剑桥MSE基础语法丨情态动词(一)

情态动词的作用:
Probability可能性
Ability能力
Permission准许
Requests, offers and invitations请求,提议,邀请
Suggestions and obligations建议和义务
1.Probability可能性
情态动词可用来表达可能性,我们将可能性分为三个程度:不可能,可能,一定。
可能
我们使用may/might/could表达可能,但不确定:
They may come by car. (= Maybe they will come by car.)
They might be at home. (= Maybe they are at home.)
我们使用can来概括表达可能的事:
It can be very cold here in winter. (= It is sometimes very cold here in winter.)
You can easily get lost in this town. (= People often get lost in this town.)
那么,同样是表达可能,can和may/might/could有什么区别呢?
感受一下这两个例句就会知道啦:
That dog can be dangerous.(= 这只狗有时候会很凶,讲话者很确定这一点。)
That dog may/might/could be dangerous.(= 这只狗可能会很凶,讲话者不确定这一点。)
注意!我们不使用can来谈论具体的事件。
A: Where's John?
B: I'm not sure. He may/might/could be (NOT can) in his office.
不可能
我们使用can't/cannot表达绝不可能:
That can't be true.
那不可能是真的。
You cannot be serious.
你不是认真的吧。
一定
我们使用must表示非常确信的事,并且,一般会有理由支撑:
It's getting dark. It must be quite late.
天黑了。一定很晚了。
You haven't eaten all day. You must be hungry.
你一整天没吃东西了。你一定饿了。
我们使用should来表示某些事是真的,并且有理由这么认为:
Ask Miranda. She should know.
去问米兰达。她应该知道。
It's nearly six o'clock. They should arrive soon.
快六点了。他们应该很快到达。
must更为强硬+确定。
2:Ability能力
我们使用can/can't表达有无某项技能、能力:
She can speak several languages.
她会说几种语言。
They can't dance very well.
他们不太会跳舞。
或在现在或将来能否做到某事:
I can see you.
我能看见你。
Help! I can't breathe.
救命啊!我无法呼吸。
如果要表达过去能够做到某事,则使用could:
She could speak several languages.
她会说几种语言。
I couldn't see you.
我看不见你。
3:Permission准许
Asking for permission
我们使用can/could/may来请求允许:
Can I ask a question, please?
我能问个问题吗?
Could I ask a question, please?
请问我可以问一个问题吗?
May I ask a question, please?
请问我可以问一个问题吗?
could/may更加正式、有礼貌。
Giving permission
我们使用can/may来给予准许:
You can go home now.
你现在可以回家了。
You may go home now.
你现在可以回家了。
同样,may更加正式、有礼貌。
我们还使用can表达某人得到了允许去做某事:
Students can go outside after lunch.
学生可以在午饭后出去。
Refusing permission
我们使用can't和may not来拒绝请求:
You can't go home now.
你现在不能回家。
Students may not go outside after lunch.
学生午饭后不可以出去。

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