Spanish Passive Voice
La voz pasiva (passive voice) is a construction that indicates that the subject is being acted upon by the verb, instead of doing the action.
The "conventional" passive (la pasiva perifrástica)
The conventional passive, also called "la pasiva perifrástica", is formed by the verb ser (conjugated) plus the past participle of the main verb. Let's see how a sentence in voz activa can turn into passive.
"Mis abuelos construyeron esta casa." (active)
My grandparents built this house.
"Esta casa fue construida por mis abuelos." (passive)
This house was built by my grandparents.
Notice that the verb in the first sentence (construyeron), is conjugated in the past tense.
To turn it into the passive voice, we conjugate ser in the past tense (fue) and add the past participle of the main verb (construída), agreeing with the subject (esta casa).
El sujeto agente
What was previously the subject of the sentence in active (mis abuelos) is now what is called "el sujeto agente" (the agent), and it is preceded by "por".
Here are other examples in different tenses:
Mi hermano escribe muchos poemas.(active)
My brother writes lots of poems.
Muchos poemas son escritos por mi hermano. (passive)
Lots of poems are written by my brother.
La policía ha arrestado al sospechoso. (active)
The police have arrested the suspect.
El sospechoso ha sido arrestado por la policía. (passive)
The suspect has been arrested by the police.
To form a conventional passive sentence the agent doesn't always have to be present. Sometimes it is omitted because we don't know it or it is irrelevant.
"El sospechoso ha sido arrestado."
The suspect has been arrested.
English passive voice
In English, the passive voice is constructued using the relevant tense of the verb to be (is/was/will be, etc.) + the past participle of the action verb, the same way we do in Spanish.
However, in English, both direct objects and indirect objects of an active sentence can become the subject of a passive sentence. In Spanish, only direct objects can become the subject of a passive sentence.
Active: They gave a present to the girl. ("Present" is the direct object [DO] and "girl" is the indirect object [IO].)
Passive: A present was given to the girl. ("Present" [DO] becomes the subject.)
Passive: The girl was given a present. ("The girl" [IO] becomes the subject.)
In Spanish this last sentence would be incorrect: "La chica fue dada un regalo" (The girl was given a present.)
Learn more: Introduction to voice