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being2、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 evening2、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.二、be 动词做助动词助动词be 有两个基本用法，一是与谓语动词一起构成各种时态，二是构成被动语态。
1、“be + 现在分词组”成各种进行式时态。
例如：Tony's maid is washing his new car.The children are playing in the field.Samuel was eating when I came in.We have been living here since 1959.This time next day they will be sitting in the cinema.2、“be + 过去分词”组成被动语态。
例如：Her money in the drawer was stolen.A number of good jobs are taken up byforeigners.David studied in Taiwan but has been trained as a language lecturer in America.The disobedient boy was told to stand out- side the classroom.Steps are being taken to reduce traffic con- gestion during peak hours.Dishonest students will be immediately dealt with.3、being 的分词短语being 也是be 的变化形式之一，它是be 动词的现在分词。
being 一般不单独使用，而是构成“系+表”结构的分词短语，或者构成被动语态的短语。
一般情况下，可以把being短语作为一个词组来整体看待，它在句子中可以作为各种成份，比如主语、表语、定语、状语等。
从大的方面说，being短语属于另外一个语法项目，即：现在分词(短语)的用法。
关于分词(短语)的用法，请参看本站有关文章。
这里，结合全句做一点简单的提示。
例如：Your brother is being very annoying this evening. (表语)Being lost can be a terrifying experience. (主语)He can't stand being kept waiting. (宾语)Did you see that boy being questioned by the police? (定语)Being given a chance, she immediately jumped at it. (状语)The question being settled, we went home. (构成独立主格结构)三、注意事项英语句子中，为了表达时态或被动语态的需要，常常会出现几个助动词连在一块儿使用。
也就是说，助动词be会和其它助动词一起使用。
这时候，整个句子的一般疑问句和否定句，就不一定是对be 进行变化了，而是以第一个助动词为主进行变化。
即哪个助动词在先，就以它为主进行变化。
例如：[肯定句] All the wonderful birds can be found in our Bird Park. (助动词有两个：can be )[疑问句] Can all the wonderful birds be found in our Bird Park? (移第一个can)[否定句] All the wonderful birds can not be found in our Bird Park. (在第一个can 后加not)[肯定句] I have been there before. (两个助动词：have, been )[疑问句] Have you been there before?[否定句] I have not been there before.[肯定句] I shall be having my supper at six tomorrow evening. (两个助动词：shall, be )[疑问句] Will you be having my supper at six tomorrow evening?[否定句] I shall not be having my supper at six tomorrow evening.四、巩固练习从下列各题后所给的四个选项中选择最佳答案填空。