Dr. Ed Feser gives a brief rundown of the “error” and condemnation of Pope Honorius I (625-638). He draws mostly from the Patristic scholarship of great Fr. John Chapman who was a remarkable scholar on the early Papacy and the issues related to the Latin vs Byzantine Churches throughout the first seven ecumenical Councils. In my own research, I have come to think that Fr. Chapman’s is perhaps the best sketch and explanation of the events surrounding Honorius. There can be no question that Pope St. Leo II, the very Pope who confirmed the decrees of the Council of Constantinople III (681), that is, the very council which had accused Pope Honorius of heresy, believed that his predecessor Honorius had committed a heresy. There can be no question that, including Constantinople III, three more ecumenical synods repeated the anathema against Honorius for heresy. Moreover, in the Roman Breviary, up until the 18th century, included a description of Honorius as a “heretic” for June 28th, the feast of the Pope who executed Honorius’s condemnation (St. Leo II). There also can be no question that these Councils, Popes, theologians, canonists, and general Christian thinkers understood Honorius as a heretic. Though, you have some exceptions.
One thing that Feser does not venture deeply into is the question of what kind of “heretical crime” was proven at the Council in 681 over Honorius, a man who had died 42 years prior to its convocation. At best, Honorius can be convicted of material heresy since the form added to the matter of heresy has to be proven. Moreover, since the doctrine of two-wills in Christ was not definitively settled, even a material heresy in this regard (according to Catholicism’s developed canon law) could not, of itself, situate one into the canonical crime of heresy nor the status of mortal sin. Otherwise, we would have to anathematize the person and memory of St Thomas Aquinas for his rejection of the Immaculate Conception. But that is impossible since Pope Sixtus condemned anyone who would accuse another for mortal sin or canonical heresy when the matter had not yet been resolved by the Apostolic See. While the Council of Constantinople III cannot be said to have worked with these parameters, those parameters did become standard and acceptable to Catholic canon law, jurisprudence, and pastoral theory. It is practical today.
What lessons, asks Feser, can be drawn from Honorius for us today? I think the most that can be drawn is that a Pope can commit a doctrinal error. But that a Pope could teach heresy and thereby become a formal heretic is not illustrated by the Honorius-event. One might argue that the Honorius-event lends great precedent that such a thing could, in theory, happen. But there is nothing in the Honorius-event, according to developed Catholic beliefs on the nature of heresy and its criminality, that illustrates that precedent. Now, if we revert back to the standards of the Latin and Greek policies during the 7th century, then it is a foregone conclusion, a Pope can become a formal heretic. But it seems to me that we cannot ignore the canonical, theological, and pastoral developments that have taken place since Honorius to the present day.
For a more relevant historical context wherein a Pope committed an error while in office, coupling form and matter (but perhaps not pertinacity), you would have to study the Three Chapters controversy under Emperor Justinian regarding the Constituta of Pope Vigilius.
PS. For the life of me, when I read Honorius’s letters, my own private judgment does not see him as a true Monothelite. His statements, as interpreted by his successor Pope John IV and St. Maximus the Confessor, seem to me to be speaking of something entirely different.