从零开始学语法：如何表达本来该做某事？

should have done

“should have + 动词的完成式”表示本应该做而实际上没有做，它的否定形式表示某种行为本不该发生但却发生了。有责备的意味。

You should have started earlier, but you didn't.你本应该早点儿出发，但是你没有。You should have washed the wound.你应该已经洗好了伤口。She shouldn't have taken away my dictionary, for I wanted to use it.她本不应该拿走我的词典，因为我要用它。You shouldn't have been so rude to him.你本不应该对他那么粗鲁。

注：“should have + 完成式”虽然可以表猜测，但因为会造成歧义，应少用。

ought to have done

1、“ought to have + 动词的完成式”表示过去应做某事而实际未做，它的否定形式表示本不应该做某事却做了（用法和should相同）。

You ought to have helped him, but you didn't.你本应该帮助他但你没有。You ought to have studied harder.你本应该更努力学习的。He ought not to have stopped his work halfway.他本不应该做这项工作时半途而废。He oughtn't to have done that.他本来就不该做那件事。

2、“ought to have + 动词的完成式”还可以用来表猜测。

They ought to have arrived by now.现在他们想必已经到达。If he had started at nine o'clock, he ought to have been in London by eleven o'clock.如果他在九点出发，那他十一点钟该到达伦敦了。