Medieval Christian Philosophy

Medieval Christian philosophy is the thought of the Latin West, and of its Greek-speaking neighbour Byzantium, from the last century of the Roman Empire to around 1400. Its thinkers were almost all clergy or monks, and most of them would have called themselves theologians. Yet over these thousand years they built a tradition of argument as rigorous as any before it, asking whether God's existence can be proved, how universal ideas relate to particular things, whether the world had a beginning, what makes a human being one individual, and how far unaided reason can go before it needs revelation.

The period is often caricatured as an age of faith in which philosophy stood still. In fact it was an age of recovery and translation. It began with a handful of Latin books salvaged from the ancient world and ended with universities from Paris to Kraków teaching almost the whole of Aristotle, much of it reached through Arabic commentators. That story links this era tightly to Islamic and Jewish philosophy, which ran alongside it, and it leads directly into the humanism of Renaissance philosophy.

The tradition begins in the late Roman Empire, where Christianity had become the official religion and educated Christians had to decide what to do with pagan learning. The Greek schools described in Hellenistic and Roman philosophy were still active, and the most influential of them in this period was Neoplatonism, the system of Plotinus, who taught that all reality flows from a single, utterly simple source, the One, and that the soul's task is to turn back towards it.

Augustine of Hippo (354–430) was the decisive figure. Born in Roman North Africa, he passed through Manichaean dualism and scepticism before reading "the books of the Platonists" in Milan and converting to Christianity in 386. Neoplatonism gave him a way to think of God as immaterial and of evil not as a substance in its own right but as a lack or privation of good. In the Confessions, written from 397, he turned his own life into a philosophical inquiry into memory, desire and time, arguing that time exists only in the mind's stretching between memory and expectation. Against the sceptics he argued that one cannot be deceived about one's own existence, since to be deceived one must exist, an argument that anticipates Descartes by twelve centuries.

Augustine's theory of knowledge held that the mind grasps unchanging truths, such as those of mathematics, only because God illuminates it, much as the sun lets the eye see. His City of God, prompted by the Visigothic sack of Rome in 410, contrasted the earthly city built on love of self with the heavenly city built on love of God, and denied that any empire, Rome included, carried divine destiny. His later writings against the Pelagians, who held that people can choose the good by their own effort, stressed original sin and the priority of divine grace. For the next eight hundred years Augustine was the main authority after Scripture, and almost every later debate about free will, knowledge and the soul began from his texts.

As the Western Roman Empire dissolved in the fifth century (see the fall of Rome), knowledge of Greek faded in the Latin West. Boethius (c. 480–524), a Roman aristocrat serving the Ostrogothic king Theodoric in Italy, planned to translate all of Plato and Aristotle into Latin and show that they agreed. He finished only part of Aristotle's logic, together with Porphyry's Introduction to it, but those translations and his commentaries were almost the only Aristotle the West possessed for six hundred years. A remark in his commentary on Porphyry, asking whether genera and species exist in reality or only in the mind, set the agenda for the medieval debate over universals.

Accused of treason, Boethius wrote The Consolation of Philosophy in prison before his execution. In it Lady Philosophy explains that fortune is by nature unstable, that true happiness lies in the highest good, which is God, and that God's foreknowledge does not destroy human freedom because God sees all time at once in an eternal present, rather than predicting events in advance. The book was among the most copied and translated texts of the Middle Ages.

Around the same time, in 529, the emperor Justinian I barred pagans from teaching. The Neoplatonic school at Athens closed, though teaching continued for a time at Alexandria, where Christian and pagan commentators on Aristotle worked side by side. Two other sixth-century Latin writers, Cassiodorus and Isidore of Seville, compiled encyclopaedic handbooks that preserved fragments of ancient learning in monastery libraries.

In the Byzantine Empire, Greek remained the language of learning, so the original texts of Plato and Aristotle never had to be recovered. Byzantine thinkers worked mostly within theology. A Syrian writer of around 500, who presented himself as Dionysius the Areopagite, the convert of Paul the Apostle, combined Christian teaching with the Neoplatonism of Proclus. He described God as beyond all names, so that the truest statements about God are denials, and pictured the universe as a hierarchy of angels and churches through which divine light descends. Accepted as apostolic for a thousand years, these writings had enormous authority in both East and West. Maximus the Confessor in the seventh century and John of Damascus in the eighth systematised Greek Christian doctrine, and John's summary of the faith later reached the West in Latin.

In Constantinople, the scholar Photios in the ninth century and Michael Psellos in the eleventh revived the study of ancient philosophy. Psellos taught Plato and the Neoplatonists so enthusiastically that his pupil John Italos was condemned in 1082 for applying philosophical reasoning to doctrine. In the fourteenth century the Hesychast controversy pitted Gregory Palamas, who defended the monks' claim to experience God's uncreated energies through prayer, against critics trained in Latin-style argument; Palamas's position became Orthodox teaching. Byzantine scholars such as Gemistos Plethon later brought Greek manuscripts and Platonic enthusiasm to Italy, especially to Florence, shortly before the fall of Constantinople in 1453.

In the Latin West, learning revived under Charlemagne, whose Carolingian Empire needed literate clergy and administrators. Scholars such as Alcuin of York organised cathedral and monastery schools and standardised the copying of books. The curriculum rested on the seven liberal arts: the trivium of grammar, rhetoric and logic, and the quadrivium of arithmetic, geometry, music and astronomy.

The most original thinker of the age was John Scottus Eriugena (c. 800–c. 877), an Irishman from Ireland who taught at the court of Charles the Bald, king of West Francia. He was one of very few westerners of his time who read Greek, and he translated Pseudo-Dionysius and Maximus the Confessor into Latin. His great dialogue, the Periphyseon (On the Division of Nature, c. 862–867), divided all reality into four: nature that creates and is not created (God as source), nature that is created and creates (the primordial causes or ideas), nature that is created and does not create (the world of things), and nature that neither creates nor is created (God as the end to which all things return). The scheme pictured the universe as an outflowing from God and a homecoming. Eriugena also insisted that true reason and true authority cannot conflict. His views were later felt to blur the line between God and creation, and the Periphyseon was condemned in 1210 and 1225.

After the disruptions of the ninth and tenth centuries, the schools recovered in the eleventh. Logic, or dialectic, became a fashion, and some theologians feared that reasoning about the Eucharist and the Trinity would undermine faith. Anselm of Canterbury (1033–1109), an Italian who became abbot of Bec in Normandy and then archbishop of Canterbury in the Kingdom of England, showed instead how reason could serve faith. His motto was faith seeking understanding: he believed first, but wanted to understand what he believed by argument alone, without appeal to Scripture.

In the Proslogion (1077–1078) he offered what Kant would later call the ontological argument. God is that than which nothing greater can be conceived. Even someone who denies God understands this description, so God exists at least in the mind. But a being that existed in reality as well as in the mind would be greater than one existing only in the mind. So if God existed only in the mind, one could conceive something greater than that than which nothing greater can be conceived, which is a contradiction. Therefore God exists in reality. A monk named Gaunilo replied at once that the same reasoning would prove the existence of a perfect island, and philosophers have argued over the proof ever since. Anselm's Why God Became Man gave a rational account of the incarnation, and he is often called the father of scholasticism.

The twelfth century was a time of growing towns, trade and population, of the Crusades, and of a scholarly boom centred on the cathedral schools of northern France. Chartres was known for Platonist cosmology drawn from a Latin fragment of Plato's Timaeus, and Paris attracted students from across Europe to its masters on the Left Bank.

The most brilliant and combative of these masters was Peter Abelard (1079–1142). He defeated his teachers in public debate, and his affair with his student Heloise, their secret marriage and his castration by her relatives made him notorious; their later letters are among the best-known texts of the Middle Ages. On universals, Abelard rejected both the view that a universal such as "human" is a real thing shared by all humans and the view that it is a mere spoken sound. Universals, he argued, are words that signify by referring to a real likeness between individuals, a "status" of being human, without being things themselves. In ethics he located moral worth in a person's intention or consent rather than in the outward act. His Sic et Non (Yes and No) set side by side apparently contradictory statements of the Church Fathers on 158 questions, inviting readers to resolve them by careful analysis of language. Bernard of Clairvaux saw this as arrogance, and Abelard was condemned at Soissons in 1121 and again at Sens in 1141.

His method nonetheless won. Peter Lombard's Sentences (c. 1155) organised the opinions of the Fathers on God, creation, Christ and the sacraments into a systematic textbook, and for three centuries every theologian made his name by lecturing on it.

Around 1200 the masters and students of Paris organised themselves into a guild, a universitas, recognised by king and pope; Oxford followed, and Bologna in Italy was already famous for law. Later foundations spread across the continent, including Naples (1224), Prague (1348), Kraków (1364) and Vienna (1365). Students began in the arts faculty, studying logic and natural philosophy for several years, before moving on to the higher faculties of theology, law or medicine.

The teaching style that developed there is called scholasticism. Its basic unit was the question. A master posed a question, such as whether the world is eternal, listed the arguments on one side, cited an authority for the other, gave his own answer, and then replied to each opposing argument in turn. Regular public disputations, including free-for-all sessions in which anyone could raise any question, tested masters in front of their colleagues. The method was slow and technical, but it forced writers to state objections fairly and to define their terms with great precision.

What transformed the universities was a flood of newly translated texts. In the twelfth century, scholars working in Toledo, which had passed to the Christian kingdoms during the Reconquista, and in Norman Sicily around Palermo, translated Greek science and philosophy from Arabic. Gerard of Cremona alone produced dozens of versions, and Dominicus Gundissalinus, working with Jewish collaborators, translated Avicenna and al-Ghazali. Others, such as James of Venice, worked directly from Greek manuscripts obtained in Byzantium. By about 1200 most of Aristotle's works on nature, the soul and metaphysics were available in Latin, along with Arabic commentaries. From the 1220s Michael Scot translated the long commentaries of Averroes, whom the Latins simply called the Commentator, and later in the century William of Moerbeke made more literal translations from the Greek. Jewish thought arrived too: the Guide of the Perplexed of Maimonides was read in Latin by the 1240s.

This new Aristotle was exciting and alarming. He offered a complete account of nature, of the soul and of ethics built without revelation, and parts of it clashed with Christian teaching: he held that the world had no beginning, and his account of the intellect, especially as Averroes read it, seemed to leave no room for personal immortality. A Paris synod banned lectures on Aristotle's natural philosophy in 1210, and the ban was repeated in 1215, but it was never effective elsewhere and quietly lapsed. By 1255 the Paris arts faculty required nearly the whole Aristotelian corpus.

The new religious orders of friars, the Dominicans and Franciscans, founded in the early thirteenth century, soon supplied the leading theologians. The Dominican Albert the Great, who taught at Paris and Cologne, commented on almost all of Aristotle and encouraged the study of nature. His student Thomas Aquinas (1225–1274), from a noble family near Naples, became the most influential of all scholastics.

Aquinas held that reason and faith are distinct but cannot truly conflict, since both come from God. Reason working from the senses can prove that God exists, and his Five Ways argue from motion, causation, contingency, degrees of perfection and the order of nature to a first mover, first cause and necessary being. Other truths, such as the Trinity, are known only by revelation. Following Aristotle, he taught that the human soul is the form of the body, not a separate being trapped inside it, yet argued that the intellect's activity shows the soul can survive death. He distinguished between what a thing is, its essence, and the fact that it is, its existence: in every creature these differ, while in God alone they are identical. His ethics combined Aristotle's virtues with Christian charity and grounded human law in a natural law that reason can discover. The unfinished Summa Theologiae, begun around 1265, remains the best-known product of the age. Aquinas was challenged in his lifetime and some of his positions were caught up in the condemnations at Paris, but he was canonised in 1323 and later became the official doctor of the Catholic Church.

His Franciscan contemporary Bonaventure (c. 1217–1274), minister general of his order, was more cautious. He used Aristotle, but his thought remained Augustinian: all true knowledge depends on divine illumination, philosophy left on its own falls into error, and he argued that a world without a beginning is self-contradictory. His Journey of the Mind into God describes a climb through creation, the soul and the divine names towards mystical union.

Some masters of arts at Paris, notably Siger of Brabant and Boethius of Dacia, taught Aristotle as Averroes read him and accepted that philosophy, followed strictly, reaches conclusions contrary to faith, such as an eternal world and a single intellect shared by all humans. Their opponents accused them of holding a "double truth", one for philosophy and another for faith, though they never quite said that. In 1270 Stephen Tempier, bishop of Paris, condemned thirteen propositions. On 7 March 1277, after a papal inquiry, he condemned 219, ranging from the eternity of the world and the unity of the intellect to claims that God could not make several worlds or move the heavens in a straight line. Anyone who taught them faced excommunication. Eleven days later Robert Kilwardby, archbishop of Canterbury, issued a separate condemnation at Oxford.

Tempier named no one, and only a portion of the propositions can be traced to known texts. Historians still debate the significance of the event. The physicist Pierre Duhem once claimed it gave birth to modern science by freeing thinkers to imagine possibilities that Aristotle had ruled out, such as a vacuum; few scholars now accept that strong a version. What is clear is that after 1277 theologians laid new stress on God's absolute power and freedom, and that the confident synthesis of Aristotle and Christianity was replaced by more critical approaches.

The Franciscan John Duns Scotus (c. 1265–1308), from Scotland, taught at Oxford, Paris and Cologne and was nicknamed the Subtle Doctor. Against Aquinas, who held that words such as "good" apply to God only by analogy, Scotus argued that some concepts, above all "being", apply to God and creatures in exactly the same sense, though God possesses them infinitely; otherwise, he reasoned, natural knowledge of God would be impossible. He explained what makes each individual unique through a principle he called haecceity, or "thisness", which distinguishes Socrates from every other human being. He gave the will priority over the intellect, so that a free choice is not simply settled by what the mind judges best.

William of Ockham (c. 1287–1347), an English Franciscan, went further. He denied that universals exist outside the mind at all: only individual things exist, and general terms are signs in the mind that stand for many individuals. This position, nominalism, came with a principle of economy known as Ockham's razor, the rule that one should not multiply entities beyond necessity. Ockham developed a sophisticated logic of terms and stressed that God, being omnipotent, could do anything that involves no contradiction, so the order of nature is contingent rather than necessary. Summoned to the papal court at Avignon on suspicion of heresy, he fled in 1328 with the head of his order during the dispute over Franciscan poverty and spent his last years under the protection of the emperor Louis IV in Munich, in the Holy Roman Empire, writing against papal claims to temporal power. Political philosophy flourished in such conflicts: Marsilius of Padua's Defender of the Peace (1324) argued that authority in the Church and the state derives from the community.

In the decades after Ockham, Paris and Oxford produced remarkable work in logic and natural philosophy. The Oxford Calculators at Merton College analysed motion and change mathematically, while at Paris Jean Buridan developed the theory of impetus, the idea that a thrown body moves because the thrower has impressed a force on it, and Nicole Oresme discussed whether the Earth might rotate daily. John Wyclif at Oxford attacked church wealth and some doctrines, and his ideas influenced Jan Hus in Prague and, later, the Protestant Reformation. In the Rhineland, Meister Eckhart preached a mystical theology of the soul's union with God and was posthumously condemned in 1329.

These developments took place against the Black Death, which killed many masters and students after 1347, the Hundred Years' War between the Kingdom of France and England, and the papal schism that began in 1378. By about 1400 a different intellectual style was emerging in Italy. Petrarch had already mocked the scholastics' jargon and their reverence for Aristotle, and the poet Dante Alighieri had folded scholastic philosophy into a vernacular epic. The humanists of the Renaissance preferred classical Latin, Cicero and, increasingly, Plato. Scholasticism did not vanish; it continued in universities, among Spanish theologians and in Catholic and Protestant schools well into the seventeenth century, and figures of early modern philosophy such as Descartes were trained in it.

Medieval philosophers left a lasting inheritance. They refined logic and the analysis of language far beyond their ancient sources. They formulated arguments for God's existence that are still debated, and posed the problem of universals in a form that runs through later metaphysics. Their discussions of natural law, intention and the limits of political power fed into later theories of rights. And through their translators they connected the Latin West to the Greek and Arabic worlds, so that Aristotle reached Aquinas partly through readers in Baghdad, Bukhara and Córdoba. For the wider story of philosophy across eras and continents, see the history of philosophy.