Active voice means that the subject of the sentence is doing the action. Passive voice means that the object of the sentence behind a preposition, even if no prepositional phrase is present, is doing the action.
Example: I threw the ball (active).
Example: The ball was thrown by me (passive).
Example: The package has been sent (passive, no object).
To recognize passive voice, use three clues.
- Check if the subject is doing the action.
- Check the verb. Passive voice verbs require a helping verb and the 3rd form of a verb.
- Check the object of the preposition. If the object after "by" or "to" is actually doing the action of the sentence, then the sentence is passive.
For clarity and efficiency, stay in active voice as much as possible. To change a sentence to active, make the actor the subject, simplify the verb, and make the receiver the object.
Example: The word pairs were read to the learner by the scientist (passive, 11 words).
Example: The scientist read the word pairs to the learner (active, 9 words).
Passive voice is acceptable when the actor is unknown.
Example: The building was renovated in 2001 (We do not know who did the renovation).
Passive voice is acceptable in scientific writing to avoid 1st person.
Example: The experiment was run four times ("I" ran the experiment).