# Modal Verbs in the Past: must have, should have

https://langs123.com/en/english/modals/modal-perfect/
CEFR B2–C1 · 2026-10-19 · CC BY 4.0, langs123 contributors (https://creativecommons.org/licenses/by/4.0/)

> Must have, can't have and might have for deductions about the past; should have for regret and criticism; needn't have for an unnecessary action. The modal and have never change, and the main verb is a past participle: She must have left. You should have called.

## Cheatsheet

| Point | Rule | Example |
| --- | --- | --- |
| Form | subject + must / should / could + have + past participle; have never changes | She should have called. |
| Deduction: sure | must have: it happened; can't have: it did not | She must have left. / He can't have known. |
| Deduction: possible | may have, might have or could have: perhaps it happened | They might have missed the bus. |
| Regret and criticism | should have: not done; shouldn't have: done and wrong | I should have asked. / I shouldn't have shouted. |
| Unused chance | could have or might have: a chance that nobody took | You could have told me. |
| Unneeded action | needn't have: it was done and was not necessary | I needn't have hurried. |
| Unreal past | would have for the result of an unreal past condition | If I had known, I would have called. |
| Passive and continuous | after any modal: have been + past participle / V-ing | It must have been lost. / She can't have been sleeping. |
| Adverb inside | may well have: quite likely; can't possibly have: impossible | She may well have forgotten. / You can't possibly have finished. |
| Expectation and estimate | should have: expected by now; would have: an estimate | It should have arrived by now. / That would have been ten years ago. |
| Plan that failed | was to have + past participle: planned, but it did not happen | The bridge was to have opened in May. |
| Trap | write have or 've, never of | You should've called. |

## Form: the modal perfect

| Form | Pattern | Example |
| --- | --- | --- |
| Affirmative | subject + must / should / could / might + have + past participle | She should have called. |
| Negative | subject + can't / couldn't / shouldn't / needn't + have + past participle | You shouldn't have waited. |
| Question | Should / Could / Would + subject + have + past participle | Should I have called? |

- The modal and have keep one form for every subject: I should have gone. / They should have gone.
- may and might take not as a separate word: She might not have heard.

## Form: short forms

| Full form | Short form | Example |
| --- | --- | --- |
| should have | should've | You should've left early. |
| must have | must've | She must've left early. |
| could have | could've | We could've stayed. |
| might have | might've | It might've rained. |
| would have | would've / 'd have | I'd have gone. |

- Short forms belong to speech and informal writing; formal writing keeps the full form.

## Pronunciation: have after a modal

| Form | Sound | Example |
| --- | --- | --- |
| should have | /ʃəd əv/ | You should have called. /juː ʃəd əv ˈkɔːld/ |
| must have | /məst əv/ | She must have left. /ʃi məst əv ˈleft/ |
| could have | /kəd əv/ | We could have won. /wi kəd əv ˈwʌn/ |
| can't have | /kɑːnt əv/ (US: /kænt əv/) | He can't have known. /hi ˈkɑːnt əv ˈnəʊn/ |
| needn't have | /ˈniːdnt əv/ | I needn't have gone. /aɪ ˈniːdnt əv ˈɡɒn/ |

- After a modal, have is weak, /əv/: it sounds like of but is written have or 've.
- In a statement the past participle takes the stress; the modal and have are weak.

## Use: deduction about the past

| Use | Pattern | Example |
| --- | --- | --- |
| Sure it happened | must + have + past participle | Their car has gone, so they must have left. |
| Sure it did not happen | can't / couldn't + have + past participle | He can't have known. Nobody told him. |
| Possible that it happened | may / might / could + have + past participle | She might have missed the train. |
| Possible that it did not happen | may not / might not + have + past participle | They might not have heard the bell. |
| An activity in progress | must + have been + V-ing | They must have been waiting for hours. |

## Use: criticism and regret

| Use | Pattern | Example |
| --- | --- | --- |
| A good action that was not done | should / ought to + have + past participle | You should have asked first. / I ought to have saved more. |
| A bad action that was done | shouldn't + have + past participle | I shouldn't have shouted at her. |
| A chance that nobody took | could / might + have + past participle | You could have told me. / You might have told me! |

- might have blames more strongly than could have.

## Compare: needn't have and didn't need to

| Point | needn't have | didn't need to |
| --- | --- | --- |
| Meaning | it was done, and it was not necessary | it was not necessary; it may not have happened |
| Example | I needn't have brought a coat. It was warm. | I didn't need to bring a coat, so I left it at home. |
| Example | — | I didn't need to bring a coat, but I brought one. |

- For the present forms of need see Need and Dare.

## Compare: could, was able to and could have

| Point | could | was able to | could have |
| --- | --- | --- | --- |
| Meaning | general ability in the past | success on one occasion | an ability or chance that was not used |
| Example | I could swim when I was five. | I was able to swim across the lake yesterday. | I could have swum across, but I was tired. |

- See Can and Could.

## Use: hypothetical past

| Use | Pattern | Example |
| --- | --- | --- |
| The result of an unreal past condition | would + have + past participle | If I had known, I would have called. |
| A result with no if-clause | would + have + past participle | I would have helped, but nobody asked me. |
| What would not have been possible | wouldn't / couldn't + have + past participle | We couldn't have won without her. |
| A comparison with what might have been | would / could + have been + adjective | It would have been better to wait. / It could have been worse. |
| A possible result, less sure than would have | might + have + past participle | If he had tried harder, he might have won. |

- The if-clause takes the past perfect: if + had + past participle. See Conditionals.

## Form: passive and continuous

| Use | Pattern | Example |
| --- | --- | --- |
| Passive: sure it happened | must + have been + past participle | The window must have been left open. |
| Passive: something that was not done | should + have been + past participle | You should have been told earlier. |
| Continuous: possible | might + have been + V-ing | He might have been working late. |
| Continuous: sure it did not happen | can't + have been + V-ing | She can't have been sleeping. The light was on. |

## Adverbs inside the modal perfect

| Use | Pattern | Example |
| --- | --- | --- |
| Quite likely it happened | may well / might well + have + past participle | She may well have forgotten. |
| A slight chance it happened | may just / might just + have + past participle | The shop might just have closed. |
| Almost sure it did not happen | can hardly / can scarcely + have + past participle | He can hardly have meant it. |
| Sure it did not happen, with emphasis | can't possibly / couldn't possibly + have + past participle | You can't possibly have finished already. |
| Sure it happened, with emphasis | must surely + have + past participle | They must surely have heard the noise. |

## Use: expectation and estimate

| Use | Pattern | Example |
| --- | --- | --- |
| An expected result by now | should + have + past participle | The parcel should have arrived by now. |
| An estimate about the past | would + have + past participle | That would have been about ten years ago. / She would have been twenty then. |
| An assumption about a finished action | will + have + past participle | You'll have heard the news. |

- For will in assumptions see Will and Shall.

## Use: duties, plans and reports

| Use | Pattern | Example |
| --- | --- | --- |
| A duty that was not met | was supposed to have + past participle | She was supposed to have called me by noon. |
| A plan that did not happen | was to have + past participle | The bridge was to have opened in May. |
| A plan made before another past event | had been due to + V | The train had been due to leave at six. |
| Reported speech | the modal perfect does not change | You should have called. → He said I should have called. |

## Typical errors

| ✗ | ✓ | Rule |
| --- | --- | --- |
| You should of called. | You should have called. | write have or 've, which sounds like of |
| She must had left. | She must have left. | have never changes after a modal |
| He should have went home. | He should have gone home. | have + past participle |
| He mustn't have known. | He can't have known. | sure it did not happen: can't have or couldn't have |
| I needn't have gone, so I stayed at home. | I didn't need to go, so I stayed at home. | needn't have means the action was done |
| If I would have known, I would have called. | If I had known, I would have called. | the if-clause takes the past perfect, with no would |
| The keys must have been losing. | The keys must have been lost. | passive: been + past participle; continuous: been + V-ing |
| He can't hardly have known. | He can hardly have known. | hardly is already negative: no second negative |