全力直擊英語語法：名詞性從句

名詞性從句是由if, whether, that 和各種疑問詞充當(dāng)連接詞所引導(dǎo)的從句，其功同名詞一樣。

一．主語從句

主語從句是在復(fù)合句中充當(dāng)主語的從句，通常放在主句謂語動詞之前或由形式主語it代替，而本身放在句子末尾。

1. It 作形式主語和it引導(dǎo)強調(diào)句的比較

It 作形式主語代替主語從句，主要是為了平衡句子結(jié)構(gòu)，主語從句的連接詞沒有變化。而it引導(dǎo)的強調(diào)句則是對句子某一部分進行強調(diào)，無論強調(diào)的是什么成分，都可用連詞that。被強調(diào)部分指人是也可用who/whom。例如：

It is a pity that you didn‘t go to see the film.

It doesn‘t interest me whether you succeed or not.

It is in the morning that the murder took place.

It is John that broke the window. 

2. 用it 作形式主語的結(jié)構(gòu)

(1) It is ＋名詞＋從句

It is a fact that …事實是…

It is an honor that…非常榮幸

It is common knowledge that…是常識

(2) it is ＋形容詞＋從句

It is natural that…很自然…

It is strange that…奇怪的是…

(3) it is ＋不及物動詞＋從句

It seems that…似乎…

It happened that…碰巧…

(4) it ＋過去分詞＋從句

It is reported that…據(jù)報道…

It has been proved that…已證實…

3. 主語從句不可位于句首的五種情況

(1) if 引導(dǎo)的主語從句不可居于復(fù)合句句首。

(2) It is said , (reported) …結(jié)構(gòu)中的主語從句不可提前。例如：

It is said that President Jingo will visit our school next week. (right)

That President Jiang will visit our school next week is said. (wrong)

(3) It happens…, It occurs… 結(jié)構(gòu)中的主語從句不可提前。例如：

It occurred to him that he failed in the examination. (right)

That he failed in the examination occurred to him. (wrong)

(4) It doesn‘t matter how/whether …結(jié)構(gòu)中的主語從句不可提前。例如：

It doesn‘t matter whether he is wrong or not. (right)

Whether he is wrong or not doesn‘t matter. (wrong)

(5) 含主語從句的復(fù)合句是疑問句時，主語從句不可提前。例如：

Is it likely that it will rain in the evening? (right)

Is that will rain in the evening likely? (wrong)

4. What 與that 在引導(dǎo)主語從句時的區(qū)別

What 引導(dǎo)主語從句時在句時在從句中充當(dāng)句子成分，如主語．賓語．表語，而that 則不然。例如：

1) What you said yesterday is right.

2) That she is still alive is a consolation.