Pope St. Leo II anathematizes Honorius for permitting the Monothelite heresy, while the inventors of the error are not explicitly called heretics in the same formula, since the dogmatic Sixth Ecuмenical Council had already condemned and anathematized them as heretics:
“To Honorius, the heretic, anathema!“
In Session XVI of the Sixth Ecuмenical Council (680–681), Honorius I was formally labeled a “heretic”, alongside other Monothelite leaders, yet he remained pope until his death. The council’s acclamation reads verbatim:
“To Theodore of Pharan, the heretic, anathema!
To Sergius, the heretic, anathema!
To Cyrus, the heretic, anathema!
To Honorius, the heretic, anathema!
To Pyrrhus, the heretic, anathema!
To Paul, the heretic, anathema!
To Peter, the heretic, anathema!
To Macarius, the heretic, anathema!
To Stephen, the heretic, anathema!
To Polychronius, the heretic, anathema!
To Apergius of Perga, the heretic, anathema!
To all heretics, anathema!
To all who side with heretics, anathema!”
— Nicene and Post‑Nicene Fathers, Second Series, Vol. XIV: The Sixth Ecuмenical Council, Session XVI
The council language itself used the word “heretic” in association with his name.
The dogmatic decree itself (as recorded in Mansi, Sacrorum Conciliorum, Tomus XI, cols. 635‑637) also states:
“…Honorius, qui fuit Papa antiquae Romae… haeretico anathema…”
English: “…Honorius, who was Pope of Old Rome… anathema to the heretic…”
The Council repeatedly identified Honorius as a heretic, both in the acclamations of the bishops and in the formal dogmatic decree.
Notice in Pope St. Leo II’s own words:
“And in like manner we anathematize the inventors of the new error, that is, Theodore, Bishop of Pharan, Cyrus of Alexandria, Sergius, Pyrrhus, Paul, and Peter, betrayers rather than leaders of the Church of Constantinople, and also Honorius…”
Those people were using the word "heretic" in a way that is not defined by the Church. The Church provides the definition in Canon Law. What Leo II describes Honorius as doing does not meet the criterion of what the Church call heresy today. And that definition has been in place for quite a while.
We must use terminology the way that the Church authorizes it. And Pope Leo II, in his declaration, did not call Honorius a "heretic." He simply described what he failed to do and anathematized him for his failures. You will notice that
failures in governance do not fit the definition of "heresy," which you will find in bold below.
Canon 1325 (1983 CIC 209, 751, 755)
§ 1. The faithful of Christ are bound to profess their faith whenever their silence, evasiveness,
or manner of acting encompasses an implied denial of the faith, contempt for religion, injury to
God, or scandal for a neighbor.
§ 2.
After the reception of baptism, if anyone, retaining the name Christian, pertinaciouslydenies or doubts something to be believed from the truth of divine and Catholic faith, [such a oneis] a heretic; if he completely turns away from the Christian faith, [such a one is] an apostate; if
finally he refuses to be under the Supreme Pontiff or refuses communion with the members of the
Church subject to him, he is a schismatic.
§ 3. Let Catholics beware lest they have debates or conferences, especially public ones, with
non-Catholics without having come to the Holy See or, if the case is urgent, to the local Ordinary.