When is a θη Form not Passive?

¶ I don't think this is a good example to illustrate your point, since even you acknowledge that the semantics of the particular verb, in this case, allows one to think of it in different ways that all work. If active, then they gather together; if middle, then they gather together such as to be gathered together (i.e. gather themselves together); if passive, they are gathered together (by an unspecified causal agent). ¶ I would be interested in seeing a different example "θη" form where the active vs. middle vs. passive meanings were distinct and semantically contrasting. ¶ Also, συνηχθησαν is the verb form of synagogue. Obviously, that has become a religious word in English ("Jewish church"), which also does not have a corresponding verb form in English, but that was "church" to them, and you could ask the same question that people in Christian circles ask today: "What is 'church'?" In our case, εκκλησια is out-calling (we gather because we are out-called but, fundamentally, we are the "out-called," the "church"). The way this relates to Matt 26:3 is that συνηχθησαν is more official and formal than, say, if it was said that they συνηλθον ("come together"), which would just express the mechanics of it. The point would be that they "synagogue" (themselves) together (but without the modern, religious meaning of "synagogue"). So, again, active vs. middle vs. passive is murky in that case.