Active and passive
A What is the sentence about?
Compare these two entries in an encyclopedia.
Alexander Graham Bell: A British inventor who went to live in Canada and then the USA. Bell invented the telephone.
Telephone: An apparatus with which people can talk to each other over long distances. The telephone was invented by Alexander Graham Bell.
Look at these two sentences.
ACTIVE PASSIVE
Bell invented the telephone. The telephone was invented by Bell.
The two sentences have the same meaning, but they are about different things. One sentence is about Bell, and the other is about the telephone. Each sentence begins with the subject. The subject is the starting-point of the sentence, the thing we are talking about. The new information about the subject comes at the end of the sentence.
We say Bell invented the telephone because we are talking about Bell, and the new information is that he invented the telephone. When the subject is the person or thing doing the action (the agent), then we use an active verb.
We say The telephone was invented by Bell because we are talking about the telephone, and the new information is that it was invented by Bell. When the subject is not the agent (is not doing the action), then we use a passive verb.
B The passive and by the police, in 1876, etc
In a passive sentence, when we want to say who or what did the action, we use by.
On our way home we were stopped by the police.
The new hospital will be opened by the Queen.
The paper was all blown away by the wind.
We can give other details about the action. For example, we can use a phrase saying when or where something happens.
The telephone was invented in 1876.
The visitors will be driven to the airport.
The concerts are usually held at the university.
Sometimes there is no phrase after the verb.
A new swimming-pool is being built.
All the documents have been destroyed.
C The passive and the agent
In a passive sentence, we sometimes mention the agent (the person or thing doing the action). We use by with the agent.
The cheque must be signed by the manager.
The medals were presented by Nelson Mandela.
But we mention the agent only if it is important for the meaning of the sentence.
Sometimes we do not mention the agent.
1 We do not mention the agent if it does not add any new information.
All our money and passports were stolen.
A man was arrested last night.
We do not need to say that the money was stolen 'by a thief' or that the man was arrested 'by the police'.
2 We do not mention the agent if it is not important.
The streets are cleaned every day.
Oil has been discovered at the North Pole.
Who discovered the oil is less important than the fact that it is there.
3 It is sometimes difficult to say who the agent is.
This kind of jacket is considered very fashionable these days.
A number of attempts have been made to find the Loch Ness monster.
D Empty subjects (they, people, etc)
Compare these two sentences.
ACTIVE PASSIVE
They clean the streets every day. The streets are cleaned every day.
The new and important information is how often the streets are cleaned. We are not interested in saying who cleans them. In the active sentence we can use the 'empty subject' they. We sometimes use a sentence with an empty subject instead of the passive, especially in conversation.
We can also use the empty subjects people, you, one and someone.
ACTIVE PASSIVE
People use this footpath all the time. This footpath is used all the time.
You/One should check the details. The details should be checked.
Someone took my purse. My purse was taken.
E When do we use the passive?
We use the passive in both speech and writing, but it is more common in writing. We see it especially in textbooks and reports. We use it to describe activities in industry, science and technology, and also for official rules.
Bananas are exported to Europe.
The liquid is heated to boiling point.
Payment can be made at any post office.
Cars left here will be towed away.
In these situations, it is often not important to say who is doing the action, or it is difficult to say.
The passive is also often used in news reports.
A number of political prisoners have been released.
Talks will be held in London next week.