Model Verbs: 情态动词
一. 表示许可:有may, might, can, could。其中might. could则语气较委婉,但回答由他们引起的问句时,则不用might, could而用can。 1)May \ Might \ Can \ Could I keep the book for a few days? Yes, you can. 否定形式可用may not, can not或must not,不用might not。 2)Visitors may not (或can not/mustn’t) touch the button.
二、表示能力:can; be able to. be able to用于各种时态。在一般过去时中,若指“能够并且通过某种努力完成某桩事”,我们必须用be able to。
- Cats can\ are able to climb trees very quickly.
- A big fire broke out last night, but everyone was able to escape from the house.
三、表示“责任和义务”的情态动词有must(主观),have to(客观), mustn’t 表示“不可以、不允许”,而have to否定形式:not have to/ needn’t。
- As there was no bus, we had to walk back home. (客观条件)
- You mustn’t shout like that to your parents. (不可以、不允许)
- You don’t have to\ needn’t work if you don’t feel well.
四、用于推测:must, may, might, can, could . 但疑问句中只能用can, could.
- He looks pale. He__________ be ill.
- —Who _____it be? It _____(not) be Mr. Smith, for he has just left for Paris. —It ________be Mr. Brown, for he has something to discuss with me.
- He said he didn’t feel very well. He _____(not) come to the meeting this evening.
(1.must 2. can, can’t, must 3. may\might not)
▲注意: 表推测时 must, should (ought to) , may, could , might 可能性依次递减。should, ought to “应该…”较多地用于预测将来的事。can表示理论上的可能性,用于泛指.may, could, might表示事实上的可能性,用于特指具体的,可能将要发生的事。
- He should be back by now. 他现在该回来了。
- The teacher has explained it several times. There ought to be no problem for them.
- A dog can be dangerous to you 狗可能给人带来危险。(有这种可能性) / This dog is very clever. It may (或might/could) help you find your key. 这条狗非常聪明,他可能会帮助你找到钥匙。指具体的事有可能发生。
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