Quick explanation: "Passive" sentences can be understood best by contrasting them with "active" sentences. They can express the same idea, but the subject receives the action instead of performing it. Let's take a look at the following two sentences:

El Doctor Gupta examinó a este paciente.
Doctor Gupta examined this patient.

Este paciente fue examinado por el Doctor Gupta.
This patient was examined by Doctor Gupta.

In the first sentence, Doctor Gupta is the subject. He is the one who does the examination, the action which is expressed by the verb. In the second sentence, the patient is the subject, but the patient doesn't do the examination. Notice that if we look back to the first sentence, the patient was the direct object. It is what the doctor who did the examination. Now we can see a pattern. The direct object of the "active" sentence becomes the subject of the "passive" sentence. The doctor, the doer of the action, who is the subject of the "active" sentence is expressed in the "passive" sentence by a prepositional phrase ("by" is a preposition). In spanish we refer to the "doer" of the action as the "agent".

Long Explanation:
In some "passive" sentences, the agent, or the "doer", isn't mentioned at all. For example, we could have a "passive" sentence such as this:

• La madera ha sido cortada.
  The wood was cut.

In this sentence we are telling when that the action took place, but we aren't saying anything about who was responsible for doing it. This is a very important concept for us to keep in mind when we construct "passive" sentences in Spanish. We have to watch if the "doer" of the action is specified in the sentence. If the "doer" is not specified, we will not use the actual "passive" form of the sentence in Spanish. We will use another form, the "reflexive" or in other cases we will use "they". You should remember these sentences. We only use the true "passive" form if the "doer" of the action is specifically stated (or in some cases, "understood" by the listener, but we won't get into that complication in this lesson). Notice that it seems logical in English to say that someone washes himself, but it seems a little odd to the ear of someone who speaks English to say that the wood cut itself. In Spanish we use reflexive sentences that are literally true, and also we use the reflexive form, in a symbolic way, to express "passive" ideas when the "doer" of the action isn't specified. Let's see the active form.

Se cortó la madera.

In the examples which we saw above, the subject of the "passive" sentence (which is the direct object of the "active" version of the sentence) is a thing. We can have people as the subject of "passive" sentences also. First, let's take a look at the following "active" sentence.

• La profesora castigó a la chica.
  The teacher punished the girl.

*IMPORTANT NOTE* You should remember that in Spanish, when a specific human being is the direct object of the verb, we use the preposition "a", although it would not really be translated as "to" in the English version of the sentence.

The "passive" version of this sentence would be:

• La chica fue castigada por la profesora.
  The girl was punished by the teacher.

Again, remember that the teacher is the "doer" or as we say, the "agent" in this sentence. The girl, although in the "passive" sentence, she is the subject, is not the person who is doing the action. She is NOT punishing someone. The TEACHER is punishing the GIRL.

Now, when we construct a "passive" sentence in Spanish we use the ver "ser", not the verb "estar". We'll talk more about that later. Notice that we are talking about an event which took place at a specific moment in the past so we are going to use the preterite past tense form of "ser". Also, the main verb of the "active" sentence is going to be used in the "passive" sentence as the participle. You should remember that this is the form of the verb which normally ends in "-do". However, look at what we have in the Spanish translation of this sentence:

• La chica fue castigada por la profesora.

Notice that instead of "castigado", we have used "castigada". Why do you suppose that this happened? Let's look at another "passive" sentence. Study the following:

• El chico fue castigado por la profesora.
  The boy was punished by the teacher.

We can see that the "participle" (the "-do" form of the verb) will change to match the noun which it describes, which in a "passive" sentence is the subject. What would happen if we had a plural subject? Let's look at the next examples:

• Los chicos fueron castigados por la profesora.
  The boys were punished by the teacher.

We had to change the verb "fue" to the plural form "fueron" (from "he was" to "they were"), and we had to make the "participle" plural to match the subject of the "passive" sentence.

Now let's look at another "passive" sentence.

• Las chicas fueron castigadas por la profesora.
  The girls were punished by the teacher.

We have to keep in mind that in addition to the verb "ser" matching the subject, the "participle" must also match.

You should know how to express ideas in Spanish which in English are in the passive form. The two important things to keep in mind are:

• Is the "doer" expressed in the passive sentence?
• Are we speaking of people or things?

Remember, we only use the true passive construction in Spanish if the "doer" of the action is specified.

EXAMPLES:

• Juan rompió la ventana.
  John broke the window.(active)
• La ventana fue rota por Juan.
  The window was broken by John.(passive)

Notice that the form of the participle will match the item that has been affected.

EXAMPLES:

• Juan rompió las ventanas.
  John broke the windows.(active)
• Las ventanas fueron rotas por Juan.
  The windows were broken by John. (passive)

If no "doer" (in this case, John) is specified, instead of using the true passive construction, we use a reflexive sentence.

EXAMPLES:

• Se rompió la ventana ayer.
  The window was broken yesterday.
• Se rompieron las ventanas ayer.
  The windows were broken yesterday.

Notice that if we are speaking of more than one thing, we use a plural verb in the reflexive sentence.

If we are speaking of people, the situation is slightly different. For true passive sentences we follow the same pattern.

EXAMPLES:

• Los bomberos salvaron a la víctima.
  (active)The firemen saved the victim.
• La víctima fue salvada por los bomberos.
  (passive) The victim was saved by the firemen.
• Los bomberos salvaron a las víctimas.
  (active)The firemen saved the victims.
• Las víctimas fueron salvadas por los bomberos.
  (passive) The victims were saved by the firemen.

However, when we don't mention the "doer" and express the passive idea with a reflexive sentence, we do NOT match the verb to the people affected. Instead, we use the reflexive pronoun "se" as a kind of "indefinite subject" with a singular verb. It ends up meaning something like, "someone did it". Notice also that we use the preposition "a" to indicate the human direct object.

• Se salvó a la víctima.
  The victim was saved.
• Se salvó a las víctimas.
  The victims were saved.

It would be possible to use a normal reflexive construction also, but the meaning would be changed.

• Se salvó la víctima.(without the preposition "a")
• Se salvaron las víctimas.(plural verb and no preposition "a")

In these sentences, the idea is different. Instead of meaning that the victims were saved by somebody, they suggest that somehow the victims saved themselves, by their own effort.