To summarize, all markedness-criteria point in the same direction: the active voice is the unmarked member in the opposition with the marked middle voice. Since the active voice can occur in environments in which the subject is affected (contextual neutralization), it can be concluded that the active is unspecified as to the semantic feature subject-affectedness. Conversely, the middle voice is semantically marked with respect to affectedness of the subject. As a consequence, event types that do not involve subject-affectedness cannot be expressed by a middle verb. The two major event types that do not involve subject-affectednesss are the prototypical transitive and the stative event type. In the prototypical transitive event, the subject is an unaffected volitional agent, while the object is the sole participant undergoing the effect of the event. In stative events there is no affectedness, since affectedness can only be the result of a change that is taking place or has taken place.
Allan, Rutger. The Middle Voice in Ancient Greek: A Study in Polysemy. Amsterdam: J.C. Gieben, 2003. 29.