过去将来完成时

should / would have done sth.

用法

1、 过去将来完成时表示在过去将来某一时间以前发生的动作，并往往会对过去将来某一时间产生影响。 构造：should / would have done sth.

I thought you'd have left by this time.我想这会儿你已经走了。

He told them he would have finished it by 8 o'clock.他告诉他们他会在8点以前干完。

I guessed that Helen would have told her something.我猜海伦会告诉她一些情况的。

2、 过去将来完成时还常用在虚拟语气中，表示与过去的事实相反。

[注]在当代英语中，大家都用 would (缩略式为 'd)