The third conditional
The third type of conditional sentences is about unreal conditions in the past. We express that the situation in the past might have developed otherwise, but in reality, it didn't.
To build the third conditional
- we put the verb in the if-part into the past perfect
- and in the second part, which is the consequence of the condition, we use would + have + past participle of the verb.
If {past perfect}, then would + have + {past participle}
Examples
If you had set up the alarm clock, you would have woken up on time in the morning. But you didn't set it up and you woke up too late.
If Timmy hadn't been so nervous during the interview, he would have got the job. But he was nervous and didn't get it.
I would have worked faster if you hadn't bothered me all the time. But you bothered me and I wasn't progressing very fast.
We would have gone for a walk yesterday if it hadn't started to rain. But it started to rain and we didn't go.
She would have bought new headphones if she hadn't spent all her money on a new iPhone. But she bought it and didn't have money to get the headphones.
He would have passed that test if he had been more attentive. But he wasn't attentive and failed the test.
The topic of the third conditionals is closely related to the past modals. Sometimes we can use "could" instead of "would".