What follow is a compilation of quotes from Robertson discussing the problems & challenges in distinguishing middle & passive voice:
As is well known in Homer, the future passive forms do not occur except two, μιγήσεσθαι and δαήσεαι (Stahl, Syntax, p. 66), and the distinction between aorist middle and aorist passive is indistinct. Indeed, strictly speaking, there was no passive voice as to form in Greek, as there was none in the original Indo-Germanic speech.
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With Intransitive or Transitive Verbs. “Theoretically the passive ought to be formed from transitive verbs only with an accusative object.” But Greek follows no such narrow rule. That is an artificial rule of the Latin which Greek knows nothing about.
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Transitive passives are usually verbs that in the active have two accusatives or an accusative of the thing with the person in the dative or ablative. This accusative of the thing is retained in the passive.
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The transitive passive “deponents,” like μὴ φοβηθῆτε αὐτούς (Mt. 10:26), call for special discussion a little later. Certainly there is no “passive” sense in πορευθῆναι
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In ἁγνίσθητι (Ac. 21:24) the passive apparently has the force of ‘let’ or ‘get’ (cf. the causative middle). Cf. also περιτέμνησθε (Gal. 5:2).2 It is possible so to regard ἀδικεῖσθε and ἀποστερεῖσθε (1 Cor. 6:6 f.). Sometimes, indeed, it is difficult to tell whether a verb is middle or passive. Cf. πτωχοὶ εὐαγγελίζονται (Mt. 11:5), προεχόμεθα (Ro. 3:9), ἐνδυναμοῦσθε (Eph. 6:10). Indeed, as already said, in all the Greek tenses save the aorist and the future it is always an open question whether we have middle or passive.
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It is probable that ἠγέρθη sometimes (as in Mk. 16:6) is merely intransitive, not passive, in idea.
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The so-called passive “deponents,” verbs which had no active, formed the aorist with the passive form. But they were not always intransitive. Some of them were so, like πορεύομαι (Mt. 8:9), μεταμέλομαι (Mt. 27:3), δύναμαι (Mt. 17:16), but most of them are really transitive.
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As examples of the transitive passive deponents note ἐβουλήθη (Mt. 1:19), ἐδεήθη (Lu. 5:12), ἐνθυμηθέντος (Mt. 1:20), ἐπεμελήθη (Lu. 10:34), ἐφοβήθη (Mt. 14:5). These passive aorists have precisely the construction that the middle or active would have so far as case is concerned. The distinctive passive sense is absent. Some of the “deponents” have both a middle and a passive aorist with a distinct passive sense. Thus note the middle and passive voices side by side in ἀρνησάμενος and ἀπαρνηθήσεται(Lu. 12:9).
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As a result of this inroad of the comparatively new passive forms the aorist middle forms vanished. In modern Greek the passive aorist form is almost invariably used for both the middle and the passive ideas. This tendency seen in the N. T. (and the rest of the κοινή) has triumphed over the aorist middle. In Ro. 10:3, τῇ δικαιοσύνῃ τοῦ θεοῦ οὐχ ὑπετάγησαν, the Rev. V. translates ‘they did not subject themselves to the righteousness of God.’
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It is quite within bounds, therefore, to speak of “medio-passives” in the future as in the aorist. The idiom appears in the papyri. So narrow is the dividing-line between middle and passive (Robertson, 815-819).
One question that we can ask in the context of these quotations is this: Beyond simply making it “easier” for beginning students (most of whom wouldn’t know what active voice was if it hit them in the face anyway), what is the point of so explicitly and absolutely separating these categories (passive and middle) when there is effectively no basis for such a division in the language itself?
The Greek voice system does not need to be forced into an English active-passive format. We can let Greek voice be Greek, let it be itself.
Cited:
Robertson, A. T. 1923. A Grammar of the Greek New Testament in the Light of Historical Research. London: Hodder & Stoughton.
Koine-Greek 