The article suggests that the verb-forms in the sentences: “The door opened. The book sells well”, should be treated as the forms of the implicit category of the Middle Voice in Modern English. It is related to the category of transitivity/intransitivity of English verbs in particular and Indo-European verbs in general. The communicative aspect of this grammatical phenomenon is expressed by the growing number of transitive English verbs being used as intransitive.
Keywords: category of voice, middle voice, transitivity/intransitivity of English verbs.