What is the Third Conditional?
The third conditional refers to imaginary situations in the past. We use it to speculate about things that did not happen, and to imagine a different outcome. It often expresses regret or criticism.
IF clause: if + past perfect (had + past participle)
Main clause: would have / could have / might have + past participle
Examples
If I had studied harder, I would have passed the exam. (I didn't study, so I failed)
She would have gotten the job if she had arrived on time. (she was late)
If he had saved more money, he could have bought a car. (he didn't save)
We wouldn't have gotten lost if we had used the map. (we didn't use it)
Contractions in Speech
In spoken English, had and would have are often contracted.
If I'd known, I would've told you. (= If I had known, I would have told you.)
She'd have come if she'd been invited. (= She would have come if she had been invited — 'd can mean would or had.)
⚠ Common mistake: Do NOT use would have in the if-clause.
✗ If I would have known, I would have called.
✓ If I had known, I would have called.