We use passive voice when the focus of our sentence is on the action. This voice is ideal if we don't know who (or what) is performing the action, or think it is not important.
- My wallet was stolen.
In the above example, we are focusing on the fact that the wallet was stolen. We do not know who did it.
Subject + correct form of to be + past participle
Active to Passive?
- Mark told a funny story. active
- A funny story was told by Mark. passive
If you want to change the sentence's voice from active to passive, do the following:
- Move the active sentence's object ("A funny story") into the sentence's subject position.
- Create a phrase with the active sentence's subject ("Mark") and the preposition by.
- Add a correct form of auxiliary verb be to the main verb, and change its form to past participle.