(Si lo hubiéramos sabido antes, habríamos elegido de manera diferente.)
| Time reference | Verb in main clause | Verb in conditional clause | ||
|
past |
would (might, could) + have + past participle |
Past perfect |
| If we had known in advance, we would have chosen differently. (Si lo hubiéramos sabido antes, habríamos elegido de manera diferente.) |
| They wouldn't have written the letter if they had known the facts. (No habrían escrito la carta si hubieran conocido los hechos.) |
| If they had been working when we came home, somebody would have seen them. (Si hubieran estado trabajando cuando llegamos a casa, alguien los habría visto.) |
You will sometimes meet third conditionals without if and with the auxiliary before the subject, e.g.:
| Had we known in advance, we would have chosen differently. |
However, you can always use the forms with if.
