The past century and a half of papal teaching on modern times often seems a tangle: any number of different strands”theology, Thomistic ­philosophy, social theory, economics”all snarled together. And yet a little historical analysis may help loosen the knot. In fact, a careful reading of papal documents reveals one of the main causes of the tangle. Throughout Catholic thought over the past hundred and fifty years, there have run two entirely distinct conceptions of modernity and two quite different uses of Thomism”a combination of four threads weaving in and out of the Catholic Church’s response to the strangeness of modern times.

For example, several modern popes have championed the thought of St. Thomas Aquinas, but they did so in very dissimilar ways. At times, a reactionary, ­legislative, and disciplinary form of Thomism was deployed, directed inward at members of the Church, chiefly about uses of philosophy in the study of sacred doctrine. At other times, Thomism was allowed to play a more constructive, synthetic, and open role, directed outward to the world, chiefly on questions of social and political order.

Meanwhile, modernity came to be seen in two ways. There were the economic, political, and legal problems of modernity”the aspects of modern life that made necessary the development of “social doctrine.” And yet modernity was also understood as a philosophical and theological system that displaced, or at least threatened, what could be called the praeambula fidei ”the “preambles of faith,” which include the truths of natural reason, particularly on philosophical issues close to sacred doctrine.

An examination of the historical documents can trace each of these distinct threads”and, along the way, solve some of the puzzles of Catholic intellectual history. The two Thomisms and the two Modernisms do not line up, but their interplay helps explain how St. Thomas’ moral, legal, and political thought was gradually detached from his metaphysical and theological thought. And it helps explain, as well, why John Paul II used so much of his papacy in an effort to reunite the Church’s understanding of both Thomas Aquinas and modernity.

Until the late nineteenth century, the word­ modern was rarely used for describing or listing errors. Indeed, in the eighteenth century Catholicism had comfortably”perhaps all too comfortably”adapted itself to many aspects of modernity. So, for instance, with the discovery of the New World and the rush of Catholic missions to far-flung lands, many Catholics understood that they were living in a new era of exploration, industry, education, art, literature, devotion, science, and philosophy.

The Reformation and the religious wars, culminating in the 1648 treaties of Westphalia, destroyed the old medieval common law of Christendom by creating a system of states having diverse confessional allegiances. A new common law, however, evolved among the ­peoples under Catholic rule. It was built on a complex and evolving set of treaties, informal agreements, and legal fictions through which the Church conceded to Catholic sovereigns rights over many aspects of ecclesiastical life”in exchange for which those sovereigns protected the Church from schism and supplied the resources for missions across the world. The sovereigns were deemed junior apostles, entitled to rule “in trust” the everyday life of the Church in Europe and her colonies.

Catholicism thus developed a remarkable symbiosis with the new system of modern sovereignty”so long as it was in the hands of Catholic families. This political system is what writers in the nineteenth century called the ancien régime , because Catholics had no living memory of any other order. But it was, in fact, neither ancient nor medieval. It was, instead, something quite modern”and for the Church it worked, off and on, reasonably well.

The French Revolution, however, upended this modern system of religious and political Christendom. France’s 1790 Civil Constitution of the Clergy gave church governance not to the mischievous yet familiar Catholic families but to the nation, and this French model soon spread elsewhere, particularly to the ­former European colonies in Latin America. The ­clergy became civil servants, elected by democratic vote. In other words, modernity saw the transference of rights that had once belonged to the Church itself. Catholic kings received those rights first, but the nation-states would soon inherit them”nation-states that were, as often as not, governed by a doctrine of often anti-Catholic laicism.

After the defeat of Napoleon in 1815, the Congress of Vienna attempted to restore the earlier model of a religious sovereign”the union of throne and altar, brought back to tamp down the fire of social rebellion. Thus, encyclicals of the era urged Catholics to obey legitimate authority, beginning with the pope’s own temporal authority in the Papal States. But the revolutions of 1848 swept aside the Restoration, and, with the 1864 Syllabus of Errors, something we might call the Paper Wars commenced.

The Syllabus of Errors derives from one simple historical fact: In 1860, Pius IX lost his Italian dominions to the House of Savoy, and the Papal States came to an end. The immediate effect was the removal of the pope from the political problems of governing, but there was a second and unexpected effect: Along the way, the papacy lost the inhibitions about speaking on political matters that actual rulers must have. But how should the Church speak? There had been no systematic political theology for two ­centuries, so Pius IX and his advisers cobbled together a number of pontifical statements and admonitions, grouped them under various headings, and fired away.

The Syllabus of Errors was the result. Attached to the encyclical Quanta Cura , the Syllabus lists eighty condemned propositions, and even the most sympathetic churchmen quickly realized the problem of ­carrying on a theological discussion in this way. ­Published in a new era of daily newspapers and the telegraph, the list of errors instantly reached millions of readers, nearly all of whom were confused.

The format was particularly vexatious: Almost every erroneous proposition is stated in the affirmative, leaving the reader to puzzle out the correct Catholic view by negation. So, for example, the eightieth proposition condemns the idea that the pope is obliged to “reconcile himself to contemporary liberalism.” The negation might be that “the pope is obliged not to ­reconcile himself to contemporary liberalism,” or it might be that “the pope is not obliged to reconcile himself to liberalism (though he could, if he wanted).” It might even be that “the pope is obliged not to reconcile himself to contemporary liberalism (but liberalism understood in some other way might be all right).”

Still, despite such confusions, Pius IX had a clear target in mind with the Syllabus . This was not a ­disciplinary encyclical on matters inside the Church. Over and over, in seventy-three of the eighty propositions, the Syllabus takes aim at the modern common law of Christendom. Pius IX flatly rejects the rights once exercised by Catholic sovereigns and then by nation-states. He declares, in effect, the independence of the Church not only in matters of ordinary governance (sacraments and the episcopacy) but also with regard to schools, religious orders, marriages, families, and sodalities.

Late in 1869, the First Vatican Council convened. Parts of the Syllabus were reworked into five chapters and twenty-one canons of the first draft of a conciliar document, De Ecclesia Christi , where they seemed to add up to something like a separation of the Catholic Church from the formerly Catholic states. In the end, the chapters and canons drawn from the Syllabus were dropped when the bishops could not agree about any overarching theory to unify them. They did agree that the Church is independent of the nation-states. And, on that principle, they reconfirmed the universality of the Church, giving the papacy universal jurisdiction to try to solve the problem, and went home.

The result was that, when Leo XIII was elected pope eight years later, he inherited an incomplete ­revolution. He had no new catechism or full set of ­conciliar doctrines, and no part of the revolution had been canonically codified. He inherited a fact rather than a coherent theory.

At least two things needed to be put into some kind of synthesis: the Syllabus of Errors and Vatican I’s ­constitution for the Church, Dei Filius . The Syllabus would need to be converted not merely into negations but into a positive civil doctrine. For that matter, Dei Filius asserted that God is the “Lord of the Sciences,” that faith and reason have distinct yet mutually ­supportive objects and ends, and that the “assent of faith is by no means a blind movement of the mind.” The preambles of the faith, in other words, needed to be clarified and organized for modern times.

For his answer, Leo chose to move the school he had founded, the Academy of St. Thomas Aquinas, from Perugia to Rome and to make cardinals out of two of its faculty members (including his brother). A year later, in 1879, he issued his great philosophical encyclical, Aeterni Patris .

Aeterni Patris insists that a sound philosophy is needed “in order that sacred theology may receive and assume the nature, form, and genius of a true science.” He advocated the wisdom of St. Thomas Aquinas as the modern antidote: “While, therefore, We hold that every word of wisdom, every useful thing by whomsoever discovered or planned, ought to be received with a willing and grateful mind, We exhort you, venerable brethren, in all earnestness to restore the golden wisdom of St. Thomas and to spread it far and wide for the defense and beauty of the Catholic faith, for the good of society, and for the advantage of all the sciences.”

What Leo saw is this: The issues of faith and reason highlighted in Dei Filius could not be advanced by philosophical eclecticism. Since the sixteenth century, he complained, philosophical systems have “multiplied beyond measure,” and even Catholic philosophers have accommodated themselves to a curricular mentality that “depends on the authority and choice of any professor.”

Leo proposed that Thomas be held out as the “Master” whose doctrines must enjoy “excellence over others””but his purpose was not to reduce the Catholic mind to a homogeneous Thomism. Rather, it was to achieve an integrated response to issues that were both theological and political. When we read Aeterni Patris as a whole, we see that Leo framed the revival of Christian philosophy chiefly in the context of the ongoing political problems: “False conclusions concerning divine and human things, which originated in the schools of philosophy, have now crept into all the orders of the State.” Indeed, throughout Leo’s work”in the some 110 encyclicals and other teaching letters”Thomas is rarely discussed or referenced apart from social and political problems.

Leo’s two aims”picking up the pieces from the Syllabus and fleshing out Dei Filius ”were not without tension. In the subjects close to sacred doctrine, it was crucial to achieve a rather tightly organized account of the relation between philosophy and the deposit of faith. Even slight changes in the philosophy entail new estimations of the doctrine. Social and political issues, however, allow much more room for creative maneuver, and there emerged a kind of broad Thomism ­suitable for these issues. Thomists developed rather freewheeling accounts of the political, economic, legal, and social order, and they showed considerable ­ingenuity in making their accounts look continuous with the work of the Angelic Doctor.

Turning away from the example of Pius IX, Leo undertook a new kind of paper war. He took the outmoded structure of a medieval scholastic article (for example, what we find in St. Thomas’ Summa Theologiae , with the question, the objections, the sed contra , the response, and the replies to objections), changed the questions, and rebuilt the article in the prose of an encyclical teaching. It was in part dialectic, in part systematic, and in part apologetic. There was no need to make lists of errors that would leave Catholics scratching their heads.

The affirmations to be negated in Pius IX’s 1864 Syllabus became affirmations to be affirmed in Leo XIII’s famous 1891 encyclical Rerum Novarum ”­positive statements of Catholic teaching on modern social and political issues. The underlying Thomistic doctrine gave the body of work at least the appearance of coherence, and, as Leo’s papal successors, together with lay and clerical scholars, continued the project, there emerged a remarkably structured but evolving body of social doctrine.

All of this makes more curious Pope Pius X’s sudden condemnation of Modernism, which appeared in two documents in 1907. On July 3 of that year, the Vatican published a decretum called Lamentabili Sane , containing a syllabus of sixty-five Modernist propositions to be condemned. Two months later, on September 8, the pope issued the encyclical Pascendi Dominici Gregis . Admitting that his exposition was unusually prolix and didactic, Pius X insisted that such was necessary to deal with Modernism as a “whole system,” indeed as “the synthesis of all heresies.” Modernists were accused of reducing ­revelation to experience, Scripture to history, and doctrine to evolving symbols.

If, however, we examine the condemnations with an eye to the pattern of two Modernisms and two Thomisms, much comes clear”for Pius X had gone back into the mode of making lists of errors, but he focused his attention not on social modernity but on the doctrinal and metaphysical aspects of modern thought. Lamentabili Sane not only listed sixty-five errors; to complicate matters, it also referenced the 1794 encyclical Auctorem Fidei , which condemned eighty-five further propositions in connection with Jansenism. A scrupulous scholar under ecclesiastical discipline now found himself reckoning with 150 propositions”230, if the Syllabus of Errors is added in. Who could keep track of all these errors?

In January 1908, Wilfrid Ward, editor of the Dublin Review , proffered obedience to what he called “the act” of the Holy See condemning the doctrine of the Modernists. He was not pleased, however, with what he called “the document.” He complained that it left too vague the origin, definition, and scope of Modernism. It was clear enough, Ward conceded, that the pope wished to condemn the principle of “subjectivism in religion.” But the encyclical’s generalizations and “isolated passages” could too easily furnish partisans with cudgels with which to censure certain books and theologians, to say nothing of any number of merely half-baked ideas that were not mentioned in the encyclical itself.

To a certain extent, Leo XIII had had the easier ­battle, turning outward to fight in the social world for the institutional survival of the Church and the array of social institutions clustered around it. The battle of Pius X was, instead, turned inward to the Church itself; as a result, the Vatican came to seem a constant bully, obsessed with tracking down heretical or confused professors in the seminaries.

Still, in many ways, Pius was forced by events to make this inward turn and take up the set of issues that stood close to sacred doctrine. In Lamentabili Sane , only six of the sixty-five propositions remotely touched on Leo’s social and political topics. For Pius, the “synthesis of all heresies” was a different sort of Modernism. At least in the sphere of sacred doctrine (and the metaphysical principles conjoined to it by way of faith’s preambles), the Church could make no ­compromise. Neither could there be a development analogous to what was already underway in social teaching. Leo had put Thomism in an offensive mode as far as social doctrine went. Pius X made clear that, in matters related to sacred doctrine, Thomism would be put into a defensive role.

For Pius, the sure sign of Modernism was derogation from, or even disparagement of, scholasticism. “Whether it is ignorance or fear, or both, that inspires this conduct in them, certain it is that the passion for novelty is always united in them with hatred of scholasticism, and there is no surer sign that a man is tending to Modernism than when he begins to show his dislike for the scholastic method.” To be heard carping at scholasticism was a ground for dismissing faculty and administrators at ecclesiastical schools.

Lest there be any doubt what is meant by scholasticism , Pius X issued in 1914 a motu proprio called ­ Doctoris Angelici , which put the Thomistic norm for studies (in degree-granting ecclesiastical schools) explicitly under precept from the Holy See. To curb the private opinions of professors, Pius X ordered that the Summa Theologiae itself be used as the text of the ­lectures and that professorial comments be restricted to Latin. The Thomistic fundamentals, or “capital theses,” were not to be “placed in the category of opinions capable of being debated one way or the other.”

A few weeks later, just before Pius X’s death, Cardinal Lorenzelli, prefect of the Sacred Congregation for Studies, published a list of twenty-four theses to be affirmed”including, at the very beginning, a statement of divine being as pure act, in contrast to the admixture of potency in creatures. In other words, these were metaphysical theses of just the sort that Pius X had said cannot be placed “in the category of opinions capable of being debated.” Everyone understood that Lorenzelli’s “XXIV Theses” were aimed in the direction of the sixteenth-century Jesuit scholastic philosopher Francisco Suárez, beginning with the doctrine of the real distinction between essence and existence in creatures, which was not generally held by his followers.

By the time Pius X died in 1914, the Vatican had in place two entirely different Thomisms, one broad and oriented to social questions, the other narrow and focused on capita that could not be debated. For a good example, look at the international congress in Granada that was planned for 1917, the third centenary of the death of Suárez. The Catholic press, of course, noted that the XXIV Theses had impeached the reliability of Suárez on certain questions of metaphysics. Moreover, the newly drafted Code of Canon Law (1917) required those in charge of religious and clerical formation to teach the “principles of the Angelic Doctor and hold to them religiously.” The congress did not fall under the discipline of canon law, but it was an awkward moment nonetheless, and Rome’s solution was to recommend that the congress focus on the social, political, and international-law aspects of Suárez’s thought. On these matters, one was permitted to avow an evolving line of thought and to celebrate its utility in handling modern problems.

And yet, beginning with Benedict XV, the papacy grew increasingly unwilling to enforce Pius X’s official Thomism, even within the seminaries and the religious orders. While the exhortations of Leo XIII and the ­precepts of Pius X were duly noted by Benedict and his successors, rigorous enforcement proved to be the exception rather than the rule. Indeed, only five months after Pius X’s death, Benedict said that there is room “for divergent opinions” so long as they constitute no “harm to faith or discipline” and so long as they are expressed “with due moderation.”

With the disaster of the First World War and the rise of the totalitarian regimes, the papacy’s attention was funneled back into the social and political issues. The shift of magisterial attention to political modernity is particularly evident during the pontificate of Pius XI, who became pope in 1922. In the 1923 encyclical ­ Studiorum Ducem , he approvingly quoted Pius X’s admonition that there must be no deviation from Thomas in metaphysical issues . This core of metaphysical systematics must be preserved intact, even while allowing the “lovers of Thomas” to engage in “honorable rivalry in a just and proper freedom which is the life-blood of studies.”

But what is most striking about Studiorum Ducem is the interest in the social and political issues. In Ubi Arcano (1922), Pius XI had insisted: “There is a species of moral, legal, and social modernism which We condemn, no less decidedly than We condemn theological modernism.” Accordingly, in Studiorum Ducem he emphasized Thomas’ contributions “in the science of morals, in sociology and law, by laying down sound principles of legal and social, commutative and distributive justice, and explaining the relations between justice and charity.” He noted particularly “those superb chapters in the second part of the Summa Theologiae on paternal or domestic government, the lawful power of the State or the nation, natural and international law, peace and war, justice and property, laws and the obedience they command, the duty of helping individual citizens in their need and cooperating with all to secure the prosperity of the State, both in the natural and the supernatural order.”

“It is therefore to be wished,” Pius XI concluded, “that the teachings of Aquinas, more particularly his exposition of international law and the laws governing the mutual relations of peoples, became more and more studied, for it contains the foundations of a genuine ‘League of Nations.’”

On paper, Thomas’ metaphysics remained the standard, but in practice Pius XI focused not on the prima pars , with its metaphysical armature, but rather the secunda pars of the Summa , on human conduct. While Pius XI never separated the two Thomisms”his encyclicals are as elegantly synthetic as were Leo’s”he focused intently, in the 1920s and 1930s, on Thomistic resources for the political and social problems.

Remember the four threads we set out to untangle in the last century and a half of papal teaching”the two Thomisms and the two Modernisms. On the one hand, there was a constructive and open form of Thomism, which began as a way to discuss political and social issues. On the other hand, there was a legislative and disciplinary form of Thomism, developed originally to discuss sacred doctrines and the metaphysical preambles to faith. Meanwhile, there were two ways to understand modernity: first, as a set of social and political problems brought to a head by the French Revolution and the loss of the Papal States; and, second, as a defiantly nationalist, antireligious, and anti-Catholic philosophical movement.

It would be convenient if the two pairs lined up in what appears to be their natural order: the disciplinary Thomism used for philosophical Modernism, and the constructive Thomism used for political modernity. Unfortunately, that was not always the case, and the two Thomisms and two Modernisms cannot be aligned in papal documents without a great deal of guesswork.

Still, the disciplinary form of Thomism may have created more problems than it solved, even when properly applied to matters of sacred doctrine. Lists of errors and truths never really achieved the results for which they were designed. Whether in response to political or philosophical modernity, the syllabi sparked confusions and resentments. In the news-­hungry environment of the modern media that emerged in the nineteenth century, these lists invited constant spin on the part of the Church’s friends and enemies. They did not substitute for a catechism, and they certainly did not equal the Leonine practice of encyclical teaching, which was more effective, both ad extra and ad intra .

Nor did the list-making approach play to the strong suit of Thomism, which requires not only definitions and conclusions but also a deeply textured set of questions and distinctions. The metaphysical issues were complex, subtle, and difficult on their own terms, never mind the practical questions of how to instantiate and enforce them in educational institutions. To put beyond debate the most intellectually challenging work of Thomas Aquinas did no favors for his ­heritage. A slight and passing familiarity with Thomas’ system, usually acquired secondhand and enforced as a party line, was almost bound to breed that kind of ­contempt that comes from bored students who know a little but not enough.

Ever since the French Revolution in 1789, the political and social questions have remained favorable terrain for the Thomists. In 2007, on the hundredth anniversary of Pius X’s anti-Modernist encyclical Pascendi Dominici Gregis , Peter Steinfels used his column in the New York Times to suggest that the encyclical was a “revival of the battle against liberalism that the papacy and much of the church had been waging throughout the nineteenth century”and tragically the purge the encyclical started crippled those very ­elements in European Catholicism that might have resisted the Church’s sympathy for authoritarian regimes after World War I, when liberal parliamentary governments were besieged by rising totalitarianism.”

Steinfels’ account is a common-enough reading of Catholic intellectual history, but we should, in fact, draw the opposite conclusion. The social and political vector of Catholic thought proved remarkably sturdy and successful, as though the Modernist controversy never happened. We often think of John XXIII’s Pacem in Terris (1963), with its long list of human rights, as the epitome of the Second Vatican Council’s spirit of aggiornamento . Of the twenty-five discrete rights listed in that encyclical, however, all but three are quotations or paraphrasings of Leo, Pius XI, and Pius XII. Moreover, by the time of Pacem in Terris , lay and clerical neo-Thomists”Maritain, Murray, Rommen, Journet, Simon”had produced a widely read body of scholarly literature on these subjects.

As ecclesiastical discipline declined precipitously in the 1950s and 1960s, systematic Thomism underwent a kind of defenestration. No longer privileged in the ­curriculum of either seminaries or Catholic schools, Thomistic metaphysics became a scholar’s specialty consigned to a chapter in the history of medieval ­philosophy. But we should not be surprised that in the topics related to human action”intention, choice, the moral virtues, natural law, and political philosophy”Thomism survived as worthy of study beyond the ­historical cubbyholes.

And yet the gradual separation of the social doctrine from the overall system of Thomas began to ­create the impression that the philosophy of practical reason was freestanding: a kind of first philosophy in its own right, connected to the metaphysical system and even sacred theology only by way of dotted lines. The two Thomisms ceased to be deeply integrated”with the secunda pars of the Summa Theologiae (on human action) read separately from the doctrine of providence, the metaphysics, and the anthropology of the prima pars . We need only survey the chronic and significant differences of opinion over the systematic grounding of natural law today, as well as the extraordinarily complicated and controversial skirmish lines over questions of moral theology, to see that this is so.

When he became pope in 1978, John Paul II inherited the problem of how to put the two Thomisms back together. As outward looking a pope as we have had since Leo XIII”as socially and politically concerned”John Paul II nonetheless saw that the solution required him to emphasize, throughout his pontificate, that Thomistic metaphysics demands study. Speaking at his alma mater, the Angelicum, on the anniversary of Aeterni Patris in 1979, he said that “the philosophy of St. Thomas is a philosophy of being, that is, of the ‘act of existing’ ( actus essendi ) whose transcendental value paves the most direct way to rise to the knowledge of subsisting Being and pure Act, namely to God.” In his 1998 encyclical Fides et Ratio , he again warned that theology needs both analytic rigor and a sapiential dimension drawn from a philosophy of being.

The real questions facing John Paul were, first, how to rekindle interest in sapiential philosophy without resorting to ecclesiastical imposition from on high, and, second, how to show its relevance to the practical problems. He found a solution that stood close to the genius of his magisterium. He contended in Fides et Ratio that anthropology is the nexus of the two Thomisms: “Metaphysics should not be seen as an alternative to anthropology, since it is metaphysics which makes it possible to ground the concept of ­personal dignity in virtue of their spiritual nature. In a special way, the person constitutes a privileged locus for the encounter with being, and hence with metaphysical enquiry.”

Far from conforming human persons to a philosophical system, the Church has held Thomas as the master because humans themselves thirst for the kind of wisdom Thomas pursued and taught. The metaphysical questions are neither divine nor angelic, but human ”because man himself stands at the frontier of matter and spirit. As John Paul II said: “The segmentation of knowledge, with its splintered approach to truth and consequent fragmentation of meaning, keeps people today from coming to an interior unity. How could the Church not be concerned by this? It is the Gospel which imposes this sapiential task directly upon her pastors.”

Some have claimed that, in all this, John Paul II is subordinating both human action and metaphysics to a philosophy of personalism, but that misjudges his steady desire to repristinate what Leo XIII had proposed in Aeterni Patris . We have come a long way from Pius X when John Paul II insists that the Angelic ­Doctor should also be called the Doctor Humanitatis . Thomas is recommended not as a tool for weeding out disorder within the Church but rather as a teacher on the integrity of the human person. There can be no social doctrine without reckoning with “the integral truth about what is real.” And there can be no efficacy in a systematic philosophy that loses sight of the vocation of the human knower to the whole of reality.

Russell Hittinger is the Warren Professor of Catholic Studies and research professor of law at the University of Tulsa.