Thomas Acquinas: A Doctor for the Ages

By Romanus Cessario, O.P., is Professor of Systematic Theology at St. John’s Seminary in Brighton, Massachusetts.

Why should a medieval Catholic priest merit a place among the most important figures of the second millennium? In part because more than seven centuries after his death his writings and teachings still seem fresh and—more importantly—true. His genius as a thinker and teacher has led thousands of scholars to carry on the intellectual projects and hand on the teachings in philosophy and theology of this thirteenth-century Neapolitan Dominican friar, whose physical size and taciturn spirit prompted some of his youthful confreres to label him the “Dumb Ox.” But you don’t have to be a Thomist to appreciate the genius of Thomas Aquinas (1224/5-1274). This Doctor communis has something to offer everyone who is serious about searching for the truth. He is a Doctor for the ages.


Thomas Aquinas was born to a landed aristocratic family that played a conspicuous role in the turbulent political life of the early thirteenth-century Italian peninsula. But unlike Augustine of Hippo, also a foundational doctor of the Western Church, Thomas d’Aquino, notwithstanding his prolific writing, surrenders very few details of his own biography, and so our knowledge of his family interactions and other personal matters remains limited, almost all coming second-hand, mostly from hagiographers. At the same time, the saint’s theological and philosophical compositions disclose both his own spirit as a Christian believer and the magnitude of his intellectual acumen.

Aquinas was born and spent his early years in the Kingdom of Sicily. It was a time when Frederick II (1194-1250) and Pope Gregory IX (c.1148-1241) were at warring odds with one another. In 1239, when Aquinas was fourteen, the Pope excommunicated Frederick, who had initiated an invasion into the Papal States as part of a long-delayed offensive against the Lombard communes. This momentous clash between civil and ecclesiastical authority was only the first of many conflicts that would dominate the social circumstances in which Aquinas constructed his massive corpus of theological and philosophical writings. Later at Paris, new conflicts, on the one hand between Churchmen and religious orders and on the other between Aristotelian philosophers and Augustinian theologians, again provided both background and stimulus for Aquinas’ intellectual work. And later still in Italy, long-standing antagonisms between the See of Rome and the churches of the East—aggravated by a then two-hundred year old schism—significantly influenced the way that Aquinas would deploy his intellectual energies. Even towards the end of his life, Aquinas was compelled to confront conflictual circumstances, but this time they took the form of intramural squabbles among his fellow Dominicans, some of whom still thought that ordained ministry could best be learned after the fashion of a guild-craft, while others, inspired by Aquinas’ own example, understood that the Christian priest, because he participates in Christ’s own mediation, requires a scientific instruction in the deposit of saving truth.

The political conflicts that affected Aquinas’ personal background resulted, for the most part, from the growth and strengthening of centralizing tendencies in both ecclesiastical and secular affairs that took place at the beginning of the thirteenth century. The unprecedented expression of political as well as of theological unity in the Church achieved by Pope Innocent III at the Fourth Lateran Council in 1215 inaugurated this period of profound cultural change. Alasdair MacIntyre argues that these conditions exercised an influence even on Aquinas’ treatment of such speculative concepts as natural law. Certainly, one cannot appreciate fully the kind of stability that Aquinas’ theology and philosophical investigations introduced into the world of Christian thought without bearing in mind the turbulence that marked the social, political, and ecclesiastical milieus during his lifetime.

The social changes occasioned by the transition from feudal to urban Europe formed the background for the scholastic revival of the thirteenth century. Contrary to some accounts, European culture before the sixteenth-century renaissance was not darkly glum. In fact, Christian civilization in the West underwent an extraordinary renaissance in the twelfth century, when a massive effort was mounted to retrieve and organize past learning in diverse fields. This development enabled Aquinas to make creative use of the many philosophical advances that accompanied the introduction of Aristotle to the West.

During his education with the Benedictine monks at Monte Cassino and later in Naples at the first European university to operate under entirely secular control (which Frederick II founded in 1224), the young Thomas Aquinas enjoyed the usual prerogatives of his social class and standing. It seems that his parents had plans for their son to pursue an ecclesiastical career of distinction. The direction of his life changed dramatically, therefore, when he abandoned his family’s aspirations and joined the newly established brotherhood of Dominicans. The traditional accounts of his attempt to join the friars, which include tales of imprisonment and attempted seduction, reflect the emotional conflict that Aquinas’ decision created within his family.

Studies in Paris and Cologne followed. In these high centers of intellectual life, Aquinas joined other young Dominicans who had been placed under the tutelage of Albertus Magnus, the early Dominican theologian and natural philosopher. His education was not only traditional, involving close studies of the Scriptures, of the Western Fathers, and of Church law, but also innovative, inasmuch as Aquinas discovered the new wave of Aristotelian philosophy, which included the areas of natural, moral, and “rational” (rhetoric, grammar, and logic) philosophy.

Between 1252 and 1259, Aquinas fulfilled with signal success the obligations of a thirteenth-century university instructor and professor, notwithstanding the conflicts and disputes that continued both within and outside the lecture halls. On one occasion, the French king had to station the royal archers around the Dominican convent in Paris to defend the friars against attacks from partisans of the secular masters. These secular clerics (secular meaning not a member of a religious order) found it difficult to accept the new friars into their ranks. In the midst of this turmoil, Aquinas had to meet rapid changes in theology and became adept at navigating the intellectually challenging waters of the medieval scholastic disputatio. On August 15, 1257, both he and the Franciscan doctor Bonaventure were admitted to the consortium magistrorum, that is, they were recognized as full members of the professorial corps.

In 1259 Aquinas returned to the Italian peninsula, where he accomplished a variety of tasks in service to both the papacy and the Dominican Order. These tasks included preaching sermons not only to the papal household, but also to the inhabitants of the cities where the Pope was residing. Today at Orvieto one can still see an outdoor pulpit that Aquinas mounted to preach the Word of God and still read sermons Aquinas preached in his native Neapolitan dialect. In the midst of duties as theological advisor for the papal curia, he also found time to teach theology to young Dominicans. The Summa Theologiae dates from this period. This systematic tract was intended to cultivate the preacher’s ability first to ponder and then to communicate the gospel, and so served as a tool to fulfill the Dominican ideal: To contemplate and to give to others the fruits of one’s contemplation.

Circumstances of conflict, however, once more directed the development of Aquinas’ apostolic activity, bringing him back to Paris for a second period of teaching between 1268 and 1272. There he devoted his energies to allaying the uneasiness that the pagan philosophy of Aristotle caused among theologians of a more traditional Augustinian persuasion, while at the same time he critically engaged those who used philosophy to contradict the truths of Christianity. Thinking about the faith is always risky business. Some people are frightened by the prospect, and so fall back into a kind of credulous fideism that explains Christian doctrine by appeal only to the categories one finds in revelation itself. Others become intoxicated with the project, and so construct a kind of censorious rationalism that trims the supernatural content of divine revelation in order to fit the categories established by human reason. Aquinas’ merit is that he succumbs to neither temptation.

During his second Parisian stay, Aquinas continued his battle in defense of the mendicant religious orders, in particular the Franciscans and Dominicans, whose newly authorized place within the university structure continued to cause tensions among the already-established secular masters. Before the advent of the mendicant orders, religious priests were for the large part found only in monasteries, and so avoided day-to-day involvement in Church affairs. Francis and Dominic brought the monastery to the cities and towns of Europe, and so intruded into an arena that up to that time had been dominated by a diocesan bishop and his clergy. Feelings ran high. We know of only two times in his life when Aquinas lost his composure, and one occurred when he learned that certain persons were cornering prospective students in the back streets of Paris in order to dissuade them from attending the lectures of the mendicant masters.

After the three-year cycle of lectures and disputations that constituted in the thirteenth century a term of office for the friar who held the Dominican chair at the University of Paris, Aquinas returned once again to Italy. At Naples, he took up his academic work, teaching Dominicans about the Bible and continuing to write his Summa Theologiae . But providence was about to intervene in a dramatic way.

During his first sojourn in the Papal States, Aquinas had composed a compendium of arguments to be used by the theologians charged by the Pope with carrying on dialogue with schismatic Byzantine theologians. So when Gregory X convoked a council at Lyons for May 1, 1274 in order to achieve mutual understanding with the separated Greeks, he numbered Aquinas among the experts who were asked to join the deliberations. While traveling northward from Naples, Aquinas suddenly fell ill, and on March 7 he died in the early hours of the morning at the Cistercian monastery of Fossanova.

Faithful to his profession of mendicant simplicity and to the Dominican objective of preaching sacred truth, Aquinas, during the course of his adult career, politely but firmly refused both the abbacy of Monte Cassino and the archbishopric of Naples. The first he declined at the start of his ministry, the second at its end. By these decisions, he disengaged himself from parochial conflicts, and so was free to make a permanent contribution to theological learning in the universal Church.

What is that permanent contribution? In his 1988 Gifford Lectures, Alasdair MacIntyre explained that Aquinas’ approach to theology provides a standpoint that is coherent, comprehensive, and resourceful in its ability to deal critically and creatively with opposing views. This is not to say that Aquinas supplies the software that fits all hardware. Diversity marks his legacy. From the years following his death until the late fifteenth century, the label of “Thomist” was generally applied to those who emphasized the created world, instead of the divine ideas, as the foundation for acquiring knowledge. The ecclesiastical condemnations of Aquinas’ teaching in 1277 and 1284, even though moot long before their formal revocation shortly after Aquinas’ canonization in 1323, reveal the kinds of difficulties that attended a transition to the new theological forms that Aquinas’ teaching embodied. The censures, to be sure, were politically motivated, but they reveal a traditional preference for the heritage of Bernard of Clairvaux over that of Anselm of Canterbury. In brief, commentary was safe, whereas thinking was risky. Some refer to this period as “first Thomism,” when the opposition to Thomist propositions arose mainly from tradition-bound theologians who were persuaded that in the end it was a mistake for a theologian to take nature too seriously.

The diverse ways that theologians explained both the origin of human knowledge and the ground for the certitude of that knowledge illustrates the kind of issues that marked this transition. At the beginning of the thirteenth century, the received tradition explained human knowledge by appeal to some variety of divine illumination. In short, God infused into the human mind whatever was required to acquire true knowledge. Illuminationists generally conceived of the soul as a mirror or receptacle ready to capture the rays of intelligibility from the Divine Mind. While such a view enjoyed the advantage of placing human intelligence into a fixed and comfortable relation with the Supreme intelligence, it also asserted that only divine illumination guaranteed that the human being obtained true and trustworthy knowledge of sensible realities.

As a result of reading Aristotle, Aquinas had come to a different conclusion about achieving certitude in knowing. Rather than looking to illumination in order to guarantee the authenticity of the created world, he argued that the created world itself, the world of mobile nature and natural things, possessed its own intelligibility and, furthermore, that God had equipped the human mind to capture it. What is more important, he argued that since human beings know the reality of the world, they also can move demonstratively from this sure knowledge back to a sure knowledge of God, at least as He is the cause of this creation. Aquinas pointed out at least five different ways in which this argument could proceed. In sum, Aquinas took away the skyhooks, and the theological world did not collapse. The problem is a perennial one, and there are still theologians who look for ways to put the skyhooks back up. In any event, it took time for some of his contemporaries to accept Aquinas’ innovations in theological argument, and this explains the controversies that erupted after his death.

By the time of the sixteenth-century Protestant reform, work on Aquinas had become more identified with straightforwardly theological issues, as exemplified in the influence that his Summa Theologiae exercised on the Council of Trent. Those who criticized the “Common Doctor” did so because they considered either his theology not sufficiently humanist or his humanism not fully radicalized. This “second Thomism” continued to flourish widely during the early modern period. Witness that during the second half of the seventeenth century, for example, two Chinese translations of the Summa were published in Peking.

In the decades after the European revolutions of the late eighteenth and early nineteenth centuries, the Church again turned to Aquinas’ works to solve problems mainly of a philosophical nature. This “third Thomism” is more commonly known as “neo-Thomism.” Some post-Vatican II theologians, it is true, supposed that neo-Thomism signaled Thomism’s last breath, but John Paul II has recently offered another assessment. Speaking of Aquinas, the pope says, “In him, the Church’s Magisterium has seen and recognized the passion for truth; and, precisely because it stays consistently within the horizon of universal, objective, and transcendent truth, his thought scales ‘heights unthinkable to human intelligence’” (Fides et Ratio, no. 44).

The teaching of Thomas Aquinas has exercised an active influence mainly but by no means exclusively on Western intellectual movements for three-quarters of the millennium that is now coming to a close. The legacy of Aquinas to world culture flows like a winding river through many different terrains, while its waters pick up sediments from the different geological formations that form its bed. During its more than seven-hundred-year history, Thomism has influenced nearly every field of human learning, and Thomists have found themselves geographically dispersed, albeit unevenly, throughout the whole world.

Interest in Aquinas spread quickly after his death. Since the new mendicant orders sent their students to learn theology in places such as Paris and Oxford, Aquinas’ works were first studied principally in the university cities of Europe. The earliest Thomists gathered around these new centers of learning as well as those at Cologne, Bologna, and of course Naples. The study of Aquinas then followed the development of the universities in Italy, Spain, Portugal, Germany, Bohemia, Vienna, Cracow, and Louvain. In the period before the Council of Trent and during its sessions, the major Thomists worked in Southern France and in Northern Italy, whereas in the post-Tridentine period, Aquinas’ legacy flourished principally in Spain and the Spanish Netherlands. It was not until 1611, when Spanish Dominicans established a university in Manila, that Aquinas’ works spread to the New World, and from there even to the Far East. In the twentieth century, Aquinas flourished in both Europe and the United States, and even rekindled Asian Thomism in authors such as the Japanese Yoshinori Inagaki.

Aquinas’ legacy is not only found everywhere, but also has had an impact on every branch of higher learning. In the decades immediately following Aquinas’ death, Thomists continued to welcome the introduction of Aristotle into the West, and so challenged many theological truisms. Later, in the sixteenth century, Thomists answered the objections raised by the Protestant reformers against the Church’s teaching on justification, the sacraments, and the nature of the Church herself, while others were developing the theoretical groundwork for contemporary international law. From the start, then, Aquinas inspired discussions that range from mystical theology to cosmology, and from political theory to personal morality. Those who followed him, whatever their differences, shared the basic conviction that to think and teach and write ad mentem S. Thomae Aquinatis remains a sure guide to the truth of the Christian faith and of the human person. That influence extends to our time: It would be impossible to understand the debates and documents of the Second Vatican Council without acquaintance with the principal theses that discussions influenced by Aquinas had developed over the course of nearly seven centuries.

We learn something important about both theology and philosophy from this wide-ranging legacy. On the one hand, we learn what makes theology to be just that, a “word about God.” On the other, we learn that philosophy draws the human spirit up toward “heights unthinkable to human reason.”

Aquinas proceeded on the supposition that all theological writing ought to express the unity of divine truth; in his phrase, theology is like an impression of the divine knowledge in the created mind. Because he grasped this connection, Aquinas would reject today’s tendency to regard theology as a constellation of diverse fields of specialized inquiry whose only unity derives from the fact that they somehow coalesce to promote Christian service. Instead he held theology to be a single divine science about God, which is able to express the one divine knowledge that governs without qualification everything that exists. In other words, Aquinas was persuaded that the best theology reflects the simplicity of God whose knowledge of himself remains the one source of all true wisdom.

Aquinas’ own compositions do not fit easily the modern categories that theologians use to classify and describe their work. He was, in those terms, neither a researcher nor a theorist. On the contrary, Aquinas appreciated the unity of truth that flows from the divine simplicity, and would have been deeply repelled by conflicting truth claims produced by theologians asserting expertise in one or another theological discipline. At the same time, because Aquinas understood that theology is about ordering truths to the one Truth, and not assembling facts about many different topics, none of his works fits the literary genre of the encyclopedia, which always depends on recent research to modify what until that moment had been provisionally considered as true. Put differently, Aquinas recognized the formal difference that distinguishes theology as a divine science from religious studies as a human one. The latter always remains bound by the limits that reliance on a purely rational form of inquiry imposes. By sharp contrast, the theologian is possessed of something more.

A particular conception of the unity of theology did not keep Aquinas from developing a proficiency in diverse forms of theological and philosophical composition. Not counting his earlier expositions of certain Old Testament books—Isaiah, Jeremiah, and Lamentations—which he composed while studying with Albertus Magnus in Cologne, Aquinas produced during his relatively brief professional career (1252-1273) a body of literature that includes works of every description: theological syntheses, disputed questions, biblical commentaries, commentaries on Aristotle, commentaries on other classical works commonly in use at medieval universities, polemical writings, treatises on specific subjects, letters and replies to requests for expert opinions on particular issues, liturgical works, sermons, and prayers. All in all, a rich array of publications for one thirteenth-century man to produce within a period of little over twenty years, even taking into account the fact that he was at times aided by as many as four secretaries. Of course, Aquinas himself would not have agreed. Toward the end of his life he compared everything that he had written to straw, and like St. Paul he preferred above all things to know the Lord Jesus, who, according to the received account, himself spoke to Thomas from a crucifix hanging in the St. Nicholas chapel: “You have written well of me, Thomas! What do you desire?” To which, Thomas replied, “ Non nisi te, Domine.” Only you, Lord Jesus. Because his own “words about God” drew Aquinas back to God, the Church sees in this Dominican the model of a true theologian.

At the same time, we can learn from Aquinas’ legacy about the importance of philosophy for undertaking theological investigation. In the early part of the present century, when the revival of interest in Aquinas inaugurated by Pope Leo XIII was reaching its full vigor, certain ecclesiastical authorities decided that it would be useful to express Aquinas’ philosophical principles in the form of short theses or propositions. Although this objective, undertaken in the aftermath of the Modernist crisis, aimed more toward promoting a sound pedagogy than creating a narrow ideology, the Church did give quasi-official recognition to The Twenty-Four Theses that were held to embody the essentials of realist philosophy to be found in Aquinas’ writings.

We can indicate only some of the principal positions this effort promoted. The Thomist philosopher is best described as a metaphysical realist, who judges the conclusions, at least in their classical expression, of both idealism and positivism as untenable. The latter denies the existence of universal ideas, at least in the mind of creatures, whereas the former rejects the epistemological principle that nothing exists in the intellect that was not first in sense knowledge. In natural philosophy, Thomists defend the realism of creation, or what some theologians might want to designate the scandal of creation. In natural theology, Thomists hold the conviction that from the visible things of the universe the human mind can know the existence of God, who enjoys his own subsistent fullness of pure actual being, and who possesses no limitation of any kind, because nothing of potential remains in Him. No creature enjoys this status of pure act, and so Thomists espouse in metaphysics what Father James Weisheipl calls the “disturbing distinction” between essence and existence, which entails by way of corollary the conviction that every creature depends on the actuality of borrowed existence. Thomists think only in terms of analogical predication, such that the metaphysical concept of being is analogically, not univocally, said of God, substances, and accidents. In moral philosophy, they also argue for the primacy of intelligence in determining what is true about the moral life. While some Thomists espouse other theses in philosophy, this brief catalogue of philosophical views illustrates those held by any thinker who claims to stand in historical continuity with the teachings of Thomas Aquinas.

We can understand the Holy See’s decision to promote the philosophical standpoint of Aquinas by reference to the traditional way of depicting the 1879 encyclical of Pope Leo XIII, Aeterni Patris : “On the Restoration in Catholic Schools of Christian Philosophy According to the Mind of the Angelic Doctor Saint Thomas Aquinas.” The encyclical itself does not carry this title, but Pope Leo described it in that way the following year when he declared Saint Thomas to be the patron of studies in Catholic schools.

The reference to “Christian Philosophy” recalls that neo-Thomism, as it would later become known, was promoted by the Church in response to the widespread use of Cartesian manuals of philosophy in Christian education. Seminary training was especially affected, and this realization generated well-grounded fears that a new generation of priests would find themselves not only unfamiliar with the integrity of Catholic faith but also tempted to separate truth from experience. Rationalism does not prepare the mind to believe that God sent his Son into the world to be its way, truth, and life. Recall that Aquinas, as Pope John Paul II has confirmed, produced a philosophy of “what is,” not of “what seems to be.” Reality offers much more to philosophize about than do appearances. Pope Leo wanted to steer Church thinking away from the fascination with the apparent that had captivated European thought in the modern period, and we can see in retrospect that his initiative promoted a flowering of Catholic intellectual life.

Aquinas inspired much of the theology and philosophy that flourished in Catholic circles during the period between the two World Wars, and his teaching continued to receive papal endorsements after the Second Vatican Council. Pope Paul VI used the ceremonies that marked the seventh centenary of the death of Saint Thomas in 1974 to commend an “authentic fidelity to Thomas.” The 1983 revision of the Code of Canon Law further applauds Aquinas as a master who can lead students of theology to a deep penetration of the mysteries of salvation (CIC 252 § 3). A few years earlier, the same theme had appeared in the 1979 Apostolic Constitution Sapientia Christiana (especially Nos. 71 & 80), which presently governs the administration of ecclesiastical universities and faculties. Finally, the 1998 encyclical letter of John Paul II restates the confidence that the Church places in Aquinas as a thinker capable of leading people to a knowledge of the truth. Although Fides et Ratio enforces no allegiance to a specific set of philosophical theses, it does condemn those intellectual positions that faithful adherence to Aquinas inhibits: eclecticism, historicism, scientism, pragmatism, and nihilism.

In Fides et Ratio the Pope also acknowledged the enduring originality of Aquinas’ approach both to thinking about the truth that God has revealed in Christ and to expressing the harmonies that arise once the rational creature is enabled to ponder what “eye hath not seen” (Isaiah 64:4). What is perhaps more pertinent for earning recognition in the second millennium, the Pope also cited Saint Thomas “because of the dialogue which he initiated with the Arab and Jewish thought of his time” (no. 43). Whatever its source, Aquinas, we are told, revered the truth. No wonder popes have reserved for him the distinguished epithet, “apostle of the truth.”

It is Aquinas’ profound love for the Incarnation that makes him still a faithful guide for preserving the Christian Church from errors that erode her confession of the gospel of Jesus Christ. Aquinas knew that because God chose to save the human race by sending his only Son in the likeness of sinful flesh, the Church of Christ is committed to reconciling the human and divine. Aquinas teaches us the right way to view the creation of the world with the new creation of the gospel. There is every reason, therefore, to suppose that at the end of the millennium about to commence he will still rank among the figures who have most influenced the course of human intellectual activity. The desire to know the truth that God has placed in the human heart will not disappear, nor will the two wings of faith and reason on which the human spirit rises to the contemplation of this truth. Thomas Aquinas illumines the dynamics of this upward flight.