can’t have done表否定推断，推测肯定没做。

　　The measurement couldn’t have been wrong.

　　测量不可能出错了。

　　He can’t have been to that town.

　　他根本不可能去过那座城市。

　　He can't have taken it home.

　　他不可能把它带回家了。

　　can’t have done表不可能。

　　mightn’t have done表可能不。