Converting from active to passive
What you'll need:
- one active clause with
- a real subject1
- an object (lexically rendered, if applicable)
Sample active clause:
The poor girls' parents marry them off at a young age.
The poor girls are married off by their parents at a young age.
Alternately, you can omit the new Object, the Circumstance, or both, if you wish to change the information conveyed in the new sentence:
The poor girls are married off at a young age.
The parents are not longer portrayed as the agents of the verb.
The poor girls are married off.
The age of the girls are no longer conveyed.
The poor girls are married off by their parents.
The parents are still the age, but their age is no longer conveyed.
An interesting case: ditransitive verbs
I read him the book (present tense)
- Subject: I
- Object1 (indirect): (to) him
- Object2 (direct): the book
- Verb: read
He was read the book (by me).
The book was read to him (by me).
The book was read (by me).
In the case of ditransitive clauses, the direct object must be present in the passive clause:
He was read by me.
While this is technically grammatical, it doesn't have the same meaning as the Active clause, as the Active clause would now be:
I read him.
Converting from passive to active
The same thing, but in reverse:
- The verb is restored to the tense that be is in
- Remove the form of be adjacent to the verb
- The Object becomes the new Subject
- The Subject becomes the new Object
Handling cases where there is no Object in the passive
Of course, you can omit most Objects in the passive, with the exception for ditransitive verbs outlined above.
He was read the book.
Unfortunately, without more context, you can't recover the original Subject. This is a case where the writer/speaker, has (deliberately or not) omitted the original Subject (the Agent). This can be done for many reasons, for instance to lie by omission, or in the case where the person is unaware of the Agent.
Why convert to passive?
There are many reasons to convert to passive:
- You don't know what/who the agent/Subject was in the active: you can omit it in the passive.
- You don't want to say what/who the agent/Subject was in the active: you can omit it in the passive.
- You want to foreground/emphasise one of the Objects rather than the Subject.
- You want to background/underplay the Subject/agent
In fact, linguistically, the process of changing the grammatical roles from
Subject to Object and Object to Subject is called demotion and promotion,
1 I say a real subject, because relational, existential, and meteorological clauses, which technically have subjects can't be passivised.
- He is the Pope.
- It is raining.
- There is a dog.
- The Pope is/was him/he.
- Raining is/was it.
- A dog is/was there.
While The Pope is him/he is grammatical, it isn't really passivisation.
Interestingly, putting attributive clauses into the past tense can give them a passive-like construction.
This is a much larger can of worms, and it depends largely on the context as to whether it is a passivised clause or just an adjectival usage.