導語：為了解決大家的疑問，小編特地為大家整理了“定語從句和主語從句”相關內容，僅供參考!
一．主語從句
主語從句是在複合句中充當主語的從句，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引導強調句的比較
It 作形式主語代替主語從句，主要是為了平衡句子結構，主語從句的連線詞沒有變化。而it引導的強調句則是對句子某一部分進行強調，無論強調的是什麼成分，都可用連詞that。被強調部分指人是也可用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 作形式主語的結構
(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… 據報道… 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. (right) That President Jiang will visit our school next week is said. (wrong) (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. (right) That he failed in the examination occurred to him. (wrong) (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. (right) Whether he is wrong or not doesn’t matter. (wrong) (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? (right) Is that will rain in the evening likely? (wrong)
4. What 與that 在引導主語從句時的區別
What 引導主語從句時在句時在從句中充當句子成分，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.
二、定語從句
定語從句是由關係代詞和關係副詞引導的從句，其作用是作定語修飾主句的某個名詞性成分，定語從句分為限定性和非限定性從句兩種。
（一） 限定性定語從句
1. that即可代表事物也可代表人，which代表事物；它們在從句中作主語或賓語，that在從句中作賓語時常可省略關係詞，which在從句中作賓語則不能省略。而且，如果which在從句中作“不及物動詞＋介詞”的`介詞的賓語，注意介詞不要丟掉，而且介詞總是放在關係代詞which的前邊，但有的則放在它原來的位置。
2. which作賓語時，根據先行詞與定語從句之間的語義關係，先行詞與which之間的介詞不能丟。
3. 代表物時多用which，但在帶有下列詞的句子中用that而不用which，這些詞包括all, anything, much等，這時的that常被省略
4. who和whom引導的從句用來修飾人，分別作從句中的主語和賓語，whom作賓語時，要注意它可以作動詞的賓語也可以作介詞的賓語
5. where是關係副詞，用來表示地點的定語從句
6. when引導定語從句表示時間［注］值得一提的是，表示時間“time
7. whose是關係代詞，修飾名詞作定語，相當於所修飾成分的前置所有格
8. 當從句的邏輯主語是some, any, no, somebody, anybody, nobody, something, anything, everything或nothing時，常用there is來引導。
（二）非限定性定語從句：
非限定性定語從句的作用是對所修飾的成分作進一步說明，通常和主句間用逗號隔開，將從句拿掉後其他部分仍可成立
1. which引導的非限定性定語從句來說明前面整個句子的情況或主句的某一部分
2. 在引導限定性定語從句時，that有時相當於in which, at which, for which或at which Attitudes towards daydreaming are changing in much the same way that(in which) attitudes towards night dreaming have changed. 人們對白日做夢的態度正在改變，這與人們對夜間做夢的看法的變化有非常相似之處。 I like the music for the very reason that(for which) he dislike it. 我出於某種原因喜歡這種音樂，而他恰恰與我相反。 We arrived the day that(on which) they left. 剛好我們到的那天他們走了。
3. 有時as也可用作關係代詞 4. 在非限定性定語從句中，不能用that，而用who, whom代表人，用which代表事物.
定語從句及相關術語
1.定語從句：修飾一個名詞或代詞的從句稱為定語從句，一般緊跟在它所修飾的先行詞後面。
2.關係詞：引導定語從句的關聯詞成為關係詞關係詞有關係代詞和關係副詞。關係代詞有that, which, who, whom, whose, as等；關係副詞有where, when, why等。關係詞常有3個作用：1，引導定語從句。2，代替先行詞。3，在定語從句中擔當一個成分。
二.關係代詞引導的定語從句
指人，在從句中做主語(1) The boys who are playing football are from Class One.(2) Yesterday I helped an old man who lost his way.
2. whom指人，在定語從句中充當賓語，常可省略。(1) Mr. Liu is the person (whom) you talked about on the bus.(2) Mr. Ling is just the boy whom I want to see.注意：關係代詞whom在口語和非正式語體中常用who代替，可省略。(3) The man who/whom you met just now is my friend.
3. which指物，在定語從句中做主語或者賓語，做賓語時可省略(1) Football is a game which is liked by most boys.(2) This is the pen (which) he bought yesterday. 如果在從句中做賓語,就用whom或who.比如: He is the man whom/who I talk to. 如果是在從句中作主語就只能用who.比如: He is the man who has an English book.
4. that指人時，相當於who或者whom；指物時，相當於which。在定語從句中做主語或者賓語，做賓語時可省略。(5) The number of the people that/who come to visit the city each year rises one million.(6) Where is the man that/whom I saw this morning?
5. whose通常指人，也可指物，在定語從句中做定語(1) He has a friend whose father is a doctor.(2) I once lived in a house whose roof has fallen e指物時，常用以下結構來代替
(3) The classroom whose door is broken will soon be repaired.(4) The classroom the door of which is broken will soon be repaired.(5) Do you like the book whose cover is yellow?(6) Do you like the book the color of which is yellow?
