The category of voice reflects the objective relations between the action itself and the subject or object of the action. The category of voice is realized through the opposition Active voice::Passive voice. The passive is marked both in meaning and in form and the active as unmarked both in meaning and in form.
The realization of the voice category is restricted because of the implicit grammatical meaning of transitivity/intransitivity.
Some scholars admit the existence of Middle, Reflexive and Reciprocal voices.