Modal verbs, as per its name, indicate modality (like permission, necessity or suggestion) in the English language. These are auxiliary verbs, so they need a main verb to be paired with, except in the case of answering a yes/no question, and they can’t ever have a tense conjugation like –ed or –ing and, like all auxiliary verbs, they always go before the main verb in the clause, and before the subject in interrogative questions.

For modal perfects, they are used to speak about the past, specifically for hypothetical situations or about regrets the speaker wishes they have happened differently.

Structure of modal perfect verbs

Subject + modal verb with have + main verb (past participle) + rest of sentence

Elisabeth should have thought about that before going out.
I think we must have missed a vital clue to solve this riddle.
Freire could have been wrong before, but not after everything she has studied.
My parents would have arrived sooner, but the blizzard outside must have slowed them.

Could have

Could have expresses:

1. Something that was possible in the past but it didn’t come into reality:

Isildur could have thrown the ring into the fire, but didn’t.
I could have easily won the race but I guess we will never know.
Samantha was a good politician, she could have achieved great things.
They could have arrived on time, but they enjoy chatting outside the door too much.

2. Guessing about something that happened before the present.

John is late, he could have fell down that sinkhole in the road.
For all we know, Kevin could have bought a new suit and never wore it.
I guess Ellen could have arrived on time, but she left her phone at home, so we don’t know.
After escaping, the T. Rex could have attacked the jeeps and fled the scene in no time.

3. In the negative form, couldn’t have is used for situations that weren’t possible in the past, even if the speaker wanted them to be so.

I couldn’t have known interfering with the past would have consequences in the present.
It was a really exhausting race, Sarah couldn’t have won it either way.
With that writing you couldn’t have written a best-selling novel, no matter how great the plot was.
She couldn’t have reached the shore on her own as she couldn’t swim very well.

Would have

Would have expresses:

1. A willingness to do something that was not done in the past.

I would have finished the project on time, but there was this Star Trek marathon and…
Sonya would have finished Kano on their fight, but the screenwriter didn’t allow it.
Deanna would have seen the patient as soon as possible, but she had other duties to attend to.
Pablo would have lifted weights all day, but sadly today was leg day and that took priority.

2. A change in a past situation that results in a different outcome (see: Third conditional)

Tanya wouldn’t have betrayed her kingdom if she had stayed on the court.
If we had listened, the studying plan would have gone smoothly.
Lance would have obeyed his master if the squirrel hadn’t appeared by surprise, distracting the dog.
If she had sewed the dress by herself she wouldn’t have needed the help of the singing, talking animals.

Should have

Should have expresses:

1. Regrets or expectations for things in the past we wish went different

I’m late for the test, I should have set up my alarm clock earlier.
Daniela should have been aware of the dinner before it burned down.
I shouldn’t have trusted you after meeting you at the back alley of the pub that night.
With all that has happened it is clear you should have done things differently regarding your ex.

2. Similar to regret, it can be used as a form of apology.

I’m sorry for spilling the tea, I should have been more careful.
I should have thought about handling your miniatures with care, my apologies.
She should have looked both sides before crossing the street, it won’t happen again.
I should have known how to behave in front of the Pope and the other world leaders, I’m so sorry.

3. Advice or, more specifically, feedback.

This is a good grammar exam, but you should have added some vocabulary questions.
Although she is a great chef, Amanda should have refused to cook for Sophia.
I believe you should have added some more colour in those areas of the painting for a better composition.
f you want my advice, I’d say you should have started the project from a different perspective.

Must have

Must have expresses:

1. A certainty regarding events in the past.

Henry isn’t here, he must have fled when he knew we were coming.
After casting the curse, Regina must have known we would stop her.
Emma must have defeated the dragon by herself, because I don’t hear it roar anymore.
Seeing as we remember our lives, the dark curse that afflicted us must have finally been broken.

Can’t have

Can’t have expresses:

1. A certainty that something did not happen in the past.

It can’t have been easy to reject Laura, knowing that you liked her so much.
I can’t have written that book all by myself, someone must have helped me.
Sorry but I don’t believe you. That situation cannot have happened in the way you are narrating it.
Elsa is a sweet little child, she can’t have spoken to you in that awful manner and with those words.

Uses of might/may have

Might have and may have express:

1. A guess about events that probably happened in any moment in the past.

I might (or might not) have lost your child in the shopping mall this afternoon.
The blind witch may have built that house made of candy to attract children to eat them.
Sally may have prepared soup for our Christmas dinner because that’s her speciality.
Lucy might have contributed to the charity event already, I don’t have the list with the contributors yet.

Modal perfect verbs - Level II