On Sept. 14, 1998, Pope St. John Paul II — whose feast the Church celebrates  on Oct. 22 — issued the encyclical Fides et Ratio on the relationship between faith and reason. John Paul II opened the letter with one of its most quoted lines: “Faith and reason are like two wings on which the human spirit rises to the contemplation of truth.”  

This both/and vision of faith and reason was not only something that John Paul II proclaimed; it was something he lived. A man of deep Catholic faith and Marian devotion, he was also a brilliant student of philosophy, drawing the phenomenology of Max Scheler into dialogue with the metaphysics of Thomas Aquinas and contributing to the movement of Christian personalism with texts like Love and Responsibility and The Acting Person.  

Now, almost 30 years later, Pope Leo XIV — a man trained in both mathematics and canon law — has echoed John Paul the Great in a recent message to the International Congress of Philosophy in Asunción, Paraguay.  

Like his predecessor, Leo warns about the dangers of a faith that demeans reason. Some believers, he notes, “have seen rational reflection — given that it arose in a pagan environment — as a threat that could ‘contaminate’ the purity of the Christian faith.” Leo likely has in mind here the famous lament of Tertullian — “What indeed has Athens to do with Jerusalem? What concord is there between the Academy and the Church?” — but he singles out, in particular, the “distrust of philosophy” in the Reformed theologian Karl Barth.  

Against this fideistic strain of Christian faith, Leo leans into his holy father Augustine: “Whosoever thinks that all philosophy is to be avoided wishes nothing else than that we do not love wisdom.” Reason, as Leo resolutely puts it, “is a gift expressly willed by the Creator.”  

At the same time, Leo warns against the opposite error: a rationality bereft of faith. Some thinkers, like the 19th-century German philosopher G.W.F. Hegel, end up “subordinating faith to the rational unfolding of the spirit” — an immanentized Christianity. Others jettison faith altogether, doing great damage to reason in the process: “We must not forget that philosophy … can also descend into dark abysses of pessimism, misanthropy and relativism, where reason, closed to the light of faith, becomes a shadow of itself.” Faith, Leo stresses, is a “gift” too; indeed, a far more important gift, for it’s born of divine grace and bears “the Good News, the message of salvation.”  

The answer, thus, is neither faith at the expense of reason, nor reason at the expense of faith, but both faith and reason in a harmonious exchange: “The deepest search of our intelligence tends towards wisdom, which is manifested in creation and reaches its culmination in the encounter with our Lord Jesus Christ, who reveals the Father to us.” Leo invokes St. Justin Martyr, St. Bonaventure and St. Thomas Aquinas, all of whom demonstrate “that faith and reason are not only not opposed, but support and complement each other in an admirable way.” (One could, of course, add countless other names to the list, including many great scientists who were also Catholic priests, such as Gregor Mendel and Georges Lemaître.) He then quotes John Paul II directly from Fides et Ratio: “The intimate bond between theological and philosophical wisdom is one of the Christian tradition’s most distinctive treasures in the exploration of revealed truth.” 

As a “son of St. Augustine”— indeed, Leo references the “Doctor of Grace” three times in this brief letter alone — it was inevitable that this theme of the harmony of faith and reason would come to the fore during Leo’s pontificate. Augustine is, with Aquinas, arguably one of the two greatest minds that the Church has ever seen; to read through his City of God, or simply to behold both the sophistication and prolificacy of his output — the equivalence, according to once scholar, of “writing a 300-page printed book every year for almost 40 years” — is to experience the harmony of faith and reason at full volume. One could also read this letter as teeing up Leo’s forthcoming reflections on AI (a key priority of his pontificate), which will require both a firm grounding in the resources of the Catholic tradition and an openness to the benefits of this new technology. 

Leo’s message of the harmony of faith and reason is especially important coming from the first Pope from the United States, where these two sources of Western culture (Jerusalem and Athens, Hebraism and Hellenism) have historically had a cold if cordial relationship. America is, at bottom, a deeply Christian country, as well as a sharply scientific and technological one. But Americans typically treat these two enterprises of faith and reason as belonging to entirely different worlds, with little intrinsic connection between them.  

To these mirrored one-sided paths — a faith that tends toward the irrational and a reason that tends toward the utilitarian (“when so many things, and even people themselves, are seen as disposable”) — Leo underscores the mediating power of philosophy, which “has much to question and much to offer in the dialogue between faith and reason and between the Church and the world.” 

Leo’s letter constitutes an important reminder of this key both/and in the history of the Catholic Church — and a wonderful remembrance of the great Pope who incarnated it so brilliantly.