I used to reach for the line myself: “We’re basically Orthodox in communion with Rome.” It’s an easy way to explain Byzantine Catholicism in one breath, and for a long time I didn’t know enough about actual Orthodox viewpoints and history to see what was wrong with it. I do now, and I think the line undersells what’s different.

The short answer: not quite. Communion with Rome is real and it matters, but treating it as the only variable assumes “Orthodox” names one fixed, unchanging thing that we’re simply Orthodox-plus-one-difference from. It doesn’t. Orthodoxy itself went through a real historical reorientation — not in its core dogma, but in its posture — and Byzantine Catholics never had to go through it.

What the shorthand gets right

Byzantine Catholics and the Eastern Orthodox share almost everything that shows up when you walk into a church: the same Divine Liturgy, icons, chant, fasting calendar, married priesthood, monastic tradition, the same theology of theosis — becoming by grace what God is by nature. Up until the point our histories diverge, we’re reading the same Fathers and singing the same troparia. What Is the Byzantine Catholic Church? puts the visible difference honestly: “The difference is communion with Rome.” True at the level of the big picture. The real difference is in the details.

1453, and a tradition forced to reorient

Before the Unions tells part of this story: in 1439 the Council of Florence healed the Great Schism on paper, with the Byzantine Emperor and the leading Eastern clergy signing on — a union real enough that a unionist liturgy was celebrated at the Hagia Sophia in December 1452. Five months later, Constantinople fell to the Ottomans.

What happened next is the part the shorthand skips over. The eastern theologians who’d championed the union and could escape did, many into Italy, where Greek scholarship — already trickling west since Manuel Chrysoloras began teaching in Florence in 1397 — now arrived in force.

An example of this is Cardinal Bessarion — a native Greek, born in Trebizond (modern-day Turkey) and educated in Constantinople — who became one of the great patrons of Greek learning in the West, helping fuel the Renaissance’s recovery of classical antiquity. Those who stayed had no such freedom: the Ottomans had every reason to prevent a unified religious front with Catholic Europe, so the patriarchs they allowed to be appointed were reliably anti-union. Mark of Ephesus — the one bishop at Florence who’d refused to sign — went in a single generation from isolated vocal dissenter to the patron saint of the position that would define Orthodoxy from then on.

That reorientation kept unfolding for centuries. Cut off from Constantinople’s old imperial and intellectual establishment, Orthodox theological life drifted toward the monasteries and away from Ottoman-dominated city centers — Mount Athos above all, always the tradition’s most ascetic, most conservative wing. It reached one of its clearest expressions in 1782, when two Athonite monks published the Philokalia in Venice, the anthology that anchored a monastic revival built on strict fidelity to inherited practice and real suspicion of anything that looked like a Western innovation.

None of this created a new doctrine. The old dividing lines were centuries older than 1453, and Florence had already addressed the sharpest of them, the Filioque: the council defined that the Holy Spirit proceeds eternally from the Father and the Son as from one principle, and that the Eastern Fathers’ “through the Son” carries the same meaning as the Latin “and the Son.” It was a conciliatory definition the Eastern delegation signed, and it’s the one Byzantine Catholics hold today. What changed after 1453 was disposition: a felt need to define the tradition by its distance from the West, because under occupation that distance had become existentially important.

A live example: “the pan-heresy of ecumenism”

This isn’t buried history. In 2016 the Ecumenical Patriarchate convened the first Pan-Orthodox Council in over a millennium. Several Athonite monasteries objected to its draft documents beforehand, and a few weeks after the council more than sixty Athonite monks, led by Elder Gabriel of Koutloumousiou, signed an open letter urging the abbots to reject it and saying they would stop commemorating the Ecumenical Patriarch. Their charge: that the council had given “the pan-heresy of ecumenism” a green light — treating dialogue itself as a betrayal on par with the ancient heresies. That phrase is a direct descendant of the reorientation that started in 1453.

To be fair, this is one influential strand, not all of Orthodoxy — the Ecumenical Patriarchate itself has pursued formal dialogue with Rome for decades, and plenty of Orthodox bishops and theologians take ecumenism seriously. Even Athos’s own governing body answered that letter by asking for revisions to the council’s texts, not their rejection. The zealot wing is loudest on Mount Athos and among the Old Calendarist splinters. But it’s real, it’s influential, and it’s a development of the last several centuries — not something Byzantine Catholics ever had reason to develop ourselves.

What we kept instead: unity

Byzantine Catholics carry the same inheritance — the icons, the fasts, the married priesthood, the monasteries. That part of the shorthand is correct. But because communion with Rome was never permanently severed for us, or was restored through unions like Florence’s Ruthenian aftermath, Brest, and Uzhorod, we never needed a theological identity defined against the West. That’s why ecumenism was never a dirty word for us. Sharing one faith across different rites, patriarchs, and languages was never a threat to manage — it’s the ordinary condition of the Catholic Church’s twenty-four sui iuris churches, and it was already the condition of the Church at Pentecost, when the crowd marveled to hear the apostles preach, “each one heard them speaking in his own language” (Acts 2:6).

The main difference, then, isn’t another doctrine but a disposition. Our instinct is a more conciliatory, academically minded approach rather than a reactionary and divisive one — and from the Catholic Church’s own perspective, many of the divisive issues were never actually condemned. Many of the differences in views, once distilled, come down to the same definitive truth, as the Florentine definition of the Filioque shows. What God Is, and What God Is Not touches on another example: the essence-and-energies distinction, and how much more at home it is in a Western viewpoint than the usual East-vs-West framing admits. We’ll be the first to tease our Latin brothers and sisters about their legalism, but we’ll also be the first to explain that, despite the East-West differences, you can arrive at the same truth the whole Church holds.

So — are Byzantine Catholics just Orthodox in communion with Rome?

Structurally, sort of. But that phrasing assumes Orthodoxy is the fixed reference point and we’re the variant, when it’s closer to the opposite: both traditions carry the same ancient inheritance, and one of them spent centuries under real duress learning to define itself against the other half of a Church it used to share. We didn’t have to learn that lesson.

“That they may all be one” (John 17:21) was Christ’s own prayer the night before he died. We don’t treat it as a threat to manage. We treat it as already, however imperfectly, ours to live.