Generally we use the passive voice to indicate what happened to the subject of the sentence without saying who or what carried out the action, meaning that in the passive voice (voz pasiva), the subject is acted upon by an outside agent. When the agent is specified, the passive voice is expressed by:
subject + ser + past participle + por + agent.

For example: La mezquita fue construida por el Sultán Hassan (The mosque was built by the Sultan Hassan).

From active to passive voice:

  • Mis amigos quieren a mi perro becomes Mi perro es querido por mis amigos.

Since the past participle acts as an adjective, it agrees in gender and number with the subject. If the passive subject is a thing and the agent is not mentioned, the passive reflexive (pasiva reflexiva) construction is used, with the reflexive pronoun se preceding the verb and the passive subject following it:

  • Allí se hablan muchos idiomas (many languages are spoken there).
  • No se permite hacer modificaciones (making modifications is not allowed).

Note that the Spanish past participle has to agree with the subject in gender and number, just the way it does with adjectives.

Impersonal Constructions in Spanish

Se is also used to form impersonal construction, with se used as an indefinite subject pronoun in Spanish similar to the English “one” or the impersonal “you” and “they”, like: Se habla español (Spanish is spoken / One speaks Spanish). There are two main criteria to be met: the verb must be in the singular, since se is singular when used as a subject pronoun, and se should be easily translated as one or you:

  • ¿Cómo se dice “please” en español? (How do you say “please” in Spanish?)
  • ¿Cómo se va a Madrid? (How does one get to Madrid?)

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