Third Conditional

 When we are talking about something in the past which cannot be altered now, we use:

If + Past Perfect, would have + past participle

EXAMPLE: If you had studied all of these grammar pages, you would have passed the exam.

You can not alter or change the past. You didn't study in the past (something you cannot change now) so you didn't pass the exam. It is an imaginary situation that didn't happen.

• If you had been more careful, you wouldn't have had an accident.
• If I had seen you, I would have said hello.
• If he had asked me, I would have helped him.
• If you had studied, they would have passed the exam.
• If I had known, I wouldn't have done that.

Notice how this tense can be used to say that you regret doing something or when you are telling someone off (reproaching someone). This type of conditional can also be used when making excuses.

We can also change the word order of the sentence...

Would have + If + past perfect

EXAMPLE: You would have passed the exam if you had studied all of these grammar pages.

• I wouldn't have left my job if I had known how difficult it is to find another one.
• I would have taken a photo if I had brought my camera with me.
• He would have died if the ambulance hadn't arrived quickly.
• She would have gone to your birthday party if she hadn't been sick.
• He wouldn't have become lost if he had taken the map with him.
• The team would have won if the referee hadn't taken the bribe.
• You wouldn't haved needed fillings if you had brushed your teeth more frequently.