might not have done/could not have done

我们已经知道,could + 完成时不定式和 might + 完成时不定式都可以表示对过去可能发生的事件的推测。在这个意义上 could 和 might 是可以互换的：

1. You might have dropped it somewhere. 你可能把它丢在什么地方了。

2. She could have gone off with some friends. 她可能跟几个朋友出去了。

但是,couldn't have done 与 might not (mightn't) have done 的意思可就不同了。前者表示“不可能做了某事”(not 是否定 could 的),后者则表示“可能没有做过某事”(not 是否定其后的实义动词的)。请对比下面的实例：

1. They couldn't have left so soon. 他们不可能那么早就走了。

2. Ann couldn't have seen Tom yesterday. 安昨天不可能见到汤姆。

3. ... her father could not have made such a mistake. ……她父亲不可能犯这样的错误。

4. She could not have been more than sixteen ... 她那时不可能超过 16 岁……

5. We could not have heard them because of the noise from the river. 由于河水的声音我们当时不可能听到他们的谈话。

6. You might not have met my grandfather. 你可能没见过我的祖父。

7. Ann might not have seen Tom yesterday. 安也许昨天没有见到汤姆。

8. She mightn't have known what the bottle contained. 她也许不知道这个瓶子里装着什么。

9. They might not have considered me as their friend. 他们可能未把我看作是他们的朋友。

句意他不可能犯那个错误！(2)他或许没有犯那个错误！