Past modals
We can use modal verbs with the past participle of the main verb:
modal + have + past participle
We use modals this way when we are talking about the situation that happened in the past and can't be changed anymore.
For example
{mp3}/files/mp3/past-modals/1.mp3{/mp3}You could have hurt yourself.
{mp3}/files/mp3/past-modals/2.mp3{/mp3}They should have warned me.
{mp3}/files/mp3/past-modals/3.mp3{/mp3}He must have got lost.
It is the same form as in the third conditionals.
Compare
{mp3}/files/mp3/past-modals/4.mp3{/mp3}If I had had some cash on me, I would have bought an ice-cream.
{mp3}/files/mp3/past-modals/5.mp3{/mp3}I would have chosen a direct flight if there had been tickets left.
In spoken English, you will often hear shortened forms like could've, should've, would've.
To make a negative form, add "not" after the modal:
modal + not + have + past participle
It is common to use contracted negative forms like couldn't, shouldn't.
Examples
{mp3}/files/mp3/past-modals/6.mp3{/mp3}She shouldn't have said that.
{mp3}/files/mp3/past-modals/7.mp3{/mp3}We couldn't have foreseen that change of plans.
{mp3}/files/mp3/past-modals/8.mp3{/mp3}He might not have noticed the error.
To make a question with a modal verb referring to the past, we swap the modal and the subject:
modal + subject + have + past participle ... ?
Examples
{mp3}/files/mp3/past-modals/9.mp3{/mp3}Should I have called you earlier?
{mp3}/files/mp3/past-modals/10.mp3{/mp3}Would he have believed me?
Meaning of past modals
could have + past participle
Something was possible in the past or there was a probability, but it didn't happen.
{mp3}/files/mp3/past-modals/11.mp3{/mp3}He could have slept till noon but the alarm clock woke him up.
{mp3}/files/mp3/past-modals/12.mp3{/mp3}We could have stayed longer but we decided to leave.
{mp3}/files/mp3/past-modals/13.mp3{/mp3}He could have been seriously injured. Fortunately, nothing happened.
couldn't have + past participle
Opposite to could have: something was hypothetically impossible.
{mp3}/files/mp3/past-modals/14.mp3{/mp3}I can't believe Kevin didn't show up! He couldn't have forgotten about the meeting.
{mp3}/files/mp3/past-modals/15.mp3{/mp3}Thanks for your help! I couldn't have managed without you!
{mp3}/files/mp3/past-modals/16.mp3{/mp3}I checked the equipment many times: it couldn't have failed.
Keep in mind that we don't use "can" as a past modal. However, you can use can't as a synonym to couldn't.
{mp3}/files/mp3/past-modals/17.mp3{/mp3}The boy can't have written such an essay on his own. (= couldn't)
should have + past participle
It was a good idea to do something, but it didn't happen.
{mp3}/files/mp3/past-modals/18.mp3{/mp3}He should have told me that they cancelled the conference.
{mp3}/files/mp3/past-modals/19.mp3{/mp3}You should have come to the party yesterday, it was fun.
{mp3}/files/mp3/past-modals/20.mp3{/mp3}I should have followed your advice, you were right.
shouldn't have + past participle
The addition of "not" reverses the meaning: it was a bad idea to do something, but it still happened.
{mp3}/files/mp3/past-modals/30.mp3{/mp3}I shouldn't have drunk so much coffee before bedtime.
{mp3}/files/mp3/past-modals/31.mp3{/mp3}We shouldn't have tried to fix the car ourselves.
{mp3}/files/mp3/past-modals/32.mp3{/mp3}You really shouldn't have lied. Why didn't you tell the truth?
must have + past participle
We use this modal verb to show a high degree of certainty. We are almost 100% sure that something took place in the past.
{mp3}/files/mp3/past-modals/21.mp3{/mp3}Where are my gloves? I must have left them in the taxi.
{mp3}/files/mp3/past-modals/22.mp3{/mp3}This antique chandelier looks terrific. You must have spent a fortune.
{mp3}/files/mp3/past-modals/23.mp3{/mp3}Phillip called to say he'd be late. He must have missed the train.
might have + past participle
Might expresses less certainty compared to must. We say "might have done" when some past event seems probable but we aren't absolutely sure.
{mp3}/files/mp3/past-modals/24.mp3{/mp3}They might have misunderstood us.
{mp3}/files/mp3/past-modals/25.mp3{/mp3}She might have met him yesterday.
{mp3}/files/mp3/past-modals/26.mp3{/mp3}It might have slipped his mind.
We can also say may have done with the same meaning but might is more common.
would have + past participle
When we wanted something to happen but it didn't happen in the end, we use would + have + past participle.
It has the same meaning as in the third conditional sentences.
{mp3}/files/mp3/past-modals/27.mp3{/mp3}I would have telephoned that company, but there wasn't a phone number on their website.
{mp3}/files/mp3/past-modals/28.mp3{/mp3}He would have taken a warm coat, but he didn't see the weather forecast.
{mp3}/files/mp3/past-modals/29.mp3{/mp3}She would have got a pay raise if she had been more persistent.
Pay attention
Try to express probability using modal verbs instead of long complex sentences like "It is possible that..." / "It is probable that..." / "I am sure that...". The shorter the sentence, the more natural and "native" it sounds.
To recap, let's put all the past modals into a table.
| Verb | Meaning | Example |
|---|---|---|
| could have done | ability, probability | He could have called me (= but he didn't) |
| couldn't have done | impossibility | It couldn't have snowed in June (= but it did) |
| should have done | good idea | You should have spoken to your boss (= but you didn't) |
| shouldn't have done | bad idea | You shouldn't have shouted at your boss (= but you did) |
| must have done | certainty | They must have got lost (= I'm sure they did) |
| might have done | probability | She might have missed your call (= she probably did). |
| would have done | imaginary result | I would have relocated (= but I didn't) |