主語從句，即在複合句中充當主語成分的句子，例如"That he finished writing the composition in such a short time surprised us all"，他在很短的時間內寫完作文讓我們都很驚訝，此複合句主要描述的是某事讓我們驚訝，某事就是該複合句的主語，因此“That he finished writing the composition in such a short time”便是該複合句的主語從句。
引導主語從句的連詞主要有：
從屬連詞：that whether
連線代詞：who whoever whom whose what whatever which whichever
連線副詞：when where how why
基本介紹
- 中文名：主語從句
- 外文名：Subject Clause
- 解釋：複合句中充當主語成分的句子
- 從屬連詞：that whether
主語從句,定義,第一部分,第二部分,用法,
主語從句
定義
第一部分
主語從句的時態不受主句時態的影響和限制
（1）That he finished writing the composition in such a short time surprised us all.
他在如此短的時間內寫完作文使我們十分驚訝。
（2）Whether we will go for an outing tomorrow remains unknown.
我們明天是否會去郊遊仍舊未知。
（3）Who will be our monitor hasn't been decided yet.
現在還沒有決定誰會成為我們的班長。
（4）Whom we must study for is a question of great importance.
“我們為誰而學習”是個很重要的問題。
（5）What caused the accident remains unknown.
事故的起因是未知的。
（6）Whatever you did is right.
你做的任何事都是正確的。
（7）Whom the watch belongs to is unknown.
手錶的歸屬是未知的。
（8）What we need is time.
我們需要的是時間。
（9）What we need are good doctors.
我們需要的是好的醫生。
名詞性從句的時態規則：
1）、主句謂語動詞是現在或將來時，從句謂語動詞可以用任何需要的時態。
I wonder what he is doing now.
I wonder what he is doing now.
我想知道他現在在乾什麼。
Do you know when and where he was born?
Do you know when and where he was born?
你知道他在何時何地出身嗎？
I'll write to tell him where I 'll meet him.
I'll write to tell him where I 'll meet him.
我將寫信告訴他我將在哪裡與他碰面。
2）、主句謂語動詞是過去時，從句謂語動詞一般需用過去時。
（1）從句與主句的謂語動作同時發生，從句用一般過去時或過去進行時。
I thought that he studied hard.
I thought that he studied hard.
我認為他學習很努力。
He told me his son was watching TV.
He told me his son was watching TV.
他告訴我他的兒子在看電視。
（2）從句謂語動作在主句謂語動作之後，從句用過去將來時。
He said he would spend his holidays in Qingdao.
He said he would spend his holidays in Qingdao.
他告訴我他將在青島度假。
（3）從句謂語動作在主句謂語動作之前，從句用過去完成時。
They told me they had waited for me half an hour.
They told me they had waited for me half an hour.
他們告訴我他們已經等了我半小時了。
（4）從句如果有表示過去某一具體時間的狀語，仍用過去時。
She told me her brother died in 1945.
She told me her brother died in 1945.
她告訴我她的哥哥（弟弟）死於1945年。
3)從句時態不受下列客觀的條件影響。
（1）從句說明的是不受時間限制的事實或真理（客觀真理）。
The teacher told us that the earth turns from west to east.
老師告訴我們地球自西向東轉。
He said Asia is the largest continent.
He said Asia is the largest continent.
他說亞洲是最大的大陸。
It was true that water freezes at thirty-two degrees Fahrenheit.
水在的確是在32華氏度結凍的。
（2）當從句表示的是反覆出現的時態不變。
（2）當從句表示的是反覆出現的時態不變。
She told me that she gets up at six o'clock every morning.
她告訴我她每天早晨6點起床。
He asked me when the train usually starts.
He asked me when the train usually starts.
他向我詢問火車通常何時出發。
（3）當從句的謂語動作仍在繼續時，或者表示現在仍在的狀態時，時態不變。
（3）當從句的謂語動作仍在繼續時，或者表示現在仍在的狀態時，時態不變。
He said that the workers in that factory are trying to fulfill the task in time.
他說那家公司的員工正在全力及時完成任務。
She told me the other day that she is only 10.
她告訴我那天她只有10歲。
（4）當從句的動作狀態還未發生，要用一般式表示。強調與現在的聯繫。
He said he will wait for me this evening.
他說他今晚將等待我。
She told me the other day that she is only 10.
她告訴我那天她只有10歲。
（4）當從句的動作狀態還未發生，要用一般式表示。強調與現在的聯繫。
He said he will wait for me this evening.
他說他今晚將等待我。
小結:
（2）連詞位於句首不能省略
（3）主語從句大多數情況下視為第三人稱單數，但也有例外，如例（9）
注意：當what引導的名詞性分句作主語時，主謂一致問題極為複雜。著名學者周海中教授在論文《關於what-分句作主語的主謂一致問題》中就這一問題做了深入研究，並給出了10種的主謂一致關係。這些一致關係值得英語學習者和使用者特別注意。
第二部分
（1）It is certain that he will win the match.
他一定會贏得這場比賽的。
（2）It is true that he has made a very important discovery in chemistry.
他的確在化學領域有了一個偉大的發現。
（3）It is very likely that they will hold a meeting.
他們很有可能會舉行一場會議。
（4）It is strange that he should do that.
他竟然那樣做是很奇怪的。
（5）It is important that we all should attend the meeting.
重要的是我們都應該參加會議。
（6）It is strange that the man should have stuck to his silly ideas.
真奇怪，這個人竟然堅持自己愚蠢的想法。
（7）It is a pity that we won't be able to go to the south to spend our summer vacation.
真遺憾我們不能去南方度過我們的暑假。
（8）It is still a mystery what caused the accident.
造成事故的原因仍舊是個秘密。
（9）It is said that he has gone to shanghai.(=He is said to have gone to shanghai)
據說他已經去上海了。
（10）It is known to all that the gun powder was first invented by the Chinese.
所有人都知道火藥最初是由中國人發明的。
（11）It is suggested that the work should be done with great care.
建議工作應該被小心地被完成。
（12）It happened that the two cheats were there. (=The two cheats happened to be there)
兩個騙子碰巧在那裡。
兩個騙子碰巧在那裡。
小結:
用法
一．主語從句
主語從句 定義：在句子中擔當主語的是一個從句，這個從句就叫做主語從句。
1. It 作形式主語和it引導強調句的比較
①主語從句常用it作形式主語，一般常用句型為：It is+{名詞/形容詞/過去分詞}+主語從句例如：
It is still a question whether she will come or not.
It is strange that you should like him.
It is still unknown which team will win the match.
另外，還有一些比較多見的結構：
It turned out that……;
It has been proved that……;
It happened/occurred that……;
It is well-known that……等等
②而強調句則不同，它的結構是：It+be+被強調部分+that+從句
強調賓語：It is English that Prof.Lin teaches us.
強調狀語：It was in shanghai that I saw the film.
判斷是否是強調句有一個方法，就是將that以後的“句子的其餘部分”拿出來單獨看，看有沒有缺成分，缺的是什麼成分，再把謂語動詞後面that前面的那部分，帶到你認為缺成分的地方，如果放進去是一句完整的句子了，那就說明是強調句。
2. 用it 作形式主語的結構
(1) It is +名詞+that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+that從句
It is natural that… 很自然……
It is strange that… 奇怪的是……
(3) it +不及物動詞+that從句
It seems that… 似乎……
It happened that… 碰巧……
(4) it is+過去分詞+that從句
It is reported that… 據報導……
It has been proved that… 已證實……
3.主語從句不可位於句首的五種情況
(1) if引導的主語從句不可居於複合句句首。
(2) It is said , (reported) …結構中的主語從句不可提前。例如：
It is said that President Jingo will visit our school next week.
(3) It happens…, It occurs… 結構中的主語從句不可提前。例如：
It occurred to him that he failed in the examination.
(4) It doesn’t matter how/whether …結構中的主語從句不可提前。例如：
It doesn’t matter whether he is wrong or not..
(5) 含主語從句的複合句是疑問句時，主語從句不可提前。例如：
Is it likely that it will rain in the evening?
4. What 與that 在引導主語從句時的區別
What you said yesterday is right.
1、引導詞：what\which\whose\when\whether\if\where
2語序：賓語從句必須是用陳述語句。（名詞性從句都是陳述語序）
如：I think that you must work harder.
