passive voice

Use of Passive

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.).

Form of Passive

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

Example: A letter was written.

When rewriting active sentences in passive voice, note the following:

• the object of the active sentence becomes the subject of the passive sentence
• the finite form of the verb is changed (to be + past participle)
• the subject of the active sentence becomes the object of the passive sentence (or is dropped)

Examples of Passive 

Tense		Subject	Verb	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 I	Active:	Rita	will write	a letter.
	Passive:	A letter	will be written	by Rita.
Hilfsverben	Active:	Rita	can write	a letter.
	Passive:	A letter	can be written	by Rita.

Examples of Passive 

Tense		Subject	Verb	Object
Present Progressive	Active:	Rita	is writing	a letter.
	Passive:	A letter	is being written	by Rita.
Past Progressive	Active:	Rita	was writing	a letter.
	Passive:	A letter	was being written	by Rita.
Past Perfect	Active:	Rita	had written	a letter.
	Passive:	A letter	had been written	by Rita.
Future II	Active:	Rita	will have written	a letter.
	Passive:	A letter	will have been written	by Rita.
Conditional I	Active:	Rita	would write	a letter.
	Passive:	A letter	would be written	by Rita.
Conditional II	Active:	Rita	would have written	a letter.
	Passive:	A letter	would have been written	by Rita.

Passive Sentences with Two Objects 

Rewriting an active sentence with two objects in passive voice means that one of the two objects becomes the subject, the other one remains an object. Which object to transform into a subject depends on what you want to put the focus on.

	Subject	Verb	Object 1	Object 2
Active:	Rita	wrote	a letter	to me.
Passive:	A letter	was written	to me	by Rita.
Passive:	I	was written	a letter	by Rita.

sumber:http://www.ego4u.com/en/cram-up/grammar/passive