1. When the actor (the person or thing
doing the action of
the verb) is redundant (i.e., easy to supply and therefore not expressed).
Grapes are grown in California. (The
actor here is "vintners," which is not necessary.)
*
2. When the writer wants to emphasize the receiver or result of the
action.
Six people were killer in the fire. (As opposed to: The fire killed six people).
*
3. When the writer wants to be tactful or evasive by not mentioning
the agent.
Kristin was given some bad advice. (As
opposed to: David gave Kristin some bad advice.)
*
4. When the writer wants to make a statement sound more objective without
revealing the source of the information.
It is believed that she will announce her resignation
today.
*
5. When the writer wants to retain the same grammatical subject in successive
clauses, even thought the function of the noun changes form.
Kristin finished her paper, but she was exhausted
by the task.
*
6. When the passive is more appropriate than the active (usually non-complex
sentences).
ACTIVE: The results of this second language learning experiment tend
to confirm the hypothesis, as Bogen, Paivio, Cohen and Witkin suggest,
that students learn in different ways.
PASSIVE: The results of this second language learning
experiment tend to confirm the hypothesis that students learn in different
ways as suggested by Bogen, Paivio, Cohen and Witkin.
*
7. When the theme is given information and the agent is new information.
What a lovely tie! Thank you. It was given to
me by Kristin.
Passives can change the meaning of a sentence, so one should be careful
when using them. Here are the classic examples:
Everyone in the room speaks two languages. (i.e., any two languages
per person)
Two languages are spoken by everyone in the room.
(i.e. two specific languages that everyone speaks.)
Few people read many books. (i.e., there are few people who read lots
of books.)
Many books are read by few people. (there
are many books that are read by few people.)