Past modal verbs are must, could, might and may with have + past participle to talk about suppositions or speculations regarding a past event. This is called the modal perfect tense.
Here are some examples:
- The cat has escaped – I must have left the window open by mistake.
- Claire has left her handbag here – she must have left in a rush.
- I don’t know why he did that, he could have hurt himself.
“May” and “might” are actually very similar although some people say that the past modal form of “may” has a slightly higher level of probability.
We use the past modal verb form of MAY and MIGHT to speculate about the past
For example, in the above image, we can see two people speculating about why John hasn’t arrived at work yet. The woman suggests that he is late because he missed the train (in the past):
- What isn’t John at work yet?
- I don’t know, he might have missed the train.
The woman could also use the past modal verb form of “may” and it would have the same meaning i.e. a speculation about what happened to John.
- I don’t know, he may have missed the train.
Use MIGHT to talk about something in the past which didn’t happen
remember if we are talking about something that didn’t happen, a possibility in the past we use “might have” and not “may have”:
The car came around the corner so fast that I might have been killed.
The modal perfect continuous
For speculations about a continuous action in the past we can use the modal perfect continuous tense:
MAY/MIGHT + HAVE BEEN + ING FORM OF VERB
They don’t know why he crashed the car but I’ve heard that he may have been drinking and driving
Formation of negative sentences
To form a negative past modal verb sentence simply insert the word “NOT” in between the modal verb and the word “have”:
MAY/MIGHT + NOT + HAVE + PAST PARTICIPLE
Quinoa is a simple food that you may not have heard of.
Negative sentences with past modal verbs
If you want to politely ask somebody as you speculate about what may have happened, you use “Do you think you may/might have + past participle”:
DO YOU THINK YOU + MAY/MIGHT + HAVE + PAST PARTICIPLE
- Do you think you may have added too much water to your plant? It looks quite yellow.
- Do you think she might have forgotten about the appointment? It’s 9:20.
- You’ve been looking all morning, do you think you might have lost your keys?
The past modal form with COULD is used to talk about CAPABILITY in the past
When we talk about ability or capability in the past we can use a form of the conditional perfect.
COULD + HAVE + PAST PARTICIPLE
Here are some examples of could as a past modal verb for capability in the past:
- I could have been a professional dancer, but I broke my leg when I was 17.
- You could have passed your exams if you had studied as I told you!
- he could have asked me to help him build the wardrobe, instead of spending all day doing it by himself.
Negative form to express impossibility in the past
Whereas “may/might not have…” express that something possibly did not happen in the past, “could not have …” means that something definitely did not happen. It was impossible.
COULD (+NOT) + HAVE + PAST PARTICIPLE
Here are some examples for clarity:
- Even if I had studied for 1000 hours I could not have passed that exam! It was too difficult – impossible!
- Wow! 100% on your exam! You could not have done any better – well done!
We use “could have” to offer gentle criticism
If a native English speaker is slightly annoyed with you for not mentioning something important, they might say to you:
- You’re an hour late! You could have let me know!
- You could have sent a message at least!
- She didn’t warn me about the visit, she could have mentioned that they were coming!
The past modal form with MUST is used to talk about what you believe is certain about the past
This can be used in situations where you are very sure about your deductions and believe there are no other possibilities. It has a similar structure to “might/may have” but with much stronger certainty.
MUST + HAVE + PAST PARTICIPLE
Here are some examples of must as a past modal verb expressing sure deductions/beliefs:
- Karen is late – she must have missed her train. (no other explanation is possible)
- I don’t have my keys – I must have left them in the kitchen.
- The bicycle has disappeared – it must have been stolen.
Use “couldn’t have” for negative certainty in the past, not “mustn’t have”
As mentioned before, if we are certain something was impossible or did not happen in the past we must use the past modal verb “couldn’t have,” becausee “mustn’t have” cannot be used with this meaning. Here is an extra example:
- The bicycle couldn’t have been stolen – there was nobody here.
We use the SHOULD in the past modal verb form to talk about past mistakes and make recommendations / strongly criticise past actions.
We can use this past modal when commenting on past errors or to criticize or make suggestions about past behaviour. Using “should” to criticise is stronger than using “could” and more direct.
SHOULD + HAVE + PAST PARTICIPLE
- You should have been here TWO hours ago- sorry there was traffic.
- He should have gone to the doctor immediately instead of waiting.
- She should have added more salt to the food, it tastes bland.
Use “shouldn’t have” in negative sentences expressing past criticism
- We shouldn’t have turned left before, this is the wrong direction.
- You shouldn’t have said that to her, now she’s upset.
- He shouldn’t have gone to work, he was very ill.
The past modal form with WOULD is used to talk about past possibilities and their (unreal) consequences
“Would have” structures are a past conditional (often used together with “if” to form the 2nd conditional), which describe not only a past possibility but also its past potential consequences. Often these consequences can no longer happen in the present, meaning they are describing situations that are unreal or unlikely/impossible to occur now.
- If he had passed his exams, he would have become a doctor (no longer possible now).
- She would have been here earlier but her train was delayed.
- I would have called you but my phone had no battery.
“wouldn’t have” is used for expressing negative past possibilities
- He wouldn’t have crashed the car if he hadn’t drunk so much.
- She wouldn’t have left, if they hadn’t been so rude to her.
- We wouldn’t have chosen this hotel, if we had read the reviews.
Summary of past modal verbs
Essentially, all modals can be used in the past by adding “have + past participle,” however, their meaning and function often change:
- May / Might have = speculating in the past
- Could have = capability in the past
- Should have= criticism / recommendation in the past
- Would have= past possibilities and their (unreal) consequences
For example, see how the following past modals change the meaning of the sentence below:
- I may/might have talked to John… [but not sure]
- I could have talked to John… [was able in the past but probably no longer able now]
- I should have talked to John… [but didn’t, criticising]
- I would have talked to John (if)…. [but didn’t, unreal consequence]
Past modal structures in songs
Speculating and commenting on events that happened in the past is an extremely popular theme in music that we hear all the time. Below are just a few examples of songs that use some of the past modal structures we have reviewed above, feel free to check them out and listen for when the past modals are used. Can you think of any more songs that you like which also use past modals? Leave a comment with your favourites, the Break Into English team would love to listen to your picks!
Rolling In The Deep – Adele
It Must Have Been Love – Roxette
When I Was Your Man – Bruno Mars
P.s. There are also famous scenes from movies that use past modal structures too, do you recognise movie in this clip?
Written by Eliza-laria
Writing team Elizabeth and Ilaria
Two of our best writers worked on this to give you the most effective way of studying and learning about past modal verbs.