Hello all,
I've been meaning to revisit this question for many months now, and perhaps get a better understanding than I did when I first learned of it.
I'd like to especially invite OO members who might be able to help me understand, and I'm sure I could use the help of fellow EO who understand better than I, as well as anyone else who has an understanding of the issues.
I'm not sure there are any active OO members on this website other than me, sadly. ArmenianJohn mainly posts in other areas, wgw has gone EO (though I imagine he can still give accurate representation of our theology and Christology; Syriac Orthodox have a lot closer relationships to the EO counterpart Antiochians than Copts tend to, so it's less of a dramatic switch in that case), Shanethetheologian is now Anglican, etc.
I hope the water isn't deeper than I'm able to navigate. I think it may come down to nuances in the Greek???
Not that I've noticed. Our fathers such as St. Athanasius the Apostolic, St. Cyril, St. Severus, etc. all wrote in Greek, and Greek is a perfectly fine language in which to express OO theology and Christology. Even today something like ~10% of hymns in the Coptic Orthodox liturgy are Greek (in addition to virtually all the deacons' responses), though I suppose Egyptians have a funny way of pronouncing it.
But the disagreement is primarily in the "two natures of Christ", which EO would claim, and define as being fully God, fully man, not mixed or confused.
Yes, and that disagreement has its roots in the preexisting philosophical traditions embraced and propagated by Alexandria vis-a-vis Antioch, not in which language is used. It would probably help you to review the one-time conflict between St. Cyril of Alexandria and John of Antioch, if mostly to see one real-world, pre-Chalcedon example of conflict between the miaphysites (represented by St. Cyril's party) and the dyophysites (represented by John's party), and more importantly how it was resolved. This would hopefully help make clear how and why we came to be different communions, especially by contrasting the formula of reunion embraced then to the Henotikon of Zeno (482), the creation and propagation of monothelitism as a supposed compromise (which the OO as a communion never accepted, just by the way; in fact, this is theorized by some historians such as Matti Moosa to have been the origin of the Maronites, whose liturgical patrimony points to Syriac Orthodox roots but eventual embrace of monothelitism placed them outside of both OO and EO, theologically), and so on. There is a very brief summary of the 433 Formula of Reunion from the Coptic perspective on the L.A. archdiocese's website, if you are interested in it:
http://lacopts.org/story/saint-cyril-of-alexandria-and-the-council-of-ephesus/
Some EO who did not know better have claimed on this very website that we do not accept this, or think of it as coerced or what have you, but as you can read from the above link, we very much accept the reunion of the Antiochians and the Alexandrians. At the same time, we recognize that this is not the same reunion that we could potentially have today with OO and EO, since neither party is exactly the same as it would have been in 433...yes, primarily due to one subsequent council...I bet you can guess which one it is...
Philosophically speaking, there are to some extent differing emphases in our respective treatments and understandings of the incarnation. EO user Rakovsky and I got into it for some pages many a thread ago concerning this, with him offering up excerpts from St. Cyril's letters that he felt supported the dyophysite position, and me doing the same from the same letters for the miaphysite position. Since both are supportable (I'm not going to say equally supportable, but y'know...supportable) from the same source materials, I'd prefer to think of it as a difference in emphasis, though no doubt EO would have their own view regarding why only their interpretation of things is correct (as they seem to regarding everything else concerning those matters in which we differ, as is to be expected).
So how exactly would my OO brothers answer this, please?
'This' what? Why we differ? Why we're not one communion anymore? I'm not sure what you're asking.
We differ because of differing traditions and understandings regarding the incarnation and what it means concerning the nature of Christ. As to why we're not one communion anymore, it would be hard to be so after so many centuries of developing separately, and you guys developed far more than we ever have, so there's a lot of stuff that you do and a lot of controversies that you were involved in that frankly do not matter to us, as is the case with, e.g., the issues surrounding the EO-RC 'Great Schism', since we were out of the picture for about five centuries by that point. (We were telling the bishop of Rome to go take a flying leap before it was cool.

)
Also, by the time of Chalcedon, there was no longer room for the earlier approach taken by our common father St. Cyril in his letter to John of Antioch (letter 39), wherein our father points out "
For one is the Lord Jesus Christ, although the difference of his natures is not unknown, from which we say the ineffable union was made". By Chalcedon, it was clearly not enough to say that He is both perfect God and perfect Man, as we all do say (since we are
miaphysites, after the formula of St. Cyril, not
monophysites); rather, our teacher St. Dioscorus was told explicitly that unless he said "two natures" as the dyophysites all did, he would be deposed! Thankfully he did not do so, as you will note that in the same letter (
available here), HH St. Cyril discusses the humanity and the divinity at length, and while also explicitly referring to the
nature, not natures, of the Word of God (as you'd expect from the author of That Christ is One/On the Oneness of Christ, no?):
"
But I am far from any such thought as that, and I also consider them wholly to rave who think a shadow of change could occur concerning the Nature of the Word of God"
As surely inadequate as it is, I hope that this post gives you something to think about and research, and I welcome further exposition and/or clarifications from any fellow OO concerning our own position, and any questions from EO. I figure it best to start with a common father like HH St. Cyril, rather than quoting people who are more cross-communally controversial, such as HH St. Severus, HH St. Timothy, etc.