Differences between Active and Middle.—As contrasted with the active, the middle lays stress on the conscious activity, bodily or mental participation, of the agent.
In verbs that possess both active and middle: βουλεύεσθαι
a. Many such verbs form their futures from the middle: ἀκούσομαι, ᾄσομαι, ἁμαρτήσομαι. See cross805.
b. In verbs in -ευω, the middle signifies that the subject is acting in a manner appropriate to his state or condition: πολι_τεύειν
a citizen, perform one's civic duties; πρεσβεύειν
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].