The active voice is used when the agent (i.e, the doer of the action) is to be made prominent. The passive voice is used when the person or thing acted upon is to be made prominent. The passive voice is therefore preferred when the doer of the action is an indefinite pronoun or noun (e.g. somebody, anybody, they, people, we etc.)
- My watch has been stolen. (Passive)
- Somebody has stolen my watch. (Active)
In the example given above the passive structure is preferred because we don’t know who performed the action.
Compare:
- Peter has stolen my watch. (More natural than ‘My watch has been stolen by Peter.)
Here the emphasis is on Peter and therefore we use the active form.
In the following cases, the passive forms are preferred because the subject is vague or indefinite.
- I was asked my name. (Passive)
- They asked me my name. (Active)
- I was told to pay the fine. (Passive)
- They told me to pay the fine. (Active)
- English is spoken all over the world. (Passive)
- People all over the world speak English. (Active)
In passive clauses, we usually use a phrase beginning with by if we want to mention the agent – the person or thing that does the action.
- I was shocked by his arrogant attitude. (Passive)
- His arrogant attitude shocked me. (Active)
- The spider was killed by John. (Passive)
- John killed the spider. (Active)
Note that the agent is mentioned in only about 20% of passive clauses.