The category of voice expresses the relations between the subject and the object of the action. He invited his friends. – He was invited by his friends. In the first sentence he – is a doctor of the action, in the second – the object of the action.
The grammatical category of voice is represented by the opposition of active and passive voice. (invites – is invited; is inviting – is being invited; invited – was invited; has invited – has been invited; should invite – should be invited).
The passive form is a strong member of the opposition.
In colloquial speech the role of the passive auxiliary may be performed by get or become. The frequency of occurrence of the English Passive voice is very great, greater than in Russian. One of the reasons is that the number of verbs capable of forming the Passive voice (not only transitive but also intransitive including prepositional ones) is greater in English than in Russian.
The question is, whether there are other voices in the English verb, besides active and passive. At various times the following three voices have been suggested in addition:
the reflexive, as in He dressed himself.
the reciprocal, as in They greeted each other, and (возвратный)
the middle voice, as in The door opened.