Third Conditional

The Third Conditional imagines an opposite past and its impossible result. We use it for regrets, criticism, gratitude, or simply speculating how things could have turned out differently.

Formula

If + had + V³ → would have + V³

When do we use it?

Regrets & hindsight: If I had left earlier, I wouldn’t have been late.
Blame/criticism: If they had checked the brakes, the accident wouldn’t have happened.
Gratitude: If you hadn’t helped, we would have failed.
Speculation: If dinosaurs had survived, how would the world have changed?
Missed opportunities: If she had applied, she might have got the job.

Syntax details

If we had booked earlier, we would have paid less.
We would have paid less if we had booked earlier.

As with other conditionals, add a comma only when the sentence begins with the if-clause. You can swap would with could or might to change the meaning (ability / possibility).

Affirmative, Negative & Question

Form	Structure	Example
Affirmative	`If + had + V³ … , would have + V³`	If they had saved more, they would have bought a house.
Negative	`If + had not + V³ … , would not have + V³`	If he hadn’t forgotten his passport, he wouldn’t have missed the flight.
Question	`What would have + V³ if + S + had + V³ … ?`	What would have happened if the alarm had gone off?

More examples

If I had known about the traffic, I would have left earlier.
If she had studied harder, she might have passed the exam.
If we had booked tickets, we would have seen the concert.
If they had set an alarm, they wouldn’t have overslept.
If you had told me, I could have helped.
If the weather had been better, we would have gone hiking.
If I had saved more money, I could have bought that car.
If the team had trained more, they would have won the match.
If he had worn a coat, he wouldn’t have caught a cold.
If the software had been tested, the bug wouldn’t have occurred.

Common mistakes

❌ If I would have known, I would have helped.
✅ If I had known, I would have helped.
(No would in the if‑clause.)
❌ If she studied, she would have passed.
✅ If she had studied, she would have passed.
(Use past perfect, not past simple.)
❌ I would have come, if I knew.
✅ I would have come if I had known.
(Past perfect in the condition; no comma when clause is last.)
❌ If it hadn’t rained, we would go.
✅ If it hadn’t rained, we would have gone.
(Use would have for past result.)