二者時態(tài)不同，is是一般現(xiàn)在時態(tài)，was是過去時態(tài)。二者用法不同，“現(xiàn)在時間”用is，“過去時間”用was。be動詞的形式有am，is，are，been，being，was，were。

be動詞

be（be/is/are/am/was/were)[bi:]vi

he is, we are, you are, they are （縮略式 I'm, you're, he's, we're, you're, they're）, （否定縮略式 I'm not, isn't, aren't）, 過去時 I was, you were, he was, we were, you were, they were （過去時否定縮略式 wasn't, weren't）,過去分詞been,現(xiàn)在分詞being

“Be”除了原形的“be”之外，還有另外七種形式：am, is, are, been, being, was, were.

在句子中，“be”可以是主動詞(The Principal Verb)或助動詞(The Auxiliary Verb)

例句對照

當(dāng)做主動詞時，“be”在性質(zhì)上屬于接系動詞(The Linking Verb), 后面要有名詞、形容詞、地方副詞或短語作補足語(The Complement)。例如：

The man is a science teacher.

這個男子是一位科學(xué)教師。

Mary's new dresses are colourful.

瑪麗的新衣服色彩鮮艷。

I have been there before.

我以前去過那里。

My mother is in the kitchen now.

我媽媽現(xiàn)在在廚房里。

這四個都是陳述句，可以變成疑問句，方法簡單，把主語和“be”或助動詞對換位置即可：

Is the man a science teacher?

Are Mary's new dresses colourful?

Have I been there before?

Is mother in the kitchen now?