This type 3 conditional expresses a situation in the past that did not happen, so when we use this conditional we are actually imagining a different past that cannot be changed. This unreal situation can never happen, not now or ever.


Conditional Clause Main Clause
If + past perfect tense would / could / might 
If you had watched the match, you would have known how exciting it was.


With this conditional, we use the past perfect in the conditional clause and the perfect conditional (would have + past participle) in the main clause to:


1. express disappointment or regret about things that are not possible to happen now.


  • If you had married his brother instead of him, you could have been a happier person.
  • If you had taken up teaching, you would have been better off.



2. talk about things that should have happened in the past but didn't. 


  • If he had gone to the doctor earlier, he wouldn’t have got this disability.
  • If I had completed my education, I would have been a person of importance or authority.



3. imagine unrealistic situations.


  • If I had been taller, I would have been a professional basketball player.
  • If I had been a businessman, I wouldn’t have led a struggling life.



4. express criticism. 


  • If he had got up earlier, he wouldn’t have missed the bus.
  • If you had been a bit more patient, you would have got what you wanted.



Other modal verbs such as could and might can also be used in the main clause.  


  • If I have known about it, I could have done something to help.
  • If the police had arrived earlier, they might have apprehended the thief.