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When it comes to expressing a personal feeling in front of an event, the shorter, the faster, in a few words, the more idiomatic way is to use a modal auxiliary.
Unfortunately, it’s rarely what comes to our students’ minds! On the contrary, impersonal sentences, such as: ‘it is possible that…/ it is impossible that…/ it is a good idea to…/ It is perhaps true that…’ rush to their minds…
The best thing to do is to work a lot, so that the constructions of past modals become automatic… That’s what we’ll do…
Let’s go bravely! Here, we will revise past modal auxiliaries!
I) THE CONSTRUCTION OF PAST MODALS:
a) modal + have + past participle of the main verb.
The situations happened in the past and can’t be changed:
– He could have fallen dangerously
– She should have warned me!
It’s the same form as in the past contidionals:
– If the flight had been cheaper, I would have taken a direct flight.
b) In conversations, this form is often shortened in “could’ve”, “should’ve”, “would’ve”.
c) To make a negative form, add ‘not’ to the modal:
– modal + not + have + past participle of the verb.
– He shouldn’t have said that.
– She might not have noticed the mistake.
d) In the interrogative form, swap the modal and the subject.
– Should I have told you before?
II) WHAT MODALS MEAN:
➡️ 1) COULD HAVE + PAST PARTICIPLE: something was possible in the past, but didn’t happen,
or there was a probability which didn’t happen.
– He could have stayed, but he left.
➡️ 2) COULDN’T HAVE + PAST PARTICIPLE: something was hypothetically impossible.
– I couldn’ t have succeeded if you hadn’t been here.
➡️ 3) SHOULD HAVE + PAST PARTICIPLE: it was a good idea, which didn’t happen.
– I should have followed your advice.
➡️ 4) SHOULDN’T HAVE + PAST PARTICIPLE: it was a bad idea, and it still happened.
– You shouldn’t have lied to her.
➡️ 5) MUST HAVE + PAST PARTICIPLE: express a high degree of certainty:
(almost a 100% sure)
– I must have left my gloves in the train.
➡️ 6) MIGHT HAVE + PAST PARTICIPLE: less certain than ‘must’:
some past events seemed probable, but not sure.
– She might have met him before.
➡️ 7) WOULD HAVE + PAST PARTICIPLE: we wanted something to happen, but it didn’t, though we would have liked it.
– I would have called him but couldnt find his number.
III) RECAP:
| VERB | MEANING | EXAMPLE |
| Could have done | Ability, probability | He could have spoken (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 helped him (but you didn’t) |
| Shouldn’t have done | Bad idea | You shouldn’t have cheated (but you did) |
| Must have done | Certainty | They must have got lost (I’m sure they did) |
| Might have done | Probability | She might have given up (she probably did) |
| Would have done | Imaginary result | I would have married a Prince (but I didn’t) |
Of course, you only have to understand how this construction works… Then with habit,
it will become quite automatic, and you’ll realise that it was quite easy.
Do not hesitate! Go for the modals! 
End of the free exercise to learn English: Modal auxiliaries in the past.
A free English exercise to learn English.
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