英语中be动词的三种基本形式为：am，is，are。以下是be动词的详细说明及用法，希望对大家有所帮助。

在英语中，be动词包括：am、is、are、was、were、being。它们分别用于不同的人称和数。

1、am，is和are用于不同的人称和数。am用于第一人称单数，如：I am a teacher.我是一名老师。is用于第三人称单数，如：He is Tom’s father. It is a book. are用于第二人称单、复数和第一、三人称的复数，如：You are a student. We are students, too.

2、am，is和are可用于构成否定句和疑问句。如：I'm not from China. → Are you from China? (对I am的提问比较特别)

He’s thirteen years old. → He isn’t thirteen years old. → Is he thirteen years old? They are policemen. → They aren’t policemen. → Are they policemen?

在使用am，is，are时，注意它们的缩写形式。另外，am，is，are与this，these，those在一起时一般不缩写。

3、be还可以位于句首，表示向别人提出要求，如：Be a good student! 做个好学生！

系动词be的用法十分广泛。它作为系动词时的基本含义为“是”，常用于主系表结构中，表语通常由名词、形容词、数词或描述地点、时间的短语等构成。be有各种时态变化，也可与情态动词连用。

（一）be的时态变化。be有各种时态的变化，如：He is a student. They were in 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。例如：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作为助动词时，用于构成进行时态和被动语态。在进行时态中，be与主要动词的现在分词结合，构成各种时态，如：He is reading in the library now. She was swimming in the river this time yesterday. They will be arriving in Beijing tomorrow. We have been learning English for ten years.

在被动语态中，be与主要动词的过去分词结合，构成被动语态，如：Chinese is widely used around the world nowadays. The window was broken by the naughty boy just now. Your watch has already been repaired.

be在特殊句型中也有特别用法。例如，be going to do表示“打算或将要”；be about to do表示“刚要，即将”；be to do表示“按计划要做”。

There be句型使用be与there一起，表示存在。如：There is a white ruler on the desk. There were a great many people in the car race last year.

祈使句中的be以Be开头或Don't be开头，表示命令或建议等，如：Be patient! Don't be so hard on me!

在虚拟语气中，be有时放在句首，引出虚拟语气，如：Be he rich or poor, she will marry him. Be it true or not, she will see it herself. 这些句子相当于：Whether he be rich or poor, she will marry him. Whether it be true or not, she will see it herself.