Read the following sentences:
1. The boy killed the spider.
2. The spider was killed by the boy.
As you can probably see both sentences express the same idea. In sentence 1, the form of the verb indicates that the person denoted by the subject (the boy) is the doer of the action.
The verb killed is therefore said to be in the active voice.
In sentence 2, the form of the verb shows that something is done to the person denoted by the subject (the spider).
The verb is killed is therefore said to be in the passive voice.
A verb is in the active voice when its form indicates that the person or thing denoted by the subject does something.
A verb is in the passive voice when its form indicates that something is done to the person or thing denoted by the subject.
In the following sentences, note the changes when an active sentence is converted into the passive.
1. John loves Alice. (Active)
2. Alice is loved by John. (Passive)
3. The masons are building the house. (Active)
4. The house is being built by the masons. (Passive)
5. Who did this? (Active)
6. By whom was this done? (Passive)
You will have noticed that when the verb is changed from the active voice to the passive voice, the object of the transitive verb in the active voice becomes the subject of the verb in the passive voice.
In sentence 1, John is the subject of the active verb loves. In sentence 2, Alice is the subject of the passive verb is loved.
Only transitive verbs can be used in the passive voice. Intransitive verbs cannot be used in the passive voice because they do not have objects.