Should have, could have and would have let you look back at the past and talk about things that did not happen: regrets, missed chances and results that were possible but never came true. The form never changes: modal + have + past participle.
The pattern
I should have left earlier.
We could have taken the train.
If I had known, I would have called you.
01Should have: regret and criticism
Use should have + past participle when something was a good idea but didn't happen. Use shouldn't have when something happened and it was a bad idea. About yourself, it sounds like regret. About other people, it sounds like criticism.
- I should have saved my work before the power went out.
- You shouldn't have paid full price for that couch.
- We should have booked the hotel sooner. Now everything is sold out.
02Could have: missed chances
Could have means something was possible in the past, but it didn't happen. It often describes a missed opportunity or a lucky escape. "You could have told me!" is a complaint: you had the chance and didn't take it.
Couldn't have means something was impossible.
- I could have gotten a job in Seattle, but I stayed in Dallas.
- Watch out! You could have hurt yourself.
- I couldn't have finished the move without your help.
03Would have: the result that never happened
Would have describes an imagined past result. It didn't happen because the condition wasn't true. It often follows an if clause with had + past participle (the third conditional), but the condition can also be understood from context.
- If you had asked, I would have helped.
- I would have called, but my phone died.
- She'd have loved this restaurant.
| Form | Meaning | Example |
|---|---|---|
| should have done | a good idea that didn't happen | I should have studied. |
| shouldn't have done | a bad idea that happened | I shouldn't have said that. |
| could have done | possible, but it didn't happen | We could have won. |
| couldn't have done | impossible | I couldn't have done it alone. |
| would have done | an imagined result | I would have come. |
04How it sounds and how to write it
In fast speech, have shrinks to a tiny sound: should've, could've, would've, which sound like "shoulda," "coulda," "woulda." Because of this, many people write should of, but that is always wrong. In writing, use should have or should've.
- I should've known.
- You could've asked me.
- It would've been fun.
05Common mistakes
I should of called you.
I should have called you.
Of sounds like the weak form of have, but after a modal you always write have.
You should have came earlier.
You should have come earlier.
After have, use the past participle (come), not the past simple (came).
We could went to the beach.
We could have gone to the beach.
A past possibility needs could have + past participle.
If I would have known, I would have come.
If I had known, I would have come.
You will hear the first one in casual speech, but in writing the if clause takes had.