Oraciones condicionales tipo 3

[A] El verbo de la if-clause está en pretérito pluscuamperfecto; el verbo de la cláusula principal en condicional perfecto. El tiempo es pasado y la condición no puede cumplirse porque la acción de la if-clause no ocurrió.

• If I had known that you were coming I would have met you at the airport. (Pero no lo supe, así que no fui.)
• If he had tried to leave the country he would have been stopped at the frontier. (Pero no lo intentó.)

[B] Variaciones posibles de la forma básica

1 could o might pueden usarse en lugar de would:

• If we had found him earlier we could have saved his life. (capacidad)
• If we had found him earlier we might have saved his life. (posibilidad)
• If our documents had been in order we could have left at once. (capacidad o permiso) 

2 Puede usarse la forma continua del condicional perfecto:

• At the time of the accident I was sitting in the back of the car, because Tom’s little boy was sitting beside him in the front. If Tom’s boy had not been sitting there I would have been sitting in front.

3 Puede usarse el pluscuamperfecto continuo en la if-clause:

• I was wearing a seat belt. If I hadn’t been wearing one I’d have been seriously injured.

4 Es posible una combinación de los tipos 2 y 3:

• The plane I intended to catch crashed and everyone was killed. If I had caught that plane I would be dead now, o bien: «I would have been killed.» (tipo 3)
• If I had worked harder at school I would be sitting in a comfortable office now; I wouldn’t be sweeping the streets. (Pero no trabajé duro en la escuela y ahora estoy barriendo las calles.) 

5 had puede ir colocado al principio y el if omitirse:

– If you had obeyed orders this disaster would not have happened =

= Had you obeyed orders this disaster this disaster would not have happened.