From one of St. Thomas's commentaries on Aristotle:
Surprisingly for anyone who believes medieval people all marched in theological lockstep, in ideological thrall to the Pope, one of the most cherished methods of education during the Middle Ages was debate. This passion for debate included not only debates before audiences (but with considerably more intellectual rigor than our political "debates" now) but debates carried on by correspondence. Debate was, in a way, part of one's own education, as students often had to argue opposing sides of issues using set texts like the Sentences of Peter Lombard. This was the purpose of his contemporary Abelard's Sic et Non, which set conflicting opinions of the Church Fathers against one another with the student's task being to argue both sides and/or resolve the seeming conflict. Not everyone received Abelard's book enthusiastically, especially since Abelard burned a lot of bridges during his career, but such a project—using preexisting authorities, compiling glosses, adding commentary, and, throughout it all, debating—was typical of medieval education.
Thomas Aquinas (1225-74) was himself no mean debater. As a student and teacher at the Universities of Paris and Cologne, he both hosted and participated in debates and wrote extensively in preparation for them. His Disputed Questions on Truth is one such work, in which Thomas introduces a controversial topic like predestination, knowledge, justification, or the relation between human choice and God's will, considers them from multiple angles, proposes his own answers, anticipates responses and answers those, and, via dialectic, works his way toward the truth of the topic in question.
This format, the posing of thesis and antithesis in a disputatio, was itself a form of debate and mirrored the disputationes of the medieval university. Thomas wrote most of his heavy theological and philosophical work this way, including his magnum opus, the unfinished Summa Theologica, and his Summa contra Gentiles, apparently an apologetic work meant to help Christians both defend their faith and present it to Muslims in understandable terms. Thomas's use of the disputatio makes for incredibly tedious reading, but that reading will also be profoundly instructive if one sticks with it. It takes a serious amount of intellectual honesty and—to use a buzzword—empathy to work this way, presenting the strongest arguments of one's opponents rather than setting up armies of straw men to knock down. One has to respect one's opponents to work this way. It requires the virtue of charity.
Thomas took debate seriously, especially when theological truth was on the line. One of the weightiest issues of his day was the Cathar heresy, a revival of the dualistic Manichean spiritualism of late antiquity. Briefly, the Cathars held that one's spirit is pure, the material world—including one's own body—was evil, and only by purifying oneself of attachment to the world and its attendant appetites could one be saved. (This heresy has by no means been expunged from modern Christianity, by the way. How many people do you know who look forward to release from "this body" and "eternity in heaven" instead of the resurrection?) The founder of Thomas's order, St. Dominic, traveled through the area of southern France where Catharism had most firmly taken root and repeatedly debated Cathar leaders.
The controversy continued into Thomas's day. According to a famous anecdote, when Thomas was invited to a banquet with Louis IX, the Crusader king of France, he sat mostly silent through dinner, apparently lost in thought. Suddenly, long after the partygoers had gotten used to his silence, Thomas pounded on the table and shouted, "And that will settle the Manichees!" Supposedly, Louis had a secretary fetched so Thomas could get his idea down while it was still fresh.
The story may or may not be apocryphal, but it illustrates something true about Thomas: the debate was never far from his mind, and the more serious the disputed question the more that was the case. But again—this care for the debate was always infused with charity. Charity was not, to Thomas, mere affection or the bundle of feelings and lusts that passes for love today, but specifically the habit of "friendship of man for God" which unites man to God, who is charity. This divine friendship, as God works through us, reflects like sunlight off of us onto those around us:
Loving your neighbor is loving God. So debate, but debate charitably, because bringing your neighbor to the truth is the loving thing to do. After all, that's what God is doing to us.
Abelard offers an instructive counterexample. Famous for his arrogance, Abelard was seldom content to defeat someone in debate on points—he wanted an intellectual knockout. He tried to humiliate his opponents and pointedly criticized major theologians and philosophers, including his old teachers, saying of one that he was famous out "of long established custom" and not because of "the potency of his own talent or intellect." After impregnating a student, whose relatives caught and castrated him, Abelard fled to the Abbey of St. Denis outside Paris—until he insulted the abbot and fled again. For the rest of his life, he resurrected old controversies and picked new fights. Like Galileo, who also provoked most of the hostility he encountered himself by being rude and pigheaded, Abelard found himself accused of heresy and facing excommunication by the time he died. A number of Abelard's ideas, particularly his dabbling in rationalist deconstructions of the Trinity, would still have put him beyond the pale doctrinally speaking, but his reception may have been warmer—more forgiving, more charitable—had he practiced a little charity himself.
I reflected a few weeks ago on the difference between quarreling and arguing. I think charity is the difference; it's the oil that reduces friction and overheating. We might be tempted simply to disengage, to shut off the engine, but that's a mistake. The truth is real and worth pursuing, and it's worth persuading others to join you in the pursuit—what's the point of debate if not to persuade? Charity makes debate, rather than screaming, tribalism, and virtue signalling, possible. Assume the best of your opponents, assume their good faith, and always give them yours.
If we can learn anything from Thomas right now, we can start there.