Active Verbs with Aorist Passive in a Middle Sense.—The aorist passive of some active verbs has a reflexive or middle sense, either sometimes or always. Thus εὐφραίνω
a. These verbs are often called
b. The middle and the passive form of the future of such verbs is often found, the middle being frequently preferred.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].