定语从句和主语从句
一．主语从句
主语从句是在复合句中充当主语的从句，通常放在主句谓语动词之前或由形式主语it代替，而本身放在句子末尾。
1. It 作形式主语和it引导强调句的比较
It 作形式主语代替主语从句，主要是为了平衡句子结构，主语从句的连接词没有变化。而it引导的强调句则是对句子某一部分进行强调，无论强调的是什么成分，都可用连词that。被强调部分指人是也可用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 作形式主语的结构
(1) It is ＋名敏伍词＋从句 It is a fact that … 事实是… It is an honor that …非常荣幸 It is common knowledge that …是常识 (2) it is ＋形容词＋从句 It is natural that… 很自然… It is strange that… 奇怪的是… (3) it is ＋不及物动词＋从句 It seems that… 似乎… It happened that… 碰巧… (4) it ＋过去分词＋从句 It is reported that… 据报道… It has been proved that… 已证实…
3. 主语从句不可位于句首的五种情况
(1) if 引导的主语从句不可居于复合句句首吵拿行。 (2) It is said , (reported) …结构中的主语从句不可提前。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… 结构中的'主语从句不可提前。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 …结构中的主语从句不可提前。例如： It doesn’t matter whether he is wrong or not. (right) Whether he is wrong or not doesn’t matter. (wrong) (5) 含主语从句的复合句是疑问句时，主语从句不可提前。例如： Is it likely that it will rain in the evening? (right) Is that will rain in the evening likely? (wrong)
4. What 与that 在引导主语从句时的区别
What 引导主语从句时在句时在从句中充当句子成分，如主语．宾语．表语，而that 则不然。例如： 1) What you said yesterday is right. 2) That she is still alive is a consolation.
二、定语从句
定语从句是由关系代词和关系副词引导的从句，其作用是作定语修饰主句的某个名词性成分，定语从句分升哗为限定性和非限定性从句两种。
（一） 限定性定语从句
1. that即可代表事物也可代表人，which代表事物；它们在从句中作主语或宾语，that在从句中作宾语时常可省略关系词，which在从句中作宾语则不能省略。而且，如果which在从句中作“不及物动词＋介词”的介词的宾语，注意介词不要丢掉，而且介词总是放在关系代词which的前边，但有的则放在它原来的位置。
2. which作宾语时，根据先行词与定语从句之间的语义关系，先行词与which之间的介词不能丢。
3. 代表物时多用which，但在带有下列词的句子中用that而不用which，这些词包括all, anything, much等，这时的that常被省略
4. who和whom引导的从句用来修饰人，分别作从句中的主语和宾语，whom作宾语时，要注意它可以作动词的宾语也可以作介词的宾语
5. where是关系副词，用来表示地点的定语从句
6. when引导定语从句表示时间［注］值得一提的是，表示时间“time
7. whose是关系代词，修饰名词作定语，相当于所修饰成分的前置所有格
8. 当从句的逻辑主语是some, any, no, somebody, anybody, nobody, something, anything, everything或nothing时，常用there is来引导。
（二）非限定性定语从句：
非限定性定语从句的作用是对所修饰的成分作进一步说明，通常和主句间用逗号隔开，将从句拿掉后其他部分仍可成立
1. which引导的非限定性定语从句来说明前面整个句子的情况或主句的某一部分
2. 在引导限定性定语从句时，that有时相当于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. 人们对白日做梦的态度正在改变，这与人们对夜间做梦的看法的变化有非常相似之处。 I like the music for the very reason that(for which) he dislike it. 我出于某种原因喜欢这种音乐，而他恰恰与我相反。 We arrived the day that(on which) they left. 刚好我们到的那天他们走了。
3. 有时as也可用作关系代词 4. 在非限定性定语从句中，不能用that，而用who, whom代表人，用which代表事物.
定语从句及相关术语
1.定语从句：修饰一个名词或代词的从句称为定语从句，一般紧跟在它所修饰的先行词后面。
2.关系词：引导定语从句的关联词成为关系词关系词有关系代词和关系副词。关系代词有that, which, who, whom, whose, as等；关系副词有where, when, why等。关系词常有3个作用：1，引导定语从句。2，代替先行词。3，在定语从句中担当一个成分。
二.关系代词引导的定语从句
1.who指人，在从句中做主语(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，在定语从句中充当宾语，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：关系代词whom在口语和非正式语体中常用who代替，可省略。(3) The man who/whom you met just now is my friend.
3. which指物，在定语从句中做主语或者宾语，做宾语时可省略(1) Football is a game which is liked by most boys.(2) This is the pen (which) he bought yesterday. 如果在从句中做宾语,就用whom或who.比如: He is the man whom/who I talk to. 如果是在从句中作主语就只能用who.比如: He is the man who has an English book.
4. that指人时，相当于who或者whom；指物时，相当于which。在定语从句中做主语或者宾语，做宾语时可省略。(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，在定语从句中做定语(1) He has a friend whose father is a doctor.(2) I once lived in a house whose roof has fallen in.whose指物时，常用以下结构来代替
(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?
