1) may(might) have + done sth, can (could) have + done sth　表示过去，推测过去时间里可能发生的事情。
　　Philip may (might) have been hurt seriously in the car accident¹.
　　Philip can (could) have been hurt seriously in the car accident.

2)　must have +done sth，对过去时间里可能发生的事情的推测，语气较强，具有"肯定"，"谅必"的意思。
　---Linda has gone to work, but her bicycle is still here.
　---She must have gone by bus.

3) ought² to have done sth, should have done sth
　　本应该做某事，而事实上并没有做。否定句表示"不该做某事而做了"。
　　You ought to (should) have been more careful in this experiment³.
　　He ought not to have thrown the old clothes away.（事实上已扔了。）
　　ought to 在语气上比should 要强。

4) needn't have done sth　 本没必要做某事
　　I dressed very warmly for the trip, but I　needn't have done so. The weather was⁴ hot.

5) would⁵ like to have done sth　 本打算做某事　
　　I would like to have read the article⁶, but I was very busy then.

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