be动词的一般现在时有三种形式

be动词的一般现在时有三种形式，即：am, is, are。

1. 如果主语是第一人称I（我）时，be动词用am。

如：I am a student. 我是一名学生。

I am 还可缩写成I'm。如：

I'm David. 我是大卫。

2. 如果主语是you （你，你们）, they （他们，它们，她们）或名词复数（两个以上的人或物）时，be动词必须用are。

如：Are you twelve? 你是十二岁吗？

Tom and Lily are good friends. 汤姆和莉莉是好朋友。

They are at school. 他们在学校。

are与主语还可缩写。如：We are= We're，They are =They're, You are = You're。而are与not

可缩写成aren't。

如：They aren't students. 他们不是学生。但是am与not不能缩写。

3. 如果主语是单数名词、不可数名词或单数第三人称代词（he, she, it）时，be动词用is。

如:My mother is a teacher. 我的妈妈是一名老师。

He is a student. 他是一名学生。

is也可与主语缩写,如: He is = He's, My mother is = My mother's等。但是This is不可缩写。而is 与not可缩写成isn't。

如:This isn't a book. 这不是一本书。

根据以上叙述我们可以把动词的用法以口诀的形式表述出来：

我（I）是am,

你（you）是are,

剩下is留给她（she）, 他（he）, 它（it）,

两个以上都用are。

英语的be 动词是个用法比较复杂的动词。复杂的原因有两点：

1、除了原形的be 之外，对于不同人称代词以及单数名词和复数名词，be 会有各种变化形式和缩写形式。概括一下有七种形式：be, am, is, are, was, were, been, being。它们与人称代词和名词单、复数的搭配关系是：

现在时I am, you are, he/she/it/ is, we/you/they are；名词单数、不可数名词用is，复数用are。

缩略式I'm, you're, he's, we're, you're, they're

否定缩略式I'm not, isn't, aren't

过去时I was, you were, he/she/it/ was, we/you/they were；名词单数、不可数名词用was，复数用were。否定缩略式wasn't, weren't

过去分词been

现在分词being

2、在句子中，be有两种主要作用：一是作为系动词(The Linking Verb)，本身可以作用谓语动词；二是做为助动词(The Auxiliary Verb)，与谓语动词一起构成各种时态和被动语态等。

下面做个简要的讲解。

一、be 动词做系动词

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：