Modal verbs are often used to discuss present or future actions, but we use ‘perfect modals’ to talk about actions, events or possibilities in the past. A ‘perfect modal’ is a modal verb combined with a present perfect verb form. We often speak about the past, and we often need to speak about the past in order to explain mistakes or guess about possibilities. The forms used below illustrate the typical uses of perfect modals.
Would / Could / Should / Might / Must / Can’t + Have Done
Would / Wouldn’t have + past participle
We use this form to explain that our choice of action would be different to an action performed by another person. It can only talk about impossible things (past actions performed by another person which we cannot change).
- I wouldn’t have sacked Susan. I would have given her an official warning. (You sacked Susan, but this would be my choice of action)
- The client was 10 minutes late for his appointment, so Paul left the office and went to lunch. I would have waited for at least 30 minutes. (Paul didn’t wait – but this would be my choice of action in the same situation)
- I wouldn’t have paid $500 dollars for that jacket. (You bought it, not me. It looks awful and I would only pay $50)
Could / Couldn’t have + past participle
‘Could’ is the past participle of ‘can’ which is used to speak about ability. When we use ‘could have done’, we use it to speak about actions which a person had the ability to do, but did not do.
- I could have applied for a work visa when I was living in Japan but I decided to return home instead. (I had the ability / opportunity but did not do the action)
- He bought an apartment in London for £500,000 but for the same price he could have bought a beautiful house in the country.
- He could have written the email before lunch, but he decided to do it in the afternoon.
Should (not) have + past participle
This form is used to talk about an action which somebody DID NOT do, but which we think was the correct action, or a good idea.
- He should have bought the VW, not the Fiat. (He didn’t, but I think buying the VW was a better choice)
- He failed his exams last week. He should have studied harder. (He didn’t study hard)
- He shouldn’t have shouted. (He did, but the speaker thinks it was a bad idea)
- He shouldn’t have resigned from his job before he found a new one.” (He resigned, but it was a mistake)
- Paul shouldn’t have shouted at the manager. Now he’s going to get sacked.
Must have + past participle
This form expresses our certainty that something was true.
- “I think Paolo must have killed his wife.” (I am certain this happened)
- “We sent everybody an email, so Paul must have known that the meeting had been cancelled.”
Can’t have + past participle
We use this form to explain that (in our opinion) something isn’t/wasn’t possible.
- You can’t have seen Paolo in the office yesterday; he’s in Brazil on holiday (so it is not possible)
- She can’t have forgotten about the meeting; I sent her an email about it yesterday
- He’s only 20 so he can’t have finished university yet
Might (not) have + past participle
We use this form to talk about past possibilities.
- Paolo might have stolen the money. (It’s possible)
- Paul has visited the company several times, so he might have met the sales manager already.
- Paolo wasn’t at the meeting, but he might not have received the email asking him to attend.
Needn’t have + past participle
This speaks about an action which a person DID do, but which was not necessary.
- It didn’t rain today, so I needn’t have taken an umbrella to work. (I DID take an umbrella, but it wasn’t necessary)
- You needn’t have bought me a birthday present. (Thank you, but it was not necessary)
- Paul’s computer had a virus, but now it has been repaired, so he needn’t have bought a new one.