The history of the Catholic Church is full of all sorts of heresies that have assailed the truths of the faith. From the earliest days of the Gnostics and Docetists all the way down to the Jansenists and Quietists of later centuries, it seems there has never been a shortage of heretical thought.
But in each age, God has brought forth bold and courageous men to combat each one. These warrior saints gave their life in service to Christ and His Church in their own way, either as martyrs, confessors, or simply as servants to others for the sake of the love of Jesus.
The following is a list of fifteen of the major heresies that the Church has faced, and the illustrious men who stood against them.
1. Pelagianism and St. Augustine of Hippo
“There is an opinion that calls for sharp and vehement resistance – I mean the belief that the power of the human will can of itself, without the help of God, either achieve perfect righteousness or advance steadily towards it.”1
Pelagianism radically corrupted the Church’s teachings on grace, sin, and the Fall. Its namesake, the British monk Pelagius (who was startled by some of the words of St. Augustine in his Confessions), taught that the sin of Adam had no bearing on subsequent generations; essentially, man was inherently good and unaffected by the Fall. In practice, this meant that a man could come to God by his own free will, no grace needed. Many saints fought against this doctrine – St. David of Wales stands out among them especially – but it was St. Augustine of Hippo, arguably the greatest of the Latin Doctors and “the Church’s mightiest champion against heresy”2, who rose to fight against this inherently venomous strand of thought.
Against Pelagius, St. Augustine upheld the truth that God’s grace is entirely necessary for any movement of ours towards God to occur at all. As he himself puts it, “We for our part assert that the human will is so divinely aided towards the doing of righteousness that, besides being created with the free choice of his will, and besides the teaching which instructs him how he ought to live, he receives also the Holy Spirit, through which there arises in his heart a delight in and love of that supreme and unchangeable Good which is God; and this arises even now, while he still walks by faith and not by sight.”3
2. Gnosticism and St. Irenaeus of Lyons
Gnosticism was arguably the biggest heresy of the early Church, a Hydra-like species of varying sects and figureheads that espoused all manner of profane mysticism, asceticism, and produced many false gospels. Among its central tenets was that Christ was merely a spiritual being, and not a flesh-and-blood man, that God the Father was actually a malevolent Demiurge, and that all matter was inherently evil.
The chief saint who fought Gnosticism, and dismantled all aspects of it was St. Irenaeus of Lyons. St. Irenaeus’ monumental work, Adversus Haereses, is a systematic account and refutation of every Gnostic sect presumably known by St. Irenaeus at the time. He tenaciously held that Christ was God in the flesh, for if Christ was merely a phantasm, then He did not suffer and die at all. His writing is essential for understanding the heresies that assaulted the Church in the first two centuries of its existence, as well as being an incredible account of apostolic tradition up to his time.
Aside from the various Gnostic sects that plagued the early Church, it is Arianism that is arguably the most famous of all Christian heresies. It struck at the very root and core of Christian teaching, that Jesus was God Himself in the flesh, and relegated the person of Jesus Christ to that of a mere created thing. It lives on today in varying forms, from well-known sects like the Jehovah’s Witnesses all the way to the bizarre world of Apollo Quiloboy; moreover, it still lurks within the sentences of some modern theologians who ambiguously state that Jesus is “the Christ” but no more than an exalted man.
St. Athanasius of Alexandria was the walking cure for this heresy. Stubborn and unshakeable, I think it not a stretch to say at times that this great man stood alone against wave after wave of Arian attacks on the truth of the Christian faith. By emphasizing and stubbornly holding to the truth of Christ as both God and man, St. Athanasius (along with others such as St. Hilary of Poitiers) effectively ended the reign of the Arian heresy within the Church.
4. Nestorianism and St. Cyril of Alexandria
St. Cyril of Alexandria was not known for his subtlety when it came to those who would attack the revealed truth of the Christian faith. When Nestorius arose on the scene, Pope St. Celestine I sent St. Cyril to quell the heresies spread by this man. Nestorius’ error was essentially (and might I say, ironically) two-fold: the Blessed Virgin Mary was not the Mother of God but merely the Christotokos (meaning “Christ-bearer”) and who also effectively claimed that Christ was really two persons accidentally united in one body (one divine, one human).
Against this, St. Cyril defended the unity of Christ’s person as both God and man with a ferocity that I have personally not witnessed in writing since St. Jerome defended the perpetual virginity of the Virgin Mary against Helvidius in 383 AD. St. Cyril’s brilliant defense of the person of Christ at the Council of Ephesus forever set up an impenetrable fortress against all those who would attack both the Incarnation and the Mother of God.
5. Monothelitism and St. Maximus the Confessor
Monothelitism declared that Christ had only one will (divine). Much like Monophysitism which had declared that Christ had only one nature (divine), Monothelitism is viewed by some as a compromise aimed at bringing Monophysites back to the Church. But by declaring that Christ had only a divine will, it amounted to little more than essentially stating that Jesus was not God in flesh but merely a human controlled by a divine will – Justin Holcomb of the Reformed website The Resurgence humorously describes it as “Jesus is controlled by Skynet”8.
Against this heresy arose the valiant St. Maximus the Confessor, who is to this day one of the most revered theological minds of the Christian East. His defense of the orthodox doctrine that Christ had both a human will and divine will was met with fearsome resistance – he ended up having his tongue torn out and his right hand cut off for refusing to acquiesce to the Monothelite Emperor Constans II, before being exiled and dying soon after.
6. Albigensianism and St. Dominic Guzman
“…his heart was well-nigh broken by the ravages of the Albigensian heresy, and his life was henceforth devoted to the conversion of heretics and the defence of the faith.”9
Gnosticism again reared its ugly head in the Middle Ages, this time in the form of what was known as Albigensianism. With its dualist worldview and inherent dislike for the Church due to corruption within her own ranks among the clergy, Albigensianism began to attract an incredibly large following, divided into the “perfect” and “believers.” Though often romanticized nowadays due to the revival of interest in Gnostic ideas and history within the New Age movement, from my point of view, it was anything but. In fact, it was alarming in its view of all matter as evil – suicide by starvation was encouraged among its members, in order to free the soul from the body. In fact, when a run-of-the-mill “believer” was given the spiritual baptism whilst seriously ill and/or dying, and happened to recover somehow, they were “as often as not smothered or starved to death (endura) in order to assure [their] salvation,”10 because only once could this ritual be performed.
Though the Cistercian order had been enlisted to combat this heresy, its success was minimal at best. St. Dominic instead founded the Order of Preachers, because in all practicality “what was needed was a new policy with missioners travelling in poverty, but well-equipped intellectually to deal with the errors in a charitable but effective way.”11 The accounts surrounding his battles against the heresy of the Cathari (as the Albigensians were also known) are incredible – his staying up all night in discussion with an Albigensian innkeeper in order to save his soul, the Virgin Mary’s arming him with the Holy Rosary, his singing hymns aloud along the roads where Cathari assassins lay in wait to murder him (much to their astonishment!), his only book that he carried being a copy of the Gospel of St. Matthew. It is even said of the Dominicans that “Our Lady took them under her special protection, and whispered to St. Dominic as he preached.”12
Though the murder of a papal legate by the Albigensians sparked a massacre in the form of the Albigensian Crusade, “Dominic himself took no part in the violence of the crusaders.”13 In the end, due to his zeal for, love of, and devotion to Christ, “he revived the the courage of the Catholic troops, led them to victory against overwhelming numbers, and finally crushed the heresy.”14
7. Latin Averroism and St. Thomas Aquinas
“This then is what we have written to destroy the error mentioned, using the arguments and teachings of the philosophers themselves, not the documents of faith. If anyone glorying in the name of false science wishes to say anything in reply to what we have written, let him not speak in corners nor to boys who cannot judge of such arduous matters, but reply to this in writing, if he dares. He will find that not only I, who am the least of men, but many others zealous for the truth, will resist his error and correct his ignorance.”15
One does not exactly hear of the movement known as Latin Averroism too much these days. But it was indeed a kind of heresy, if you will, a school of thought that attacked the truth of Christian dogma and belief at its core. Influenced by the Islamic philosopher Averroes (Ibn Rushd, labelled by the Scholastics as “the Commentator” due to his extensive commentaries on Aristotle), the Averroist Scholastics taught a kind of double truth. For the Averroist, something that was true in religion and theology could be at the same time false in philosophy and practicality. Mixed in with this paradoxical notion of “true and not true at the same time”, the Averroists also held that the world had always existed, and that there was only one collective soul in humanity.
Against this school of thought, St. Thomas Aquinas rose like a mighty fortress to protect Holy Mother Church. Instead of outright dismissing the thought of Aristotle like some (due to its being associated with this new movement in thought, as well as some of Aristotle’s ideas themselves), St. Thomas Aquinas answered the Averroists by using Aristotle himself. With precision and common sense, the Angelic Doctor pointed out the corruptions in the translations of Aristotle used by the Arab philosophers, corrected abuses of Aristotle’s thought, and harmonized faith and reason rather than separating them into two spheres of truth. All in a day’s work for one of the greatest minds the Church has ever known.
8. Calvinism and St. Francis de Sales
“In fact I thought that as you will receive no other law for your belief than that interpretation of the Scripture which seems to you the best, you would hear also the interpretation that I should bring, viz., that given by the Apostolic Roman Church, which hitherto you have not had except perverted and quite disfigured and adulterated by the enemy, who well knew that had you seen it in its purity, never would you have abandoned it.”16
In the inital aftermath of the Reformation, the varying schools of Protestantism had begun to take root. But none had shown themselves to be as staunch in resisting the Catholic faith as the followers of John Calvin. Though he makes extensive use of the thought of St. Augustine, he does so with hardly any reference to the rest of the Fathers (even a cursory glance at an index in a copy of his magnum opus, the Institutes of the Christian Religion, shows this), ignoring “all that Catholic foundation on which the Doctor of Grace built.”17
Enter St. Francis de Sales. Only 27 years old at the time, he was sent into one of the most anti-Catholic regions of all, the Chablais, wherein Calvinism had especially fortified itself. To do so was to invite being despised, rejected, misunderstood, threatened, and turned away. In many respects, St. Francis’ missions to the Calvinists call to mind the words of St. Paul himself – “I have been on frequent journeys, in dangers from rivers, dangers from robbers, dangers from my countrymen, dangers from the Gentiles, dangers in the city, dangers in the wilderness, dangers on the sea, dangers among false brethren; I have been in labor and hardship, through many sleepless nights, in hunger and thirst, often without food, in cold and exposure. Apart from such external things, there is the daily pressure on me of concern for all the churches. Who is weak without my being weak? Who is led into sin without my intense concern?” (2 Cor. 11:26-29)
With the Calvinist population staunchly refusing to listen to his words, St. Francis began to write and distribute pamphlets on the truth of the Catholic faith. These writings were compiled later on into one work, probably the greatest apologetic work against Protestant objections ever penned – Les Controverses. Known as “the gentleman saint”, St. Francis’ untiring love for souls (especially seen in his other great work, Introduction to the Devout Life), his knowledge of the faith and history, and his incredible ability to adapt and endure all manner of obstacles and hardship sent against him make him arguably the greatest of the Doctors who went forth against the errors of Calvinism.
9. Monophysitism and Pope St. Leo the Great
Monophysitism was essentially the opposite of the Nestorian heresy mentioned above; where Nestorius emphasized that in Christ “there was both a human hypostasis or person and a divine”19, the Monophysite heresy declared that Christ had only one nature, that His humanity was absorbed into His divinity. While the heresy of Nestorius was largely vanquished twenty years earlier by St. Cyril of Alexandria at the Council of Ephesus, it was Pope St. Leo the Great who arose to do battle with the heresy of Eutyches and the Monophysites.
Against Monophysitism, he taught the truth of the two natures of Christ (human and divine), saying of Christ that “we could not overcome the author of sin and death, unless He had taken our nature and made it his own…”20. “After three years of unceasing toil, Leo brought about its solemn condemnation by the Council of Chalcedon, the fathers all signing his tome, and exclaiming, ‘Peter hath spoken by Leo.'”21
10. Iconoclasm and St. John of Damascus
Iconoclasm, the rejection of the use of religious imagery in worship (icons, statuary, and even extending to the use of candles, incense, etc.) had a complicated history. In the early centuries, it was to be found amongst the heretical Paulician and Nestorian camps, but it was also espoused by some within the Church (including, very early on, St. Epiphanius of Salamis who “fell into some mistakes on certain occasions, which proceeded from zeal and simplicity.”23). Moreover, the heresy of Iconoclasm found much of its influence and fuel in the rise of Islam, which was fiercely opposed to the use of imagery in worship.
The chief heretic in this struggle was Emperor Leo II the Isaurian, who issued an edict forbidding the use of imagery in religious worship. St. John Damascene, considered the last of the Greek Fathers and the first of the Scholastics, immediately set to work defending the use of imagery by Christians since the earliest centuries of the Church. St. John was arrested by the Emperor, and (much like St. Maximus the Confessor) had his right hand severed as a punishment for his resistance to the heresy by way of his writings. Iconoclasm was eventually condemned by the Second Council of Nicaea in 787, but was resurrected again in the Protestant Reformation.
11. Jansenism and St. Alphonsus de Liguori
The errors of Calvinism were not only to be found within the Protestant realm, but within the Church too did they take root as well. This Catholic/Calvinist hybrid was founded by the theologian Cornelius Jansen, who, like Calvin, took the writings of St. Augustine and ran with them to the most extreme conclusions. A species of ridiculous moral rigorism and religious fear spread its shadows over the Church. It discouraged frequent Holy Communion, espoused a form of moral perfectionism as being arequirement to even receive the Eucharist at all. So successful was its influence that it even found adherents in such brilliant Catholic minds as Blaise Pascal.
Many great men and women stood firm against the pessimistic theology and destructive results of Jansenist doctrine, but it was St. Alphonsus de Liguori’s writings and thought which effectively sounded the death-knell of this particular form of heresy. Against the rigorism and fear espoused by Jansenism, St. Alphonsus encouraged frequent Holy Communion as a remedy for sin as long as one was not in a state of mortal sin, and developed a finely-tuned moral theology that became the standard textbook of all Catholic moral theology since. He is to this day not only revered as a Doctor of the Church and founder of the Redemptorist order, but as the most excellent of teachers on the subject of Catholic morality.
12. Brethren of the Free Spirit and Bl. John of Ruysbroeck
“This is that Wayless Being which all fervent interior spirits have chosen above all things, that dark stillness in which all lovers lose their way. If we could prepare ourselves through virtue in the ways I have shown, we would at once strip ourselves of our bodies and flow into the wild waves of the Sea, from which no creature could ever draw us back.”25
The heresy of the Brethren of the Free Spirit is not one that much heard of these days, but its influence is more widespread than is commonly known. Finding its beginnings in the Beguine and Beghard movement in the 13th and 14th centuries, this heretical movement found major inspiration in the sermons and writings of Meister Eckhart (though he himself denied any involvement with the movement). Emphasizing a form of indifference to salvation (a kind of proto-quietism), union with God in this life, and attacking the sacraments of the Church, this mystically-charged heresy began to spread itself all about central Europe.
Though some of the followers of Meister Eckhart himself (especially Bl. Henry Suso) either denied involvement with the Free Spirit movement and/or attempted to correct its teachings and combatted its influence with that of orthodox mysticism within the bounds of the Church, it was the greatest of the Flemish mystics, Bl. John of Ruysbroeck, that led the charge against this particular brand of mystical heresy.
The life of Bl. John is a fascinating one to peruse – spending much of his time in prayer and contemplation in the Sonian Forest near Groenendaal, his concern for the welfare of souls being led astray by the quietistic Free Spirit movement was such that he began to engage in open theological combat with them. His writings are some of the best ever penned on the Holy Trinity, as well as on the mystical life. Instead of writing linguistically remote treatises that could never be accessed by the average person at the time, Bl. John wrote many pamphlets in the vernacular that defended the faith against heretical attacks by such Free Spirit figureheads as Bloemardinne. By emphasizing the deepest aspects of mysticism within Church orthodoxy, he effectively brought about the end of this movement, though not without being persecuted intensely by adherents of this heresy.
13. Modernism and Pope St. Pius X
“That We make no delay in this matter is rendered necessary especially by the fact that the partisans of error are to be sought not only among the Church’s open enemies; they lie hid, a thing to be deeply deplored and feared, in her very bosom and heart, and are the more mischievous, the less conspicuously they appear. We allude, Venerable Brethren, to many who belong to the Catholic laity, nay, and this is far more lamentable, to the ranks of the priesthood itself, who, feigning a love for the Church, lacking the firm protection of philosophy and theology, nay more, thoroughly imbued with the poisonous doctrines taught by the enemies of the Church, and lost to all sense of modesty, vaunt themselves as reformers of the Church; and, forming more boldly into line of attack, assail all that is most sacred in the work of Christ, not sparing even the person of the Divine Redeemer, whom, with sacrilegious daring, they reduce to a simple, mere man.”26
Modernism is quite possibly the most controversial heresy mentioned on this list, because we are indeed, right up to this very moment, still in the throes of it. As for my own view, it seems to me to be the most ambiguous and chameleon-like of all heresies, and it can often be hard to pinpoint exactly where it is entrenched or where it has already passed through and damaged the faith.
Modernism seems to have had its beginnings, somewhat officially, in the 19th century. Figures such as Maurice Blondel, George Tyrrell, Alfred Loisy, Friedrich von Hugel and many others are considered major figures within the movement within the Catholic Church; in Protestantism, I would argue that much of it was to be found initially in the thought of Friedrich Schleiermacher.
The words of the modernist thinkers themselves is especially startling – Alfred Loisy wrote that “Christ has even less importance in my religion than he does in that of the liberal Protestants: for I attach little importance to the revelation of God the Father for which they honor Jesus. If I am anything in religion, it is more pantheist-positivist-humanitarian than Christian.”27
Its effects are highly destructive – central to it is the idea that the truths of the Christian religion must be subjected to Enlightenment-style rationalism, relativism and secularism. The truths of the ancient faith are viewed as outmoded, and consequently subjected to rigorous demythologization. Additionally, the notion of the evolution of dogma effectivelly brought to bear a devastating assault on the truths of the Christian religion.
The effects of a modernistic viewpoint are seen to this day in much theological thought, both Protestant and Catholic, in the writings of many major thinkers such as Hans Kung, Edward Schillebeeckx, Rudolf Bultmann, Karl Rahner, and a whole host of others. The status of whether many theologians and writers are actually modernistic is a hotly-debated topic.
On the Protestant end of it, it was resisted mightily by the Reformed theologian Karl Barth, especially in his clarion call against liberal theology entitled The Epistle to the Romans. Though beforehand, the Syllabus of Errors of 1864 and the encyclical of Pope Leo XIII entitled Providentissimus Deus had begun to defend the Church against Modernism, it was the great Pope St. Pius X who arose as the greatest defender of the Church by warning of modernism’s threat to the faith.
Calling it the “synthesis of all heresies”28, Pope St. Pius X released Lamentaboli Sane(Syllabus Condemning the Errors of the Modernist) and his monumental encyclical Pascendi Dominici Gregis against the modernist school of thought. Reading the work is a frightening wake-up call to the insidious nature of the heresy itself – unlike the dangerous yet frankly clumsy assaults of earlier heresies upon the faith such as Arianism and Montanism, Modernism was said to have infected the Church from the inside. One is reminded of a deadly illness more than an attack.
Pope St. Pius X also wrote the famed Oath Against Modernism which was required to be sworn to by clergy and others in the Church, and sought to warn the faithful before it was too late. Much work was done to extinguish modernist trends of thought within the Church thanks to this most venerable and saintly Pope, and to this day, he remains the most important saint to have ever fought against the poisonous infections of the movement.
14. Origenism and St. Methodius of Olympus
Without a doubt, the Alexandrian theologian Origen was the greatest mind of the early Church. Many of the great saints of the early Church were enthralled by his brilliance and his devotion – I would make mention of St. Basil the Great, St. Gregory Nazianzen, and St. John Cassian especially. Even St. Jerome, who became a bitter opponent of Origen’s thought later on, still held him to be one of the most admirable and brilliant minds the Church had yet known. St. Francis de Sales and St. Elizabeth Schonau, writing many centuries later, also spoke of his great services to the Church.
Nevertheless, some of the thought of Origen was exceedingly problematic. Being one of the first theologians proper of the early Church, he was prone to stumble when going too far deep into the truths of the faith. His tendency to over-allegorize, his teachings on the pre-existence of souls, amongst other things, ended up getting him into trouble later on.
But, in all fairness to Origen, there is a huge difference between the man and what later came to be known as “Origenism”. Origenism took latent elements in the experimental and speculative thought of Origen and often ran with it, much in the same manner, I would argue, as such men as John Calvin and Cornelius Jansen had done with the thought of St. Augustine.
Several saints began to criticize Origenism as such, notably St. Jerome and St. Epiphanius of Salamis. But the first to systematically attack the errors in Origen’s thought was one St. Methodius of Olympus. Himself well-trained in Platonist philosophy as well as the theology of the Church, St. Methodius vigorously critiqued the major errors in the thought of the great Alexandrian, including the eternity of the world and certain teachings of his on the resurrection. Though a devoted opponent of the thought of Origen, it is interesting to note that he still recognized his service to the Church.
The errors of Origenism were finally condemned at the Second Council of Constantinople in 553 AD, though The New Catholic Encyclopedia promulgated under the pontificate of Pope Pius XI says that “it is not proved that he incurred the anathema of the Church at the Fifth General Council.”
15. Religious Indifferentism and Pope Pius XI
“For union of Christians can only be promoted by promoting the return to the one true Church of Christ of those who are separated from it, for in the past they have unhappily left it. To the one true Church of Christ, we say, which is visible to all, and which is to remain, according to the will of its Author, exactly the same as He instituted it.”31
Religious indifferentism is, in essence, a kind of sub-species of modernism. It undermines the truth of the Catholic Church as the one true Church founded by Christ, and essentially states that it is a matter of indifference which church one belongs to. In many ways, it amounts to what might be termed “pan-Christianity”.
Against this notion, Pope Pius XI wrote the encyclical entitled Mortalium Animos, which again underlined that the Catholic Church was the Ark of Salvation, and attacked the idea of a kind of watered-down pan-Christian collective of churches. All that it amounts to, in essence, is a unity based upon false ecumenism, a kind of “whatever” pseudo-Christianity. This religious indifferentism essentially espouses the notion that “Controversies… and longstanding differences of opinion which keep asunder till the present day the members of the Christian family, must be entirely put aside, and from the remaining doctrines a common form of faith drawn up and proposed for belief, and in the profession of which all may not only know but feel that they are brothers.”32
Though many had condemned religious indifferentism beforehand (Pope Leo XIII, Pope Gregory XVI, Pope Benedict XV, as well as the 1864 Syllabus of Errors), it was Pope Pius XI who decisively defended the Church against it, quoting the early Church Father Lactantius: “The Catholic Church is alone in keeping the true worship. This is the fount of truth, this the house of Faith, this the temple of God: if any man enter not here, or if any man go forth from it, he is a stranger to the hope of life and salvation. Let none delude himself with obstinate wrangling. For life and salvation are here concerned, which will be lost and entirely destroyed, unless their interests are carefully and assiduously kept in mind.”33
1 – The Spirit and the Letter, IV
2 – Butler’s Lives of the Saints, “St. Augustine of Hippo”, 1894 edition
3 – The Spirit and the Letter, V
4 – Against the Heresies, IV:18:5
5 – On the Incarnation, VIII
6 – Second Letter to Succensus, I
7 – From here.
8 – From here.
9 – Butler’s Lives of the Saints, “St. Dominic”, 1894 edition
10 – Rev. John Laux, Church History, IV:1
11 – David Farmer, Oxford Dictionary of Saints, “Dominic”, pg. 146
12 – Butler’s Lives of the Saints, “St. Dominic”, 1894 edition
13 – David Farmer, Oxford Dictionary of Saints, “Dominic”, pg. 146
14 – ibid.
15 – De Unitate Intellectus Contra Averroistas, 124
16 – The Catholic Controversy, “Author’s General Introduction”
17 – William Barry, The Catholic Encyclopedia, “Calvinism”
18 – “Sermon 28”, VI
19 – The New Catholic Dictionary, “Monophysites and Monophysitism”
20 – Ep. xxviii, II
21 – Butler’s Lives of the Saints, “St. Leo the Great”, 1894 edition
22 – On Holy Images, I
23 – Butler’s Lives of the Saints, “St. Epiphanius of Salamis”, 1894 edition
24 – From here.
25 – The Spiritual Espousals, found here.
26 – Pascendi Dominici Gregis, 2
27 – Memoires II, pg. 397
28 – Pascendi Dominici Gregis, 39
29 – Concerning Free Will
30 – The New Catholic Encyclopedia, “Origenism”
31 – Mortalium Animos, 10
32 – ibid., 7
33 – Lactantius, Divine Institutes, IV:30:11-12, cf. Pope Pius XI, Mortalium Animos, 11