Transitive and Intransitive Verbs
When a verb is transitive, the sentence describes an action received by a 'direct object'. For example,
In these examples, the subject performs the action received by the object, and we therefore say that the transitive verb is in the active voice. We can change transitive verbs in the active voice to transitive verbs in the passive voice by making the receiver of the action (the object when voice is active) the grammatical subject of the sentence.
Note how the performer of the action is the grammatical subject in the active voice sentence and is the object of a prepositional phrase or is absent in the passive voice sentence. Also note that the passive voice form of the transitive verb requires an auxilliary (= helper) verb.
When a verb is intransitive, the sentence describes an action not received by an object.
These intransitive sentences lack direct objects. Instead they usually have prepositional phrases. Prepositional phrases have objects, but these phrase objects do not receive actions in the manner of direct objects.