主語(yǔ)從句是在復(fù)合句中充當(dāng)主語(yǔ)的從句，通常放在主句謂語(yǔ)動(dòng)詞之前或由形式主語(yǔ)it代替，而本身放在句子末尾。
1. It 作形式主語(yǔ)和it引導(dǎo)強(qiáng)調(diào)句的比較
It 作形式主語(yǔ)代替主語(yǔ)從句，主要是為了平衡句子結(jié)構(gòu)，主語(yǔ)從句的連接詞沒(méi)有變化。而it引導(dǎo)的強(qiáng)調(diào)句則是對(duì)句子某一部分進(jìn)行強(qiáng)調(diào)，無(wú)論強(qiáng)調(diào)的是什么成分，都可用連詞that。被強(qiáng)調(diào)部分指人時(shí)也可用who/whom。例如：
a) It is a pity that you didn’t go to see the film. 你不去看那場(chǎng)電影真可惜。
b) It doesn’t interest me whether you succeed or not. 我對(duì)你成功與否不感興趣。
c) It is in the morning that the murder took place. 謀殺案是在早上發(fā)生的。(強(qiáng)調(diào)句型)
d) It is John that broke the window. 是John打碎的窗戶。(強(qiáng)調(diào)句型)
2. 用it 作形式主語(yǔ)的結(jié)構(gòu)
(1) It is + 名詞 + 從句
It is a fact that … 事實(shí)是…
It is an honor that …非常榮幸
It is common knowledge that …是常識(shí)
(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(dòng)詞 + 從句
It seems that… 似乎…
It happened that… 碰巧…
It appears that… 似乎…
(4) It + 過(guò)去分詞 + 從句
It is reported that… 據(jù)報(bào)道…
It has been proved that… 已證實(shí)…
It is said that… 據(jù)說(shuō)…
3. 主語(yǔ)從句不可位于句首的五種情況：
(1)if 引導(dǎo)的主語(yǔ)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(yǔ)從句不可提前。例如：
正確表達(dá)：It is said that President Jiang will visit our school next week.
錯(cuò)誤表達(dá)：That President Jiang will visit our school next week is said.
(3)It happens/occurs…結(jié)構(gòu)中的主語(yǔ)從句不可提前。例如：
正確表達(dá)：It occurred to him that he failed in the examination.
錯(cuò)誤表達(dá)：That he failed in the examination occurred to him.
(4)It doesn’t matter how/whether …結(jié)構(gòu)中的主語(yǔ)從句不可提前。例如：
正確表達(dá)：It doesn’t matter whether he is wrong or not.
錯(cuò)誤表達(dá)：Whether he is wrong or not doesn’t matter.
（5)含主語(yǔ)從句的復(fù)合句是疑問(wèn)句時(shí)，主語(yǔ)從句不可提前。例如：
正確表達(dá)：Is it likely that it will rain in the evening?
錯(cuò)誤表達(dá)：Is that will rain in the evening likely?
4. what 與that 在引導(dǎo)主語(yǔ)從句時(shí)的區(qū)別
what 引導(dǎo)主語(yǔ)從句時(shí)在句時(shí)在從句中充當(dāng)句子成分，如主語(yǔ).賓語(yǔ).表語(yǔ)，而that 則不然。例如：
a) What you said yesterday is right.
b) That she is still alive is a consolation
1. It 作形式主語(yǔ)和it引導(dǎo)強(qiáng)調(diào)句的比較
It 作形式主語(yǔ)代替主語(yǔ)從句，主要是為了平衡句子結(jié)構(gòu)，主語(yǔ)從句的連接詞沒(méi)有變化。而it引導(dǎo)的強(qiáng)調(diào)句則是對(duì)句子某一部分進(jìn)行強(qiáng)調(diào)，無(wú)論強(qiáng)調(diào)的是什么成分，都可用連詞that。被強(qiáng)調(diào)部分指人時(shí)也可用who/whom。例如：
a) It is a pity that you didn’t go to see the film. 你不去看那場(chǎng)電影真可惜。
b) It doesn’t interest me whether you succeed or not. 我對(duì)你成功與否不感興趣。
c) It is in the morning that the murder took place. 謀殺案是在早上發(fā)生的。(強(qiáng)調(diào)句型)
d) It is John that broke the window. 是John打碎的窗戶。(強(qiáng)調(diào)句型)
2. 用it 作形式主語(yǔ)的結(jié)構(gòu)
(1) It is + 名詞 + 從句
It is a fact that … 事實(shí)是…
It is an honor that …非常榮幸
It is common knowledge that …是常識(shí)
(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(dòng)詞 + 從句
It seems that… 似乎…
It happened that… 碰巧…
It appears that… 似乎…
(4) It + 過(guò)去分詞 + 從句
It is reported that… 據(jù)報(bào)道…
It has been proved that… 已證實(shí)…
It is said that… 據(jù)說(shuō)…
3. 主語(yǔ)從句不可位于句首的五種情況：
(1)if 引導(dǎo)的主語(yǔ)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(yǔ)從句不可提前。例如：
正確表達(dá)：It is said that President Jiang will visit our school next week.
錯(cuò)誤表達(dá)：That President Jiang will visit our school next week is said.
(3)It happens/occurs…結(jié)構(gòu)中的主語(yǔ)從句不可提前。例如：
正確表達(dá)：It occurred to him that he failed in the examination.
錯(cuò)誤表達(dá)：That he failed in the examination occurred to him.
(4)It doesn’t matter how/whether …結(jié)構(gòu)中的主語(yǔ)從句不可提前。例如：
正確表達(dá)：It doesn’t matter whether he is wrong or not.
錯(cuò)誤表達(dá)：Whether he is wrong or not doesn’t matter.
（5)含主語(yǔ)從句的復(fù)合句是疑問(wèn)句時(shí)，主語(yǔ)從句不可提前。例如：
正確表達(dá)：Is it likely that it will rain in the evening?
錯(cuò)誤表達(dá)：Is that will rain in the evening likely?
4. what 與that 在引導(dǎo)主語(yǔ)從句時(shí)的區(qū)別
what 引導(dǎo)主語(yǔ)從句時(shí)在句時(shí)在從句中充當(dāng)句子成分，如主語(yǔ).賓語(yǔ).表語(yǔ)，而that 則不然。例如：
a) What you said yesterday is right.
b) That she is still alive is a consolation