3rd Conditional

The 3rd Conditional is also called the past unreal conditional.
This conditional is used in the past. 

 
STRUCTURE 

If  +  Subject  +  Had  +  Past Participle,
+  Subject  +  Modal  + Have + Past Participle

Examples:        

Could 

If I had known about the party, I could have gone. 

Should

 If you had known about the party, you should have told me.

 Might

 If he had known about the party, he might have gone.

 Would 

If I had known about the party, I would have gone.

USES

 Imaginary situations in the past

This includes actions that did not happen in the past.

Examples:  

• If I had gone to university, I would have studied medicine.
  
• If You had gone to the party, you would have met him.
  

Advice in the past 

These sentences usually don't have an "if" clause, and can often be more direct.

Examples:  

• You should have saved your money.
  
• You should not have gone with him.
  

Describes what you would have done differently

Example:  

• If I had been you, I would not have bought those shoes.
  
• If I had thought about it, I wouldn't have eaten so much.
  

Questions

Here are some examples of questions with the 3rd conditional:

• What would you have done if you had been me?
  
• Would you have finished if you had had more time?
  
• Would you have bought something cheaper?
  
• Should we have paid more attention in class?