在复合句中，用一个句子来修饰名词或代词，则这个句子叫做定语从句该句子一般放在被修饰的词后面，被修饰的词叫做先行词，先行词和从句之间需要有引导词，又叫关系词（即连接词）来引导，接下来我们就来聊聊关于英语语法全掌握定语从句?以下内容大家不妨参考一二希望能帮到您!
英语语法全掌握定语从句
在复合句中，用一个句子来修饰名词或代词，则这个句子叫做定语从句。该句子一般放在被修饰的词后面，被修饰的词叫做先行词，先行词和从句之间需要有引导词，又叫关系词（即连接词）来引导。
定从引导词定语从句的引导词包括关系代词和关系副词，具体：
关系代词：that, which, who, whom, whose, as
关系副词：where, when, why
定从翻译要点将先行词放在从句后翻译，句中其它成分的翻译语序不变
eg. The first place that they visited in London was the Big Ben.
分析：此句中，the first place为先行词，that是引导词，从句部分为they visited in London,因此翻译顺序应为：they visited in London the first place was the Big Ben
所以，此句应译为：他们参观伦敦的第一个地方是大本钟。
定从用法讲解1.关系代词引导的定从：
① Who: a) 先行词必须是人 b) who代替先行词在从句中作主语。
eg. The boys who are playing football are from Class 1.
eg. Yesterday I helped an old man who lost his way.
② Whom: a) 先行词必须是人 b) whom代替先行词在从句中作宾语。c) whom代替先行词在句中作宾语时常可省略。
eg. Mr. Liu is the person (whom) you talked about on the bus.
eg. Li Ling is just the boy (whom) I want to see.
③ Which: a) 先行词必须是物 b) which 代替先行词在句中既可作主语也可作宾语（作宾语时常可省略）。
eg. This is the pen (which) I bought yesterday.
④ That: a) 先行词既可是人，也可是物（相当于who, whom, which) b) that代替先行词在句中既可作主语也可作宾语（作宾语时常可省略)。
eg. Where is the man that/whom I saw this morning?
⑤ Whose: 既可指人也可指物，在从句中作定语，一般译为“XX的 先行词”。
eg. He has a friend whose father is a doctor.
注：whose 引导的句子，先行词是物时，常可用of 结构代替：
eg. The classroom whose door is broken will be repaired soon.
=The classroom the door of which is broken will be repaired soon.
eg. Do you like the book whose cover is yellow?
=Do you like the book the cover of which is yellow?
⑥ As: 引导非限制性定语从句，代替一个句子，一般译为“正如，正像。。。”。
eg. He married her, as was natural.
注：as 引导非限制性定语从句，可放于主句之前，也可放于主句之后，甚至可以放在句中。当as 引导的从句放于主句之后时，as可以与which互换:
eg. As is known to all, China is a developing country.
eg. He was honest, as(which) we can see.
2. 介词 关系代词引导的定从：
构成：介词 whom/which
若先行词是人，则用介词 whom；若先行词是物，则用介 whom/which
eg. The school in which he once studied is very famous. (此处in which相当于where)
=1. The school is very famous. 2. He once studied in the school.
（先行词是the school-物，且因为是in the school,所以用in which)
eg. Tomorrow I will bring here a magazine, for which you asked.
=1. Tomorrow I will bring here a magazine. 2. You asked for the magazine.
（先行词是magazine-物，且因为是ask for the magazine,所以用for which)
eg. The man with whom you talked is my friend.
=1. The man is my friend. 2. you talked with the man.
（先行词是man-人，且因为是talk with the man,所以用with whom)
注：含有介词的动词短语一般补拆开，如：look for, look after, take care of...
eg. This is the watch which(that) I am looking for.
3. 关系副词引导的定从：
When: a) 先行词必须是时间名词 b) when代替先行词在从句中充当时间状语
eg. I still remember the day when I first came to the school.
Where: a) 先行词必须是地点名词 b) where 代替先行词在从句中充当地点状语
eg. Shanghai is the city where I was born.
Why: a) 先行词一般是reason b) why 代替reason在从句中充当原因状语
eg. Please tell me the reason why you missed the plane.
注:
a) 当先行词是时间/地点/原因名词时，若它在从句中充当主语或宾语，则不能用when/where/why引导，应用that/which.
eg. I won’t forget those days that(which) I spent with you.
解读：此句中，先行词是充当从句中spent的宾语，因此不能用when,而要用that/which.
eg. The school that(which) we first visited is very famous.
eg. The school where I once studied is very famous.
解读：第一句中，先行词是充当从句中visited的宾语，因此用that/which；第二句中，先行词是充当从句中的地点状语（不是I once studied the school-the school作studied的宾语, 而是I once studied in the school-the school作studied的地点状语)，因此用where.
eg. This is the reason that(which) he explained to me.
eg. This is the reason why he was late.
解读：第一句中，先行词是充当从句中explained的宾语，因此用that/which；第二句中，先行词是充当从句中的原因状语，因此用where.
Tips：定语从句中，若先行词是时间/地点/原因名词，先判断从句中当从句中是否缺主语或宾语，若既不缺主语，也不缺宾语时，则用相应的关系副词when/where/why引导；若从句中缺主语或宾语，则用which/that引导。
b) 某些关系副词引导的定从与介词 关系代词引导的定从可互换，即：where/when/why 定从=介词 关系代词 定从
eg. The year was 1932, when I arrived here.
=The year was 1932 in which I arrived here.
1. The year was 1932. 2. I arrived here in 1932
eg. This is the tower where I took a photo.
=This is the tower in front of which I took a photo.
1. This is the tower. 2. I took a photo in front of the tower.
eg. This is the reason why he was late.
=This is the reason for which he was late.
1. This is the reason. 2. He was late for the reason.
但并不是所有的介词 关系代词引导的定从都可以与关系副词引导的定从互换，如：
This is the tower about which they were just talking. (此句无法用关系副词引导的定从表示）
4. that, which引导定从时的区别：
that 和which引导定语从句时，都可以代替先行词在从句中充当主语或宾语，但which的先行词必须是物，而that的先行词既可以是人，也可以是物。当that或which代替先行词在句中作宾语时，常可省略。
eg. Where is the man that(whom) I saw this morning?
eg. This is the pen(which) I bought yesterday.
A) 只用that的情况：
a. 当先行词是不定代词（复合不定代词），如：anything, everything, nothing, something, few, all, none, little, some, any, no, much等或由不定代词any, all, some, no, little, few, much等修饰时。
eg. All that can be done has been done.
eg. There is nothing that I can do for you.
b. 当先行词被序数词修饰时。
eg. The first place that they visited in London was the Big Ben.
c. 当先行词被形容词最高级修饰时。
eg. This is the best film that I have seen.
d. 当先行词被the very, the only, the right, the next 等修饰时。
eg. This is the very dictionary that I want to buy.
e. 当先行词前有who, which等疑问代词时。
eg. Who is the man that is standing there?
f. 当先行词由两部分组成（由and连接）且这两部分包括人和物时。
eg. Can you remember the scientist and his theory that we have learned?
B) 只用which的情况：
a) 在非限制性定语从句中。
eg. China, which was founded in 1949, is becoming more and more powerful.
b) 在介词 关系代词的定语从句中。
eg. The school in which I once studied is very famous.
c) 先行词为that, those时。
eg. What’s that which is under the desk?
Note:
1. 先行词：定语从句中被修饰的名词或代词叫做先行词，一般放在引导词前面。
2. 引导词/关系词：定语从句中用来连接主句和从句的词，包括关系代词和关系副词。
3. 非限制性定语从句：定语从句有限制性和非限制性两种。限制性定语从句是先行词不可缺少的部分，去掉它主句意思往往不明确；非限制性定语从句是先行词的附加说明，去掉了也不会影响主句的意思，它与主句之间通常用逗号分开，将非限定性定语从句放在句子中间，其前后都需要用逗号隔开。
,
