Period three Grammar

情态动词表示"推测"的用法

英语中，情态动词can / could, may / might, must / can, would / should 等都可以表示"推测"。具体用法如下：

1. can 和could

can 表示推测时，可能性比较大，常用于疑问句或否定句中，不用于肯定句中， 意为"不可能"。表示一种有把握的推测。表示否定时， can't语气最强。 如：

It can't be Mr Li. He has gone to Nanjing already.

They can't know the answer. Let me explain it to them.

That can't be her husband. She is still single.

could 表示推测时，可以用于否定句中，也可以用在后面跟动词原形的肯定句中。表示可能性不大的推测，意思相当于may / might。如：

Anything could happen if you do not obey the rule.

It could be true. But I still doubt it.

2. may和might

may / might 表示一种可能性很小的推测。多用在肯定句或否定句中，might 用在疑问句中表示"可能"，语气最弱。 如：

My English teacher may be correcting our exercises in her office.

My sister may not be in her room at this moment.

The scientists might be discussing the pollution problem.

3. must 和can

在表示推测的情态动词中，must 的把握性最大，意为"一定；肯定"。表示对一般情况的推测。 如：

You sister must be a doctor, isn't she?

The boys must be playing football on the playground, aren't they?

Li Ping must be punished by his father.

（以上几句要注意反意疑问句的构成）

can的推测用法：肯定句中，can 可以表示客观的（理论的）可能性，并不涉