The past conditional describes a past situation that never happened, or it did happen and the person speaking is describing the possibility of something not happening in the past. This is also called the past unreal or the past contrary-to-fact.
Here’s an example:
If I had gone to that party, I would have had a good time.
(situation: I didn’t go to the party; therefore, I didn’t have a good time.)
"If I had gone to that party" uses the past perfect in this part of the sentence.
"I would have had a good time" is the likely result.
Sometimes you can do this without "if" and just use the past perfect:
Had I heard the weather report, I would have taken an umbrella.
If I had heard the weather report, I would have taken an umbrella.
These are both good sentences, but the second one is used more often.
Click on the video below:
Here are some more examples:
If she had been more careful, she wouldn’t have spilled her coffee.
(She wasn’t careful, and this is the result. You can’t change the past, but you can talk about it.)
If Stephanie hadn’t climbed up the tree, she wouldn’t have fallen down and broken her arm.
(But, in fact, she climbed the tree, fell down and broke her arm)
If he had given up smoking, he wouldn’t have died at such an early age.
(He didn’t give up smoking, and then he died because of this fact.)