学习英语需要多读多看，掌握学习技巧。新东方在线小学频道整理了<2020小学英语语法专题：如何表达本来该做某事?>，供大家参考。

　　2020小学英语语法专题：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 didnt.

　　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 shouldnt 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 shouldnt 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 didnt.

　　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 oughtnt 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 oclock， he ought to have been in London by eleven oclock.

　　如果他在九点出发，那他十一点钟该到达伦敦了。

　　小升初英语语法零基础：may have done用法小结

　　may/might have done 推测过去

　　may/might+动词的完成式表示对过去发生的行为的推测。例如：

　　-Whatever has happened to George?

　　-乔治发生了什么事?

　　-I dont know. He may have got lost.

　　-我不知道，他可能迷路了。

　　You might have read about it in the papers.

　　你可能在报上已经看过这个消息了。

　　(之前我们做过can have done用法小结，can have done表推测时都是对过去进行推测，但是may have done不仅可以推测过去)

　　may/might have done 推测现在

　　may/might+动词的完成式表示对现在情况的推测。例如：

　　She might have got up now.

　　现在她可能已经起床了。

　　may/might have done 预测未来

　　may/might+动词的完成式表示推测将来某时之前的情况。例如：

　　He may have left when you get there.

　　等你到达的时候他可能已经离开了。

　　注意：may have done 和 might have done 表推测时，might 所表示的可能性比 may 小，语气较委婉：

　　How quickly time passed! It might have happened yesterday.

　　时间过得好快啊!这事好像就发生在昨天。

　　He might have seen the surprise in my face.

　　他或许已经看到了我惊异的表情。

　　might have done 表轻微责备

　　might have done 除了能够表推测，还能表示过去本来可以做而实际并没有做。这时带有轻微的责备之意。例如：

　　The proposal might have been refused.

　　这个建议本该拒绝的。(有轻微的责备之意)

　　I might have taken another path.

　　我本可以走另一条路。

　　may not/mightnt have done 表可能不

　　之前我们讲到过 cant/couldnt have done 是表示不可能，而 may not/mightnt have done 则是表示可能不，要注意区分哦：

　　He cant have been at the meeting， hes on a business trip this week.

　　他不可能有出席会议，他这周出公差。

　　We couldnt have done it without you.

　　没有你我们肯定完成不了。

　　They may not have known it beforehand.

　　他们事先可能不知道这事儿。

　　They mightnt have regarded me as their friend.

　　他们可能没有把我当作朋友看待。

　　以是<2020小学英语语法专题：如何表达本来该做某事?>的内容，更多小学英语学习资料以及学习技巧请关注新东方在线小学网。