（一）限制性定语从句中只能用that 引导定语从句的情况
1．当先行词是everything, anything, nothing (something 除外), all, none, few, little, some等代词时，或当先行词受every, any, all, some, no, little, few, much等代词修饰时。如：
Have you taken down everything that Mr. Li said? 李老师讲的你都记下来了吗？
There seems to be nothing that is impossible to him in the world. 对他来说似乎世界上没有什么不可能的事。
All that can be done has been done. 所有能做的都做好了。
There is little that I can do for you. 我不能为你干什么。
He stayed in the library and looked up any information that they needed. 他呆在图书馆查找所需的资料。
注意：当先行词指人时，偶尔也可用关系代词who，如：
Any man that / who has a sense of duty won’t do such a thing. 任何有责任感的人都不会做这样的事。
All the guests that / who were invited to her wedding were important people. 所有应邀来参加她婚礼的客人都是重要人物。
2．当先行词被序数词修饰时。如：
The first place that they visited in London was the Big Ben. 在伦敦他们参观的第一个地方是大本钟。
3．当先行词被形容词最高级修饰时。如：
This is the best film that I have ever seen. 这是我看过的最好的电影。
4．当先行词被the very, the only修饰时。如：
This is the very dictionary that I want to buy. 这正是我要买的词典。
After the fire in his house, the old car is the only thing that he owns. 家里发生了火灾过后，那辆旧车成了他的唯一拥有。
注意：当先行词指人时，偶尔也可用关系代词who。如：
Wang Hua is the only person in our school who will attend the meeting. 王华是我校唯一出席会议的人。
5．当先行词前面有who, which等疑问代词时。如：
Who is the man that is standing by the gate? 站在门口的那个人是谁？
Which is the T-shirt that fits me most? 哪件T恤衫最合我的身？
6．当先行词为人与动物或人与物时。如：
They talked about the persons and things that they remembered at school 他们谈论着他们所能记起的在校时的人和事。
Look at the man and his donkey that are walking up the street. 瞧瞧那个沿街走来的人和他的 毛驴。
（二）关系代词as和which 引导的定语从句
as 和which 引导非限制性定语从句时， 其用法有相同之处，也有不同之处。具体情况是：
1. as 和which都可以在定语从句中做主语或宾语，代表前面整个句子。如：
He married her, as / which was natural. 他跟她结婚了，这是很自然的事。
He is honest, as / which we can see. 他很诚实， 这一点我们看得出来。
2. as 引导的非限制性定语从句可以放在主句之前、主句之后，甚至还可以分割主句。 which 引导的非限制性定语从句只可放在主句之后。另外，as 常常有“正如、正像”的含义。如：
As is known to all, China is a developing country. 众所周知，中国是发展中国家。
He is from the south, as we can know from his accent. 他是南方人，这一点我们从他的口音可以知道。
John, as you know, is a famous writer. 正如你所知， 约翰是个著名作家。
Zhang Hua has been to Paris more than ten times, which I don’t believe. 张华已去过巴黎十多次了，这一点我不相信。
注意：当主句和从句之间存在着逻辑上的因果关系时，关系词往往只用which。如：
Tom was late for school again and again, which made his teacher very angry. 汤姆老是迟到，这使得老师很恼火。
These tables are made of metal, which made them very heavy. 这些桌子是金属的，这使得这些桌子很重。
1. 当先行词受such, the same 修饰时，关系词常用as。 如：
I’ve never heard such stories as he tells. 我从未听过象他讲的这样的故事。
He is not such a fool as he looks. 他可不象他看上去的那样傻。
This is the same dictionary as I lost last week. 这部词典跟我上星期丢失的一样。
注意：当先行词受the same 修饰时，偶尔也用 that引导定语从句，但与as引导的定语从句意思有区别。如：
She wore the same dress that she wore at Mary’s wedding. 她穿着她在玛丽婚礼上穿过的同一条连衣裙。
She wore the same dress as her younger sister wore. 她穿着跟她妹妹所穿的一样的连衣裙。
(三) 以the way为先行词的限制性定语从句通常由in which或that引导，而且通常可以省略。如：
The way (that / in which ) he answered the questions was surprising. 他回答这些问题的方式令人惊奇。
I don’t like the way (that / in which) you laugh at her. 我不喜欢你冲她的样子。
（四）关系代词与关系副词的选择
用关系代词还是关系副词引导定语从句主要看关系词在定语从句中的作用（即所担当的成分）。试比较：
A. I know a place where we can have a picnic. 我知道一个我们可以野炊的地方。
I know a place which / that is famous for its beautiful natural scenery. 我知道一个以自然景色优美而闻名的地方。
B. I will never forget the days when we spent our holidays together. 我永远忘不了我们一起度假的日子。
I will never forget the days that / which we spent together. 我永远忘不了我们一起度过的日子。
C. This is the reason why he was dismissed. 这就是他被解雇的原因。
This is the reason that / which he explained to me for his not attending the meeting. 这就是他向我解释的他没有参加会议的原因。
（五）but 有时也用作关系词引导定语从句。如：
There are very few but admire his talents. 很少有人不赞赏他的才干的。（but = who don’t）
（六）定语从句与同位语从句的区别
1．定语从句修饰限定先行词，它与先行词是修饰关系；同位语从句说明先行词的具体内容，它与先行词是同位关系。
The plane that has just taken off is for Paris. （定语从句） 刚刚起飞的那架飞机是开往巴黎的。
The fact that he has already died is quite clear. （同位语从句） 他已经去世了，这个事实很明了。
2．定语从句由关系代词或关系副词引导，关系词在从句中担当相应的句子成分，关系代词在从句中作宾语时经常可省略。同位语从句主要由连词that 引导，在从句中一般不担当成分；有时也由where, when, how, who, whether, what 等连词引导，这些连词则在从句中担当成分。
The news that he told me is true. （定语从句） 他告诉我的消息是真的。
The news that he has just died is true. （同位语从句） 他刚刚去世了，这个消息是真的。
The problem that we are facing now is how we can collect so much money. (定语从句) 我们现在面临的问题是如何筹集这么多资金。
The problem how we can collect so much money is difficult to solve. （同位语从句） 我们如何筹集这么多资金，这个问题很难解决。
The question that he raised puzzled all of us. （定语从句） 他提出的问题让我们很为难。
The question whether he is sure to win the game is hard to answer. （同位语从句） 他是否一定会赢得那场比赛，这个问题很难回答。
3．同位语从句与先行词一般可以用动词be发展成一个完整的句子, 而定语从句则不能。如：
A. The idea that he we could ask the teacher for advice is wonderful. （同位语从句）我们可以向老师请教，这个主意不错。
The idea was that we could ask the teacher for advice.
B. The fact that the earth moves around the sun is known to all. （同位语从句） 地球围绕太阳转，这个事实人人皆知。
The fact is that the earth moves around the sun.
C. Pay attention to the problem how we can protect the wild animals. （同位语从句） 请注意如何保护野生动物这个问题。
The problem is how we can protect the wild animals.
（6）不定式的构成
1. 不定式的构成
不定式是由不定式符号to+动词原形构成，在某些情况下to也可省略。
不定式一般有时式和语态的变化，通常有下表中的几种形式（以do为例）：
主动式
被动式
一般式
to do
to be done
完成式
to have done
to have been done
进行式
to be doing
/
完成进行式
to have been doing
/
1) 不定式的一般式
不定式的一般式所表示的动作通常与主要谓语的动作同时或几乎同时发生，或是在它之后发生。如：
They invited us to go there this summer. 他们邀请我们今年夏天去那儿。
He stood aside for me to pass. 他站到一边让我通过。
2) 不定式的完成式
不定式的完成式所表示的动作在谓语所表示的动作之后发生，它在句中可作表语、状语、宾语，有时也可作主语、定语等。如：
She seemed to have heard about this matter. 她似乎已听说过这件事。
I am sorry to have kept you waiting so long. 我很抱歉让你等了这么久。
I meant to have told you about it, but I happened to have an important thing to do.
我本来想告诉你这件事的，但我碰巧有一件重要的事要做。
It has been an honor for me to have traveled so much in your country.
对我来说，在你们国家旅行这么多地方是一件很荣幸的事情。
3) 不定式的进行式
不定式的进行式表示正在进行的与谓语动词同时发生的动作。它在句中可以用作除谓语以外的所有成分。如：
It’s nice of you to be helping us these days. 你真好，这些天一直帮我们。
He pretended to be listening to the teacher carefully. 他假装在认真地听老师讲课。
We didn’t expect you to be waiting for us here. 我们没料到你一直在这儿等我们。
4) 不定式的完成进行式
如果不定式表示的动作是谓语所表示时间之前一直进行的动作，就需要用完成进行式。如：
They are said to have been working in Tibet for 20 years. 据说他们已经在西藏工作20年了。
We are happy to have been helping each other these days. 我们很高兴这些天能互相帮助。
5) 动词不定式的否定形式是由not或never加不定式构成。如：
Try not to be late again next time. 尽量下次不要再迟到。
He wished us never to meet her again. 他希望我们永远不要再见到她。
6) 疑问词+动词不定式：
不定式和疑问词whether, what, which, whom, where, when, how, why等连用可以在句中起名词的作用，通常跟在tell, know, show, decide, learn, wonder, explain, advise, teach, discuss, find out等动词后面作宾语，有时也可以充当主语、表语等。如：
On hearing the news, he didn’t know whether to laugh or to cry.
听到这个消息，他不知道该哭还是该笑。
When to hold the meeting has not decided. 什么时候开会还没有决定。
The most important problem is how to get so much money.
最重要的事情是如何搞到这么多钱。
介词后一般不直接接不定式，但可以接疑问词+不定式短语作宾语。如：
Mary gave some advice on how to learn English. 玛丽提了一些如何学习英语的建议。
I have no idea of how to do it. 我不知道该怎么做。
7) 不定式的被动式：
当不定式逻辑上的主语是这个不定式所表示的动作的承受者时，不定式一般要用被动形式，to be +过去分词和to have been +过去分词。这些形式可以用来作主语、表语、宾语、定语、状语、补语。如：
It’s a good thing for him to have been scolded by the teacher. 对他来说，被老师责备是一件好事。
They seemed to be satisfied with the result. 他们似乎对结果很满意。
He asked to be sent to work in the countryside. 他要求被派往农村工作。
She was the last person to have been mentioned at the meeting.
她是会上最后一个被提到的人。
I had to shout to be heard. 我不得不大喊才能被听到。
We don’t like our friends to be laughed at from time to time. 我们不喜欢我们的朋友不时地被嘲笑。
2. 不定式的语法作用
1) 不定式作主语：
To see once is better than to hear a hundred times. 百闻不如一见。
To master a foreign language is not an easy thing. 掌握一门外语不是一件容易的事。
在很多情况下，人们通常用it作为形式上的主语，而把不定式短语移到谓语之后，使句子显得平稳一些。如：
It’s good manners to wait in line. 排队等候是很有礼貌的。
It made us very angry to hear him speak to his mother like that. 听到他那样跟他妈妈说话我们很生气。
2) 不定式作表语：
The most important thing is to put theory into practice. 最重要的事情是把理论付诸实践。
The greatest happiness is to work for the happiness of all. 最大的幸福就是为大家的幸福而工作。
3) 不定式作宾语：
He wanted to know the truth. 他想知道真相。
I prefer to be starved to death rather than beg. 我宁愿被饿死也不愿乞讨。
He pretended to have read the book when I asked him about it.
我问到他的时候，他假装读过这本书。
另外，不定式在某些复合宾语中作宾语时，人们常常用it代表不定式，而将真实宾语放在补足语之后。如：
Do you think it better to translate it in this way? 你认为这样翻译是不是更好？
I feel it a great honor to be invited to speak at the meeting before so many students.
我觉得被邀请在会上面对这么多学生发言是一件很光荣的事情。
4) 不定式作补语：
①不定式可以和名词或代词一起构成复合结构作动词的宾语，这时不定式被称为宾语补足语。如：
I would like you to help me with my English exercises. 我想请你帮我做英语练习。
I never expected the shoes to be worn out so soon. 我从来没想到鞋子这么快就穿破了。
注意：动词help后面接不定式作宾语或宾语补足语可以带to也可以不带to。如：
Who can help me (to) carry this heavy box? 谁能帮我拎这个重箱子？
②在make, let, have等使役动词和see, watch, notice, hear, feel等感官动词后的复合宾语中，动词不定式不带to。
I often hear her sing in the next room. 我经常听到她在隔壁唱歌。
They make the baby go to bed at 7:00 p.m. every day. 他们每天让孩子晚上7：00上床睡觉。
注意：get, leave等词也有“让”“叫”的意思，和使役动词意思相近，但它们后面的不定式作宾语补足语必须要有to。如：
I’ll get him to try it again. 我将让他再试一次。
How could you leave him to have supper with a stranger?
你怎么让他跟一个陌生人一起吃晚饭？
注意：当使役动词和感官动词变为被动语态时，不定式就成了主语补语，作主语补语的不定式必须加to。如：
Though he had often made his little sister cry, today he was made to cry by his little sister. 尽管他经常弄哭他的小妹妹，但今天他却被他的小妹妹弄哭了。
He is often heard to sing the song. 经常有人听到他唱这首歌。
③think, consider, believe, declare, suppose, find, imagine, know, understand, take, prove, feel等动词后面接的不定式短语作补语多由to be+形容词或名词构成，think, consider, find后的to be常可省略。如：
When he woke up, she found herself (to be ) badly injured.
她醒来的时候，发现自己受了重伤。
I thought her (to be) nice and honest the first time I met her.
我第一次见到她的时候就认为她人很好，很诚实。
含有此类复合宾语的句子变成被动语态时，不定式同样被称之为主语补足语。如：
The young man was considered to have great promise. 这个年轻人被认为大有前途。
The situation was found to be quite encouraging. 形势看来很使人鼓舞。
④以be said, be reported, be known, seem, happen, prove, appear等构成谓语的句子中，动词不定式通常也可看作主语补语。如：
More than 20 people were reported to have been killed in the accident.
据报道，有20多个人死于事故。
I happened to be talking with him when he was hit by a car. 他被汽车撞的时候，我碰巧在和他谈话。
5) 不定式作定语：
不定式在句中作定语通常放在其所修饰的名词或代词之后，以下几种情况常用不定式作定语：
①能带不定式作宾语的动词，其同源名词可以带不定式作定语，常见的有attempt, decision, promise, plan, intention, failure, wish, determination等。如：
He hasn’t kept his promise to write to his parents regularly. 他没有遵守诺言定期给他父母亲写信。
My wish to be a teacher is quite understandable. 我想成为一个教师的愿望是可以理解的。
②常与不定式搭配的形容词，其同源名词一般可以带不定式作定语，常见的有ability, anxiety, eagerness, ambition等。如：
His eagerness to finish his work in time was quite obvious.他急切地想准时完成工作是很明显的。
We admire his ability to speak a foreign language so well.
我们欣赏他能把一门外语说得这么好。
③序数词、形容词最高级或被only, last, next等词修饰的名词可以用不定式作定语。如：
He is always the first person to come and the last one to leave.他总是第一个来最后一个离开。
The next person to attend the meeting is Dr. Baker.下一个出席会议的人是贝克先生。
④还有一些名词经常带不定式作定语。如：person, man, thing, something, anything, nothing, time, way, reason, chance, courage, opportunity等。如：
We students should have the courage to face any difficulty.
我们学生应该有勇气面对任何困难。
He had no reason to leave his friends and live alone on the island.
他没有理由离开他的朋友独自住到岛上去。
⑤不定式作定语时，有时与被修饰的名词之间有意义上的动宾关系，如果该不定式动词是不及物动词，它后面需加上适当的介词。如：
There is nothing to worry about. 没什么可担心的。
There are many interesting books to choose from, but I don’t know which to borrow. 有很多有趣的书可以挑选，但我不知道该借哪一本。
6) 不定式作状语：
不定式作状语可以表示行为的目的、结果、原因、条件等。
① 不定式作目的状语，有时也可以用in order (not) to, so as (not) to结构。如：
In order to protect the young plants from the sun, Mother put them in the shade.
为了保护幼苗不被太阳晒坏，妈妈把它们放到了阴凉处。
He got up very early this morning so as not to be late for school again.
今天早上他起身很早以免上学再迟到。
注意：so as (not) to do不可以置于句首。
②不定式作结果状语，常见的结构有too…to, enough…to, so…as to, such…as to, only to…等。如：
The question is too difficult for me to answer. 对我来说，这个问题很难回答。
He said he was clever enough to deal with it by himself.他说他足够聪明可以独自应付这件事。
Will you be so kind as to turn down the radio? 请你帮我把收音机调低一点好吗？
He woke up only to find himself in hospital. 他醒来发现自己在医院里。
注意：too…to通常表示太……而不……，但在下列句子中没有否定的意思。
She is only too glad to stay at home. 她太想留在家里了。
He is too anxious to know the examination results. 他很急切地想知道考试结果。
③不定式作原因状语，通常用来修饰表示情感、心理状态、性格等的形容词。常见的形容词有：happy, glad, lucky, fortunate, surprised, angry, anxious, ready, quick, slow, cruel, clever, frightened, shocked, sorry, eager, proud, disappointed, foolish, impatient, unwise, naughty等。如：
They are surprised to learn of his death. 得知他死亡的消息，他们很惊讶。
We are proud to be young people of new China. 成为新中国的青年，我们感到很骄傲。
另外，hard, difficult, easy, fit，comfortable等词也可以接动词不定式。这时候，作句子主语的除了是表示人的词外，还可以是表示物的词。如：
The water is not fit to drink. 这水不适合饮用。
The room is very comfortable to live in. 这个房间住起来很舒服。
注意：后两句中的不定式与句子的主语或宾语之间是动宾关系，此时如果不定式动词是不及物动词，则需要带上适当的介词。
