couldn't have done和can't have done都表示不可能,是对过去情况的推测。
例句:He can't / couldn't have worked out the problem.他不可能解决了这个难题。
can't 也可以用于对现在情况推测，couldn't have done可以用 和过去事实相反的虚拟语气。
例如：If you hadn't gone to the party,you couldn't have met your future wife.如果你没去晚会,你不可能遇到你未来的妻子.
