情态动词有没有事态的变化

情 态 动 词 的 时 态

英语中情态动词也象行为动词一样，具有时态的变化。现根据情态动词的功能分述如下：

一、“能力”表示现在或将来的“能力”用can + 动词原形；表示过去的“能力”用could + 动词原形：

A computer can’t think for itself , it must be told what to do .

Can you join us tomorrow?

He could speak five languages when he was young .

表示将来的“能力”时用shall / will be able to 更能把时间关系表示明确。

二、“允许”表示现在或将来的“许可”，陈述句中用 can / may（不用could / might ）+动词原形，疑问句中用can /could / may / might +动词原形；表示过去的“许可”用could / might + 动词原形：

Could / Might / Can / May / I borrow your umbrella?

You may / can watch TV after you finish your homework .

He said I could go with him .

三、“禁止”表示现在的“禁止”用can't / mustn't / may not + 动词原形；表示过去的“禁止”用couldn't / mustn't +动词原形：

The guard said we mustn't / couldn't crossthe border.

You mustn't / can't / may not pick any flowers in the garden .

四、“必须”表示现在或将来的“必须”用must + 动词原形；表示过去的“必须”用had t