1 When the main interest of the speaker is focused in the complement, and not in the subject of the action, the clause is built with the verb in passive voice. The subject of the passive clause is the patient subject that undergoes the action of the verb; the agent is preceded by the preposition por.
(Yo) he arreglado el coche. (Oración activa)
El coche ha sido arreglado (por mí). (Oración pasiva; el coche es el sujeto paciente; por mí es el complemento agente)
2 The verb in passive conjugate the verb ser, in the tense of the active voice and agrees with the patient subject in gender and number.
| Active voice | Passive voice | |
| Present (ind.) | Yo culpo | Yo soy culpado |
| Future | Yo culparé | Yo seré culpado |
| Perfect (ind.) | Yo he culpado | Yo he sido culpado |
| Indefinite | Yo culpé | Yo fui culpado |
| Present (sub.) | Yo culpe | Yo sea culpado |
Next the past participle of the verb is added. The subject of the active clause changes to agent complement, preceded by the preposition por.
He castigado a Juan.
Juan ha sido castigado (por mí).
3 The passive structures are not used much in Spanish. Many times a passive form is gramatically possible, but theSpanish speaker preffers active structures. The passive tenses are used in formal texts; is a stylistic resource to avoid the monotony. Also, in legal texts the passive is used to despersonalize the judge’s action.
El acusado ha sido condenado a 5 años de prisión. (= In fact was the judge who pronounced sentence.)
The passive clauses are very common in the texts in poorly translated from English.