有人敲门。你没有等任何人,除了你的姐姐。
- That must be my sister. —— 几乎可以肯定。
- That might be my sister. —— 有可能。
- That can't be my sister — she's in Rome. —— 绝无可能。
同一个情境,三种不同程度的确定性,变化的只是情态动词。这里说的不是许可,也不是能力,而是你有多确定。
确定程度的等级表
| 情态动词 | 确定程度 | 例句 |
|---|---|---|
| must | 约 95%——没有别的解释 | You must be tired. |
| may / might / could | 约 40%——众多可能性之一 | She might be at work. |
| can't | 约 0%——不可能 | It can't be true. |
May、might 和 could 在表达推测时意思非常接近,可以视为可以互换。在口语中最常用的是 might。
两端并不是彼此的镜像
这里是最主要的陷阱。must be 的反义词不是 mustn't be。
- He must be at home.(确信他在家。)
- He can't be at home.(确信他不在家。)
Mustn't 这个形式确实存在,但表示的是禁止——you mustn't smoke here——绝不会表示「确信不是这样」。用 mustn't 来否定推测,是 B1 水平学习者中最顽固的错误之一。
否定 might be 则简单得多:might not be。She might not be home yet.
对过去的推测
加上 have + 过去分词。情态动词本身不需要变化。
| 关于现在 | 关于过去 |
|---|---|
| must be | must have been |
| might be | might have been |
| can't be | can't have been |
- The ground is wet. It must have rained.
- I don't know where she is — she might have missed the train.
- You can't have seen him yesterday; he was in hospital.
在口语中,have 几乎被弱化到听不见:must've、might've、can't've。听起来很像「must of」——这也是这种常见拼写错误的来源,而这种写法永远都是错的。
永远不要写「must of」「might of」或「could of」。 它们只是缩读被听错的产物。这个词永远是 have。
对正在发生的事情的推测
用 be + -ing:
- She's not answering. She must be driving.
- He might be working late.
- They can't be sleeping — the lights are on.
对过去也是同样的道理:He must have been sleeping.
对话中的用法
汤姆在哪儿?
A: Tom's not answering his phone.
B: He must be on the train — there's no signal in the tunnel.
A: He can't be. He said he was leaving at six.
B: Then he might have missed it. Or he could have forgotten to charge his phone.
四种不同强度的推测,却没有一个用到 maybe 或 probably 这样的词。全部的表达工作都由情态动词完成。
自我检测
下面的测验重点考察 can't 与 mustn't 的区别,以及过去式的构成方式。