Perfect modals express: past possibilities or deductions, The structure is modal+ have+ past participle verb, Possibility in past (not done)= could have, Certainty= must have, Impossibility= can't have, Regret or criticism= should have/ ought to, Lack of necessity= didn't need to/ needn't have, Didn't need to: (We don't know if the action was done, it wasn't necessary), Needn't have: (Action done but unecessary), Speculation in past= might/ may/ could have, She must have gone to sleep, They might have broken up, He should have saved more money, She might have been responsible for the project, So, she can't have passed the exam, I shouldn't have gone to that party, They should have woken up early, The food must have been mouth‑watering, But, she could have taken a taxi, I needn't have studied so much, They must have been traveling, He might have kept up with her life, So the bosses may have been sour‑faced, She must have eaten them, That can’t have been my assignment

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