Modals have no past form of their own. To talk about the past, use modal + have + past participle.
| form | meaning | example |
|---|---|---|
| should have + p.p. | it was a good idea, but you didn't (regret, criticism) | You should have told me. |
| must have + p.p. | I'm almost sure it happened | The streets are wet — it must have rained. |
| can't / couldn't have + p.p. | I'm sure it didn't happen | She can't have seen us. |
| might / may / could have + p.p. | perhaps it happened | He might have missed the train. |
| could have + p.p. | it was possible, but it didn't happen | You could have hurt yourself! |
| would have + p.p. | imagined past (conditional 3) | I would have helped you. |
| needn't have + p.p. | you did it, but it was unnecessary | You needn't have brought a gift. |
For real past obligation and ability: had to (I had to work late), could / was able to (I could swim at five; I was able to fix it — one specific success), didn't have to (it wasn't necessary, so I didn't).
In speech, “have” is reduced: should've, must've, could've — never write “should of”.
Translate the words from your reading, review them as flashcards and practise with gap-fill sentences.
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