英語入門必備語法知識
單詞的積累和語法的掌握是學習英語的重中之重，下面是小編給大家分享的常用英語語法知識，大家可以作爲學習的參考。
1、系動詞+表語”的結構
當be 動詞做系動詞使用時，主要構成“系動詞+表語”的結構，在句子中做謂語。表語可以是名詞、形容詞、副詞、介詞短語等。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 動詞的一般疑問句，方法是把be 移到主語前面，也可說成是移到句首。
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 動詞用在特殊疑問句
在特殊疑問句裏，be 動詞仍然移到主語前面，但特殊疑問句是以特殊疑問詞開頭的，所以be 動詞只能說是移到主語前面，或者說是在特殊疑問詞的後面。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 動詞的否定句
be 動詞做謂語時，它的否定形式是在be 後加not，並且可以縮寫。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 動詞的祈使句
be 動詞的祈使句有肯定和否定兩種形式。肯定形式是以be 動詞開頭，而否定形式或強調句形，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.
英語中be動詞的用法：
作爲系動詞(也叫連繫動詞，link verb)的be，是英語學習者接觸最早的用法，而且其用法也很多。其基本含義爲“是”，基本用法結構爲“主語+be+表語”，也就是我們常說的主系表結構，其中的表語一般都由名詞、形容詞、數詞或表地點、時間等的短語來充當。
系動詞be有各種時態的變化，也會和情態動詞連用。
(一)be的時態變化
系動詞be會有一般現在時、一般過去時、一般將來時、現在完成時、過去完成時等的時態變化。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與情態動詞的連用
其用法爲：情態動詞+系動詞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動詞的一般現在時用法：
be動詞是系動詞的一種，表示“……是……”的意思。現在式(The Present Forms)有am，is，are三種。這三種動詞的原形是be，所以它們稱爲be動詞。
be動詞句型的構成
肯定句：主語 + be動詞(am/is/are)...
否定句：主語 + be動詞(am/is/are) + not...
疑問句：be動詞(am/is/are) + 主語...?
疑問代詞/疑問副詞 + be動詞(am/is/are) + 主語...?
be動詞的肯定句
句型：主語 + be動詞...
be動詞的肯定句由“主語 + be動詞(am/is/are) + 表語”構成：
I am a doctor.我是一名醫生。
Mary is at work.瑪麗在工作。
He is very brilliant.他非常聰明。
It is a nice day.今天天氣晴朗。
You are my only friend.你是我惟一的朋友。
They are students.他們是學生。
be動詞的否定句
句型：主語 + be動詞(am/is/are) + not...
be動詞一般現在時的否定句結構，是在be動詞am，is，are之後加not：
We aren't her classmates.我們不是她的同班同學。
I'm not Tom.我不是湯姆。(I'm是I am的縮寫，讀作/aim/。)
It's not a cat，but a dog.這不是貓，而是狗。
Things are not always what they seem(to be).事物並不總是與表象一致。
be動詞否定句的縮寫方式：
is not的縮寫是isn't，讀作/′iznt/;are not的縮寫是aren't，讀作/a：nt/;I am～的否定句是I am not～，縮寫爲I'm not～;am not不縮寫在一起。
be動詞的過去時用法：
be動詞過去時的構成
肯定句：主語 + be動詞的過去式(was/were)...
否定句：主語 + be動詞的過去式(was/were) + not...
疑問句：be動詞的過去式(Was/Were) + 主語...?
疑問代詞/疑問副詞 + was/were + 主詞...?
be動詞過去時的肯定句
句型：主語 + was/were...
be動詞過去時由“主語 + be動詞的過去式(was/were) + 表語”構成：
I was here yesterday.昨天我在這裏。
We were hungry.我們當時餓了。
The concert was last night.音樂會在昨晚舉行。
The biggest problem was that we didn't have enough time.最大的問題是我們當時沒有足夠的時間。
There were some students on the campus.校園裏有一些學生。
be動詞過去時的否定句
句型：主語 + was/were + not...
be動詞過去時的否定句結構是在be動詞過去式was/were後面加上not。否定式的was not，were not大多使用縮寫形式wasn't(讀作/′w znt/)和weren't(讀作/w nt/)：
I was not here yesterday.昨天我不在這裏。
He wasn't busy the other day.前幾天他不忙。
There weren't any students in the classroom.教室裏一個學生也沒有。
