be动词与情态动词的区别？？？

情态动词 (Model Verbs) 又称为情态助动词 (Model Auxil-iaries)。英语中助动词主要有两类：一是基本助动词，如have, do, be；二是情态助动词，如may, must, need等。情态动词与其他动词连用表示说话人的语气。情态动词可表达建议、要求、可能和意愿等。情态动词没有人称和数的变化。在大学英语四、六级考试中，情态动词部分重点测试以下内容：

（1）情态动词+行为动词完成式

（2）情态动词+行为动词进行式

（3）情态动词+行为动词完成进行式

（4）某些情态动词的特殊用法

一、情态动词+行为动词完成式

情态动词+行为动词完成式即“情态动词+ have + v-ed分词”，表示对过去行为或动作进行推测、评论或判断。

1. must have v-ed

must have v-ed 表示推测过去某事“一定”发生了。其否定形式为：can’t / couldn’t have v-ed, 表示过去不可能发生某事。例如：

1）Since the ditch is full of water, it must have rained last night.

2）You couldn’t have met my grandmother. She died before you were born.

2. could have v-ed

could have v-ed 表示推测过去某动作“很可能”发生了。例如：

1）“The dictionary has disappeared. Who could have taken it?”

2）“Tom could have taken it. He was alone yesterday.”

3.may / might have v-ed

may / might have v-ed 表示推测过去某事“也许”发生了.may 比 might 表示的可能性在说话人看来稍大些。例如：

I can’t find my keys. I may / might have left them at the school yesterday.

4. ought to / should have v-ed 和 ought not to / shouldn’t have v-ed

ought to / should have v-ed 和 ought not to / shouldn’t have v-ed 用于对已发生的情况表示“责备”、“不满”，分别表示“本应该…”和“本不应该…”。例如：

1）With all the work finished, I should have gone to the party last night.

2）You ought not to make fun of him. He is not the one you laugh at but learn from.

5. needn’t have v-ed

needn’t have v-ed 表示过去做了某事，但没有做的必要， 意为“本没必要…”。例如：

You needn’t have waken me up; I don’t have to go to work today.

注：表示推测过去某动作发生的可能性时，就表示的可能性程度而言，must最大，could其次，may更次之，might最小。例如：

“I wonder how Tom knew about your past.”

“He must / could / may / might have heard of it from Mary.”

二、情态动词+行为动词进行式

情态动词+行为动词进行式（即情态动词+ be + v-ing形式），表示推测或评论某动作现在是否正在进行。例如：

1）He must be playing basketball in the room.

2）She may be staying at home.

三、情态动词+行为动词完成进行式

情态动词+行为动词完成进行式（即情态动词+ have been + v-ing 形式），表示推测或评论过去某动作是否正在进行或一直在进行。例如：

1）They should have been meeting to discuss the problem.

2）He may / might have been buying stamps in the post office when you saw him.

四、某些情态动词的特殊用法

1. need

考试中主要测试 need 作情态动词与作实义动词的区别，对此，可参见表1.need 作情态动词时，后面跟不带to 的动词不定式，即 “need to”。通常用在疑问句和否定句中，表示询问是否有“必要”，其否定形式为needn’t，表示“不必”；疑问形式为 Need … do? 极少用于肯定句。例如：

1）I don’t think we need turn the light on at that time.

2）Need you ride a bike to school?

情态动词need与实义动词need 在时态、肯定、否定结构上的对比见表1。

2. dare

考试中主要测试dare作情态动词和作实义动词的区别。

情态动词dare 与实义动词dare 在时态、肯定、否定、疑问结构上的对比见表2。

3. can 和 may

考试中主要测试can，may或could，might表示可能性的区别及对may构成的疑问句的回答。

时态 情态动词need 实义动词 need

现 You need (not) do You (don’t) need to do

在

时 He need (not) do He needs (doesn’t need) to do

过 You needed (didn’t need) to do

去

时 He needed (didn’t need) to do

将 You need (not) do You will (not) need to do

来

时 He need (not) do He will (not) need to do

be动词后面 加 形容词 或是 be done 表示被动语态
情态动词 后面加 动词原形 象是：can do, must do,should do.