Passive voice is used when the focus is on the action. It is not important or not known, however, who or what is performing the action.

Example: My bike was stolen.

In the example above, the focus is on the fact that my bike was stolen. I do not know, however, who did it.

Sometimes a statement in passive is more polite than active voice, as the following example shows:

Example: A mistake was made.

In this case, I focus on the fact that a mistake was made, but I do not blame anyone (e.g. You have made a mistake.).


Subject + finite form of to be + Past Participle (3rd column of irregular verbs)

Example: A letter was written.