英语入门必备语法知识
单词的积累和语法的掌握是学习英语的重中之重，下面是小编给大家分享的常用英语语法知识，大家可以作为学习的参考。
1、系动词+表语”的结构
当be 动词做系动词使用时，主要构成“系动词+表语”的结构，在句子中做谓语。表语可以是名词、形容词、副词、介词短语等。例如：
The man is a science teacher.
Mary's new dresses are colourful.
Mother is in the kitchen now.
I have been there before.
They shall be here at 10:00 tommorow.
That can't be true.
You are not being very polite.
Your brother is being very annoying this evening
2、be 动词的一般疑问句，方法是把be 移到主语前面，也可说成是移到句首。
Is the man a science teacher? Yes, he is. / No, he isn't.
Are Mary's new dresses colourful? Yes, they are. / No, they aren't.
Was mother in the kitchen then? Yes, she was. / No, she wasn't.
Were you at home the day before yesterday? Yes, I was. / No, I wasn't.
Was she late this morning? Yes, she was. / No, she wasn't.
3、be 动词用在特殊疑问句
在特殊疑问句里，be 动词仍然移到主语前面，但特殊疑问句是以特殊疑问词开头的，所以be 动词只能说是移到主语前面，或者说是在特殊疑问词的后面。例如：
Whose bike is broken? Xiao Ming's bike is.
Who was singing in the room? Mr. Zhang was.
Where are you from? I am from Wuhu.
What class were you in? We were in Class 2.
How old is Tom? He is ten.
4、be 动词的否定句
be 动词做谓语时，它的否定形式是在be 后加not，并且可以缩写。例如：
It is not sunny today.
Tom and his friends are not in the park.
You were not nine years old when I went to the university.
He was not often late for his class when he was a student.
I wasn't here yesterday.
My parents weren't at home last Sunday.
5、be 动词的祈使句
be 动词的祈使句有肯定和否定两种形式。肯定形式是以be 动词开头，而否定形式或强调句形，要加don't 或do。例如：
Be careful!
Be a good boy!
Don't be silly!
Don't be a fool!
Do be obedient!
Do be careful.
英语中be动词的用法：
作为系动词(也叫连系动词，link verb)的be，是英语学习者接触最早的用法，而且其用法也很多。其基本含义为“是”，基本用法结构为“主语+be+表语”，也就是我们常说的主系表结构，其中的表语一般都由名词、形容词、数词或表地点、时间等的短语来充当。
系动词be有各种时态的变化，也会和情态动词连用。
(一)be的时态变化
系动词be会有一般现在时、一般过去时、一般将来时、现在完成时、过去完成时等的时态变化。如：
He isa student.
They werein the park yesterday.
It will be cloudy tomorrow.
He has been ill for six days.
It had been three hours before she left the hat shop.
(二)be与情态动词的连用
其用法为：情态动词+系动词be原形。如：
It must be Lucy's book. Her name is on the cover.
It can be very difficult for us to memorize too many words within such a short time.
She should be here on time tomorrow.
be动词的一般现在时用法：
be动词是系动词的一种，表示“……是……”的意思。现在式(The Present Forms)有am，is，are三种。这三种动词的原形是be，所以它们称为be动词。
be动词句型的构成
肯定句：主语 + be动词(am/is/are)...
否定句：主语 + be动词(am/is/are) + not...
疑问句：be动词(am/is/are) + 主语...?
疑问代词/疑问副词 + be动词(am/is/are) + 主语...?
be动词的肯定句
句型：主语 + be动词...
be动词的肯定句由“主语 + be动词(am/is/are) + 表语”构成：
I am a doctor.我是一名医生。
Mary is at work.玛丽在工作。
He is very brilliant.他非常聪明。
It is a nice day.今天天气晴朗。
You are my only friend.你是我惟一的朋友。
They are students.他们是学生。
be动词的否定句
句型：主语 + be动词(am/is/are) + not...
be动词一般现在时的否定句结构，是在be动词am，is，are之后加not：
We aren't her classmates.我们不是她的同班同学。
I'm not Tom.我不是汤姆。(I'm是I am的缩写，读作/aim/。)
It's not a cat，but a dog.这不是猫，而是狗。
Things are not always what they seem(to be).事物并不总是与表象一致。
be动词否定句的缩写方式：
is not的缩写是isn't，读作/′iznt/;are not的缩写是aren't，读作/a：nt/;I am～的否定句是I am not～，缩写为I'm not～;am not不缩写在一起。
be动词的过去时用法：
be动词过去时的构成
肯定句：主语 + be动词的过去式(was/were)...
否定句：主语 + be动词的过去式(was/were) + not...
疑问句：be动词的过去式(Was/Were) + 主语...?
疑问代词/疑问副词 + was/were + 主词...?
be动词过去时的肯定句
句型：主语 + was/were...
be动词过去时由“主语 + be动词的过去式(was/were) + 表语”构成：
I was here yesterday.昨天我在这里。
We were hungry.我们当时饿了。
The concert was last night.音乐会在昨晚举行。
The biggest problem was that we didn't have enough time.最大的问题是我们当时没有足够的时间。
There were some students on the campus.校园里有一些学生。
be动词过去时的否定句
句型：主语 + was/were + not...
be动词过去时的否定句结构是在be动词过去式was/were后面加上not。否定式的was not，were not大多使用缩写形式wasn't(读作/′w znt/)和weren't(读作/w nt/)：
I was not here yesterday.昨天我不在这里。
He wasn't busy the other day.前几天他不忙。
There weren't any students in the classroom.教室里一个学生也没有。
