Use the passive when (a) you don't know who/what the subject is or (b) you want to emphasize the verb's object. With active sentences, the object always comes third, or there abouts:
Subject+Verb+Object: Max hit Pat.
With passive sentencs, the object comes first,
Object+Verb (+Subject): Pat was hit (by Max).
The subject (i.e., Max) is usually not stated. In fact, if the subject is more important than the object, then the active structure should be used. If the subject is not important however then the passive is used.
My car was hit! (by someone or something. I don't know who or what hit it. Even if I knew who hit it or what hit it, I would still use the passive because I want to place focus on the object of the verb 'hit', 'My car'.
Someone hit my car. (Active)
My car was hit. (Passive)
While it is very important to me that I find out the someone or the something that damaged my car, the most important thing at this very moment is my car, so I use the passive to emphasize that by placing the verb's object ('my car') at the head of the sentence, which is the most prominent position in the sentence; Now 'My car' are the first words people will hear.
The universe was created billions of years ago. (Who created the universe? I don't know. Do you? Use the passive.)
The problem isn't being dealt with. (The important thing here is the problem. The person who isn't dealing with the problem is of no importance to me. By using the passive, I can take focus of the person and place focus on the problem.)
The building was erected in 1942. (The company that erected the building is of no importance to me. I use the passive to emphasize the biulding, which in an active sentence would come third and moreover would require a subject:
Smith Construction erected the building in 1942. (Active)
I don't care about Smith Construction, and I don't want my audience to care about Smith Construction, so I use the passive to get rid of the subject:
The building was erected in 1942. (Passive)
If I want to make a passing remark about the true subject, I will add a by phrase, like this,
The building was erected in 1942 by Smith Construction.
Note, A passive sentence has two subjects: The building is called the grammatical subject, or subject, whereas whatever comes after 'by' (i.e., Smith Construction) is called the semantic subject.
Active: Max (subject) hit Pat (object).
Passive: Pat (subject) was hit by Max (semantic subject).
In short, with passive sentences, the verb's object graduates to a subject, and the subject is demoted: it's either omitted or attached to a 'by' phrase as a passing remark.
- For Teachers