情态动词的时态用法

江苏 田 智

《学英语》高三版，1994/Nov.20.

英语情态动词中，除了ought to、must和need没有其相应的过去式、used to没有其相应的现在式(只用于过去时)外，其它都有其现在式和其相应的过去式两种形式。情态动词的时态用法比较复杂，近几年的高考多次考到情态动词的用法，现试将其一般用法归纳如下

一、情态动词的现在式可用于：

1．现在或将来时态。如：

You can start work tomorrow．

We must leave early tomorrow morning．

I  think he may stay here now．

2、主句谓语动词为过去时的间接引语中。如：

He said the children must／ought  to／needn't／daren’t go out and play．

但在其它情况下，过去时要用其相应的过去式。如：

Yesterday，the children had to／ dared not go out and play．

二、情态动词的过去式较为复杂，下列情况下可用于现在时或将来时，如：

1、口语中表示说话人的客气或强调个人倾向，也可以表示考虑问题的周密性，如：

Could you wait a few days for the money?

(比较：Can you wait a few days for the money？）

Would you be good enough to come and see me as soon as you can?

(比较：Will you be good enough to come and see me as soon as you can?)

再看NMET(92)中一道选择填空题：

---Would you do me a favour?

---Yes ,I will.

问话中“Would"表示说话人在委婉提出要求，答句中“will"表示答话人语气肯定的答复。

2、“should ／ could／would／might+完成式”表示说话人事后对已经发生的事情的责备、埋怨，或进行相反的推测。如：

The plant is dead. I should have given it more water．(MET 87A)

这棵树死了。我本该多给它浇些水.

He  might have given you more help even though he was very  busy．

(MET(9 0A)

尽管他当时很忙，但本来还是可以给你更多的帮助。

一We could have walked to the station，it was so near．

一Yes．A taxi wasn't at all necessary.（MET(92)）

一我们本可以步行去车站。它那么近。

一是的。当时乘出租车完全不必要。

3．用于条件虚拟语气的主句谓语中。如：

If he had taken my advice, he would be better now.

lf there were no accident on the way ,they might arrive here tomorrow morning·

4．ought to／should表示“应该"、should表示“竟然”时：

You ought to／should tell the truth before your teacher·.

Why should you treat him like that?

你怎么竟这样时待他?

5．表示推测用法时，情态动词过去式往往表示把握性比用现在式时要小：

He may／might be at home now.

He can't／cou|d not have gone off with some friends.

需要注意的是，在推测用法中，can只用于疑问句和否定句，could则无此限定:

我们可以说：They could have gone to London．

不可以说：They can have gone to London.

另外,may用于推测用法时,不用于疑问句。我们不说：

May it rain？

而说： Is it likely to rain，do you think?    ’