A. 我們常會依照我們現今的狀況來推斷過去的情況.而種種不同的詞則說明我們對一過去事情有多大的把握(100%為最有把握):

肯定詞                       否定詞

must have        100%         can’t have

had to have        |            couldn’t have

may have         |            must not have

might have        |            may not have

could have       0%           might not have 

People in Sweden can only enjoy two months of warm weather (July and August) throughout the whole year.

推測: (很肯定) My friends must have enjoyed their summer when they were living there. They say it’s the most beautiful time in Sweden.

     (較不肯定) They may have had a hard time adjusting to their cold weather the rest of the year.

The Netherland has claimed many of its land from the sea.

(很肯定) They can’t have claimed this much land if they didn’t have the technology to do so.

(較不肯定) They may not have been able to enjoy a better living standard if they didn’t have more land to live on.

B. 問句: 1) could have

John: Could they have arranged this surprise party for Jane? 或 Do you think they arranged the party?

May: They could have. / They couldn’t have.

    2) could have + be

Danny: Could she have been here earlier? 或 Was she here?

Steve: She certainly could have.