)發(fā)生的事感到驚訝。
注意：當(dāng)think, believe, suppose等的疑問(wèn)式后面跟連接代詞或連接副詞引導(dǎo)的賓語(yǔ)從句時(shí)，習(xí)慣上將這些連接詞置于句首，即“連接代/副詞+do you think /believe /expect+賓語(yǔ)從句的其余部分?”如：
Who do you think is the best player this year? 你認(rèn)為今年誰(shuí)是最佳運(yùn)動(dòng)員?
What do you suppose you will do after school? 你想放學(xué)后干什么?
(4)同位語(yǔ)從句
就是在句中作同位語(yǔ)的從句。它通常有放在thought, idea, news, word(=news), plan, doubt, question, fact, suggestion, belief等抽象名詞的后面，說(shuō)明這些詞的具體內(nèi)容或含義。同位語(yǔ)從句大多由that引導(dǎo)，也可由whether, how, when, where, why等引導(dǎo)，但不能由which引導(dǎo)。如：
The idea that the earth is round is not a new one. “地球是圓的”這種觀點(diǎn)并不新鮮。
He must answer the question whether he agrees to it or not. 他必須回答他是否同意此事這們一問(wèn)題。
I have no idea when he will set out. 我不知他什么時(shí)候出發(fā)。
注：有時(shí)，同位語(yǔ)從句并不緊跟在它所說(shuō)明的詞的后面。如：
The whole truth came out at last that he was a wolf in sheep’s clothing. 真相終于大白了，他原來(lái)是一只披羊皮的狼。
