oxford_guide_to_english_grammar

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104 The use of the passive
There is no need to say that nine million cigarettes are smoked by smokers all over
the world, or that in America 10,000 crimes are committed by criminals. This is
already clear from the context. Here are some more examples.
A new government has been elected. The man was arrested.
'Hamlet' was written in 1601.
It is well known that 'Hamlet' was written by Shakespeare, so we do not need to
mention it. For the same reason, we do not need to say that the man was arrested
by police or the government elected by the people.
NOTE
We use the verb bear (a child) mainly in the passive and without an agent.
Charles Dickens was born in Portsea.
b
c
d
The agent may not be relevant to the message.
A large number of Sherlock Holmes films have been made.
The atom was regarded as solid until the electron was discovered in 1897.
The makers of the films and the discoverer of the electron are not relevant. The
sentences are about the number of films and the time of the discovery.
Sometimes we do not know the identity of the agent.
My car was stolen.
The phrase by a thief would add no information. But we can use an agent if there is
some information.
My car was stolen by two teenagers.
Sometimes we do not mention the agent because we do not want to.
Mistakes have been made.
This use of the passive without an agent is a way of not saying who is responsible.
Compare the active I/We have made mistakes.
4 Empty subjects
Even when the agent is not important or not known, we do not always use the
passive. Especially in informal speech, we can use you, one, we, they, people or
someone as vague and 'empty' subjects. But a passive sentence is preferred in
more formal English.
Active: You/One can't do anything about it.
Passive: Nothing can be done about it.
Active: We/People use electricity for all kinds of purposes.
Passive: Electricity is used for all kinds of purposes.
Active: They're building some new houses.
Passive: Some new houses are being built.
5 Typical contexts for the passive
We can use the passive in speech, but it is more common in writing, especially in
the impersonal style of textbooks and reports.
a
To describe industrial and scientific processes
The ore is usually dug out of the ground.
The paint is then pumped into a large tank, where it is thinned.
If sulphur is heated, a number of changes can be seen.