The grammatical category of voice.
The category of voice expresses the relation between the subject and the object of the action. This definition is more correct because not every sentence can have an object but the definition is more general.
Is invited was invited
Will invite will be inviting
Is invited is being invited
The passive construction is used when we do not know of it is unknown.
Pr. Allen counted the usage of passive constructions only 30 pr cent are used by phrase.
The active forms have wider range of distribution because it includes intransitive verbs then the verbs of have type. Some scholars speak not only active and passive but the other voices. The reflexive voice: he dressed himself
Reciprocal voice: They greeted each other
The middle voice: The door open. The letter reads.
Conclusion: We must disapprove the existence of these voices. All the ways of the expressions are not morphological.