从句是相对于主句而言的，即它是从属于某一个主句，而不能单独作一个句子。在英语中，主要有三大从句，即名词性从句（包括主语从句，宾语从句，表语从句，同位语从句）、形容词性从句（即定语从句）、副词性从句（即状语从句，包括时间、条件、结果、目的、原因、让步、地点、方式等）。
主语从句用作主语，如：：
That the earth is round is true. 地球为圆的是真实的。
宾语从句用作宾语。如：
Do you know where he lives?
表语从句用作表语，如：
My opinion is that you should not go alone. 我的意见是你不应单独前往。
同位语从句用于解释说明前面的名词。如：
The fact that the earth is round is true. 地球是圆的的事实是真实的。（that从句用于解释说明the fact）
定语从句相当于一个形容词，用于修饰前面的名词。如：
The student who answered the question was John. 回答问题的学生是John.
状语从句相当于一个副词，如：
When it rains, I usually go to school by bus. 天下雨时，我通常坐公共汽车上学。（时间状语）
If he comes tomorrow, you will see him. 如果他明天来，你就可以看见他。（if 引导的条件状语从句，其结构为：if +状语从句，＋主句）。要注意在状语从句中有一个规则是“主将从现”，即主句是将来时，则从句要用一般现在时表示将来。
主句和从句的划分方法是相同的。句子的成分从谓语动词处来划分比较容易。谓语动词前面的部分是主语，后面常接宾语，修饰谓语动词的是状语，修饰主语、宾语的是定语，若谓语是系动词，则系动词后的部分是表语。如：
I am a teacher. 其中，I 是主语，am是谓语，a teacher 是表语。
He likes playing football very mucy. 其中，he是主语，likes是谓语，playing football是宾语，very much是状语。
回答者：f77917 - 同进士出身 六级 12-7 20:18
从句：从句是指用于复合句中担当某个句子成分的主谓结构。虽说从句自身的句子结构是完整的, 但是它不能视为独立，它离开主语就无法独立完整的表达意思
从句
一 名词性从句:
1. 主要包括主语从句，宾语从句，表语从句和同位语从句. 一般由that 引起，也可由who, what, when, why, which, whom, whether, how 引起.
What you need is more practice.
The question is whether it is worth doing.
We must find out who did all this.
We expressed the hope that he would come to China again.
2. 主语从句很多情况下都可以放到句子后面，而用代词it作形式上的主语. 例如:
It isn’t likely that I should accept such an offer as that.
It is still a question when we shall have our sports meet.
3. 形式宾语
I think it best that you should stay here.
She took it for
granted that he would receive it with shame.
4. 由名词性关系代词whatever, whoever, whichever 等引起的宾语从句
He will do whatever the teacher asks him to do.
I’ll take whoever wants to go with me to the theatre.
Take whichever you like best.
5. whether and if 都能引导从句, 但用法有所不同. 当主语从句直接位于句首时，应用whether，而不用if. Whether 后能直接or not, 但if 不能.
Whether he will come or not is not known.
6. 在名词reason后的表语从句必须用that引导, 不可误用 because.
The reason why he is often late for class is that he has the bad habit of getting up late in the morning.
二: 定语从句
1. 引导定语从句的关系词有who, whom, whose, that, when, where, why and which. 在非限制定语从句中, 只可用which, who, whose, where , when., 如果指代前面整个句子, 多用which.
The dog that/which was lost has been found.
Those who are in favor of the proposal are expected to discuss it in detail after the meeting.
There are many organizations whose purpose is to help the homeless.
The days when we had to rely on wool, cotton or silk for our clothes have now passed.
Air moves from places where the pressure was high to places where the pressure is low.
This is the reason why he refused to help us.
He was born in 1976, when an earthquake struck the country.
They turned a blind eye to the suffering of the people, which enraged all of us.
2. 当引导定语从句的先行词前有all, any, no, little, much, very first 等词, 或先行词前为形容词最高级所修饰时，或先行词为all, anything, nothing, something, everything 时，从句的引导词只能用that.
The only thing that matters to the children is how soon they can have their holiday.
These are the very points that puzzle me.
Is there anything that bothers you?
This is the best film that was ever produced by the company.
3. as 可做引导词引导定语从句, 多和such, the same 连用. As 引导的定语从句也可修饰整个句子, 既可放在先行词后，也可放在句子开头.
Such people as you describe are rare nowadays.
The boy was run over by a motor-car, as often happened in pre-liberation Shanghai.
As is often the case, the girl forgot to bring her dictionary.
We are opposed to such ideas as are not based upon objective facts.
4. 介词+which/whom/whose从句
The driver is the man from whose room she had stolen the gold watch.
Language is a tool by means of which people communicate ideas with each other.
Jane spent all evening talking about her latest book, of which none of us had ever heard.
Water dissolves a part of nearly everything _______ it comes in contact.
a. where b. that c with which d as soon as
5. 代/名+介词+which 从句
he is needing a book, the name of which I don't know.
In factories and in our daily life, there are many waste materials, all of which can he turned into useful things un
der certain condition.
To make an objective test the teacher writes a series of questions, each of which has only one correct answer.
6. 同位语从句和定语从句
The news that he has been admitted by Harvard University is very pleasing.
The news the you told me was really exciting.
7. 难句:
He is one of the men who were chosen to represent the group.
He is the only one of those boys who is willing to take on another assignment.
I shall never forget the day when we first met.
I remember the morning when he first came to school.
I shall never forget the days which I spent in the countryside.
The room where he lived is kept in good repair.
Alva found a place in the cellar ______ he uses as his first laboratory.
A where B which C what D in which
The way in which/that you answered the questions was admirable.
三 状语从句: 修饰主句中的动词, 形容词和副词, 通常有从属连词引导, 按其意义和作用可分为时间, 地点, 条件, 原因, 让步, 目的, 结果, 方式, 比较.等
1. 时间状语从句:
1) 常见连词有 after, as, before, once, since, till, (not)until, when, whenever(no matter when), while, as long as, as soon as etc.
As you look at yourself in a mirror, you’ll seen an identical image of yourself.
It is a long time before it is possible to test the medicine on human patients.
It was not until…that
Not until…did he…
Not until I received the letter, did I know he had gone to America.
It was not until….
When I got to the airport, I suddenly remembered that I had left the ticket behind.
I was about to leave, when something occurred which attracted my attention.
Whenever we have difficulty, he’ll come to help us.
2) no sooner…than, hardly(scarcely, barely)…when: 刚做…就….
No sooner had I opened the door than the telephone rang.
She had scarcely news when she fainted.
3) 还有 immediately, directly, instantly, the moment, the minute, the instant, the second, every time etc
I’ll tell you about it the moment you come.
I got in touch with him immediately I received his letter.
2. 地点状语从句: 一般用where or wherever 引导
I will stand where I can see the parade clearly.
Wherever they went, they were warmly welcome.
3. 条件状语从句：真实条件从句:if, unless, so long as, provided that, supposing that, on condition that, in the event that, in case that etc
I will not go to her party if she doesn’t invite me.
I will not go to her party unless she invites me.
4. 原因状语从句: 从属连词有because, as ,since, for, now, that, in that, seeing that, considering that(
鉴于，由于)
As the school regulations are written quite clearly, there is nothing more to be explained. whether是什么意思
Considering that the sweater was hard made, it was not expensive.
Seeing that they are inexperienced, they are doing quite a good job.
5. 让步状语从句:
1): even if, though, even though, while(尽管) no
matter what/how/which, however, whatever, whichever, however etc.
He will not give up smoking even though the doctor advises him to.
Whatever the consequence may be, I will be on your side.
However hard she tried to explain, nobody trusted her.
It has been the same result, whichever way you do it.
2) 由as 引起的让步从句, 语气较强烈，被强调的词须放在句首.
Simple as the question may seem, it is not at all common in nature.
Cold as it is, the children play outdoors.
Much as I respect him, I can’t agree with him.
Object as you may, I will go on with my plan.
3) whether…or，不管…或…
whether you be a student or a teacher, you are required to obey the regulations of the school.
6. 结果状语从句: so that, so…that, such…that
He is so humorous that we’ll never forget him.
She is such a nice girl that everybody likes to make friends with her.
7. 目的状语从句: so that, in order that, for fear that, lest, in case
I checked all the results time and again for fear that there should be any mistakes.
Telephone us in advance in order that we might make the necessary arragements.
8. 方式状语从句: as, just as, as if: 如同…一样
we should do the exercise as our teacher tells us.
You talk as if you had really been there.
It looks as if it is going to rain.
Nails protect the ends of human fingers and toes as claw protect the toes of most animals.
The young man operates the machine as the old worker has taught him.
9. 比较状语从句:
1) as…as, not so/as…as
the film was not so exciting as we expected.
The history of nursing is as old as the history of man.
She likes them almost as much as Paul does.
2) 比较级+than, so much/a lot more than
She looks much younger than she is.
The universe is a lot more complicated than you think.
3) no more…than, not more…than, less…than
Jack is no more frightened than Mike is.
Jack is not more frightened than Mike is. 不像马克那么害怕
Tom is no more rich than Black
3) the more…the more
The farther north you go, the severer the winter is.
The more I see of him, the less I like him.