Passive voice - 2

The use
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 the passive voice is more polite than the 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.).

The examples

Tense   Subject Verbs (prepositional) Object
Simple Present Active: Rita writes a letter
  Passive: A letter is written by Rita
Simple Past Active: Rita wrote a letter
  Passive: A letter was written by Rita
Present Perfect Active: Rita has written a letter
  Passive: A letter has been written by Rita
Future Active: Rita will write a letter
  Passive: A letter will be written by Rita
Auxiliary verbs Active: Rita can write a letter
  Passive: A letter can be written by Rita