Siger of Brabant

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Siger of Brabant (c. 1240–1284) was a master in the Faculty of Arts at the University of Paris and the most visible figure in the controversy over how far a Christian philosopher could follow Aristotle. He read the Greek philosopher through the commentaries of the Andalusian Averroes, and pressed the readings where they led — into open conflict with the teachings of the Church. For that he became, in his own century and after, the standing example of reason taken too far.

Siger of Brabant (upper right, in red) among the wise spirits of the Heaven of the Sun, in a fifteenth-century illuminated manuscript of Dante’s Divine Comedy (MS Thott 411.2) — Royal Danish Library, via Wikimedia Commons (public domain).

A canon in the Street of Straw

He came out of the Duchy of Brabant, in the Low Countries, around 1240, and like many ambitious clerics of the region was drawn to Paris, where the arts faculty had become the busiest school in Latin Christendom. He held a benefice as a canon of Saint-Paul in Liège — a secular cleric, not a friar bound to an order — and by the early 1260s was a regent master, lecturing for a hire in the Rue du Fouarre, the Latin Quarter street that the city named for the straw the students sat on and that Dante would later render as the Vico de li Strami, the Street of Straw.

The Rue du Fouarre in the Latin Quarter of Paris, the medieval Street of Straw where masters such as Siger lectured on Aristotle to students seated on straw — Mu, via Wikimedia Commons (CC BY-SA 3.0).

The arts faculty was, in the formal order of the medieval university, the preparatory faculty: its masters taught the seven liberal arts and the philosophy of Aristotle to young men who might pass on to theology, law, or medicine. In practice the arts masters had become something more dangerous than a propaedeutic. They had the whole recovered Aristotle in their hands, freshly translated and freshly glossed, and a growing conviction that philosophy was a discipline with its own object and its own authority, answerable to its texts and its proofs rather than to the theologians upstairs.

Siger was a leader among them, and a contentious one. As early as 1266 the papal legate Simon of Brion — the future Pope Martin IV — named him as the head of a turbulent faction in the faculty during the disputes that split the masters into warring nations; in 1271 he was again at the center of a quarrel, this time over the election of the university rector. The man who emerges from the records is less a serene metaphysician than a combative academic at the head of a party, teaching at the high edge of what the arts faculty was permitted to teach.

What a faithful reading of Aristotle required

Bust of Aristotle, a Roman marble copy after a Greek bronze by Lysippos, in the Palazzo Altemps, Rome; the recovered works of Aristotle were the ground of the controversy — Jastrow, via Wikimedia Commons (public domain).

The trouble lay in what a strict reading of Aristotle seemed to demand. Two conclusions in particular followed from the text and broke against Christian doctrine. The first was that the world had no beginning in time but was eternal — that motion and matter had always been, with no first moment of creation. The second, and the more explosive, concerned the intellect. On the reading Averroes had given of the third book of Aristotle’s On the Soul, the rational intellect was not a faculty multiplied in each person but a single separate substance, numerically one, in which all human beings participate. There is one mind, shared; individual men are joined to it only for the span of an act of thought, in what the schoolmen called an operative union. From this the hardest consequence followed: if the intellect is one and separate, then it is not what dies when a body dies, and nothing personal — no individual rational soul, no remembering self — survives death at all.

Both conclusions sat inside a cosmology the Latin West had inherited from the Arabic philosophers, and which descended in turn from Neoplatonism behind Plato. In the schemes of Avicenna and al-Farabi, reality unfolds by emanation: from the First a graded series of separate Intelligences proceeds, each governing a celestial sphere, down to the lowest of them, the Agent Intellect, which stands over the sublunar world. That separate Agent Intellect, not a power lodged in the individual, is what illuminates the human mind and lifts its knowing from potency to act — the way light makes a latent color visible. Averroes pushed the architecture one step further by making the receptive, possible intellect separate and single as well, so that both poles of human thought lay outside the individual person. Siger took the structure over on Averroes’s terms. The intellect that thinks in a man is not, on this reading, strictly his own.

He did not state these as articles of faith. His characteristic move, at least in the earlier work, was to set out what philosophy concludes — the intention of Aristotle and his commentators, what reason demonstrates when it follows its own texts to the end — while granting that the faith holds otherwise and that the faith is true. The world’s eternity is what the natural philosopher, reasoning as a natural philosopher, is driven to; that the world was created in time is what a Christian knows. The task he set himself was to report the one without denying the other.

The double-truth charge

Later readers compressed this into the accusation of a “double truth” — the claim that one and the same thing could be true in philosophy and false in theology at once, two contradictory truths held in two hands. Modern scholarship treats that label warily. It was largely a polemical coinage fixed on the Paris arts masters by their opponents rather than a thesis any of them defended in those words, and the surviving texts read less as a brazen embrace of contradiction than as a careful, sometimes uneasy, marking of the boundary of what unaided reason can reach. The arts masters were qualifying the scope of a demonstration — what follows if one reasons strictly within natural philosophy — not asserting that reason and revelation deliver rival truths of equal standing. The same posture runs through the work of Siger’s close contemporary in the faculty, Boethius of Dacia, whose treatise on the eternity of the world makes the qualification explicit. Whether Siger held it sincerely or as a shield against the censors is exactly the question that has divided his readers ever since.

Siger against Aquinas

Thomas Aquinas confounding Averroes, who lies overcome at his feet; tempera and gold on panel by Giovanni di Paolo, c. 1445–50, Saint Louis Art Museum — via Wikimedia Commons (public domain).

The recovered Aristotle was the common ground of the age, which is why the quarrel cut so deep: it set the arts faculty against the Dominican theologian who was, in those same years, reading Aristotle to opposite ends. Thomas Aquinas held that the intellect is the substantial form of the individual human being — that each person has his own rational soul, which informs his body and is the seat of his own thought, and which can subsist after death as that person’s soul. Against the unicity of the intellect he wrote, at Paris in 1270, the treatise De unitate intellectus contra Averroistas — On the Unity of the Intellect, Against the Averroists — a direct and unusually sharp polemic whose target, though Siger is not named, is the doctrine he and his circle were teaching. Its argument turned the Averroist reading back on itself: if the intellect were one and separate, it would not be this man who understands, and the plain fact that this man thinks his own thoughts would be unaccountable. The two men became the fixed poles of the central question of the age — whether the mind that knows is the person’s own, and whether the person endures. Aquinas’s reply survives intact and is the sharpest documentary witness to the controversy; its full text shows him meeting the Averroist reading of Aristotle line by line on its own ground.

The pressure told. After 1270 Siger appears to have tempered his position. In the disputed questions on the Metaphysics and in a now-lost treatise on the intellect, he moves toward something closer to Aquinas: the intellective soul, he allows, is bound to the human cogitative power in such a way that it is multiplied and individuated, and can be called the form of the man — and God, not a created sphere-intelligence, is named the Agent Intellect. The trajectory is the heart of a long scholarly dispute. Fernand Van Steenberghen, in Maître Siger de Brabant (1977), the work that organized a century of study of the man, read this as genuine philosophical development by a sincere Christian whose late position lay near Aquinas’s own; an older line of interpretation, associated with Pierre Mandonnet, held instead that Siger was the strictest of Averroists who never truly recanted and merely trimmed his sails. The texts are reportationes — students’ records of lectures — and ambiguous enough to sustain both readings.

The condemnations

The institution did not wait on the philosophers to settle it. In December 1270 the bishop of Paris, Étienne Tempier, condemned thirteen propositions of the kind the arts masters were teaching: the unicity of the intellect, the eternity of the world, the denial that the personal soul is the form of the body, the denial of divine providence over individuals, the denial of human free choice. In November 1276 the Inquisitor of France, Simon du Val, cited Siger by name for heresy, and he left Paris. In March 1277 Tempier issued a far longer and more sweeping list — two hundred and nineteen condemned propositions, a disciplinary dragnet that caught not only the Averroists but, in places, positions held by Aquinas himself, who had died three years before. A specific process accompanied the act against Siger and against Boethius of Dacia. The 1277 condemnation became one of the most consequential interventions of the medieval Church in the life of the schools: it hardened the line between what philosophy might argue and what the faith required, and its long aftershocks reach into the work of later masters such as Duns Scotus, who had to philosophize in its shadow. The pattern of the whole controversy — the arts faculty pressing Aristotle to the edge, the theologians of the mendicant orders, Bonaventure among the Franciscans and the school of Alexander of Hales behind him, pressing back — is the frame in which all of high scholasticism in the Middle Ages defined itself.

The texts and the scholarship

The recovery of Siger as a thinker rather than a heresiarch is the work of the modern critical editions. Bernardo Bazán’s Louvain edition of the Quaestiones in tertium de anima, the De anima intellectiva, and the De aeternitate mundi (1972) put the core treatises on a secure textual footing for the first time; the disputed questions on the Metaphysics survive in several student reportationes — the Munich, Vienna, Cambridge, and Paris records — edited by William Dunphy and Armand Maurer, and it is from these that the late, softened positions are read. Much of the older corpus once labeled Siger’s has been doubted or reassigned in the course of this editorial work. Around the texts stands the great interpretive divide: Fernand Van Steenberghen’s Maître Siger de Brabant (1977) made the case for genuine development toward Aquinas against Pierre Mandonnet’s earlier portrait of an unrepentant Averroist, and the dispute over which Siger is the real one has not closed. The wider setting — how the graded Intelligences, the separate Agent Intellect, and the unicity doctrine passed from the Arabic falsafa into the Paris schools — is laid out in the scholarship on the Arabic and Islamic influence on the Latin West; the parallel method of his condemned colleague, who qualified what holds “speaking as a natural philosopher” against what is true absolutely, is set out in the study of Boethius of Dacia, the clearest evidence that the “double truth” charge was a frame imposed from outside rather than a banner the arts masters raised themselves.

Orvieto, and Dante

Having left France, Siger went to the papal court, then at Orvieto, whose tribunal had a name for greater leniency than the inquisitors at home. There he was kept under a kind of house surveillance, in the company of a cleric, and there, sometime in the pontificate of Martin IV — the same Simon of Brion who had once denounced him as a young firebrand — he died. The accounts agree on a violent end and little else: a Brabantine chronicle reports that the cleric who attended him, in a fit of madness, stabbed him to death. A letter of the English Franciscan John Peckham, dated 10 November 1284, speaks of him as already dead. The circumstances are uncertain and the sources do not agree, but the broad shape is fixed: a Paris master who had argued the world eternal and the soul not his own, dead by a deranged hand at the gate of the Church he had unsettled.

What keeps his name lit is a poet. In the tenth canto of the Paradiso, among the luminous spirits who wheel in the Heaven of the Sun, it is Aquinas himself — Dante’s own theological master — who points Siger out, the eternal light of Sigier, who, lecturing in the Street of Straw, syllogized invidious truths. That a poem steeped in Thomism should set the Averroist beside Aquinas, and in glory, and have Aquinas be the one to praise him, has been read in many ways: as a gesture of reconciliation across the great quarrel, as honor paid to intellectual rigor whatever its conclusions, as a deliberate puzzle the poet meant to leave sharp. The adjective Dante chose — invidïosi, the truths that drew envy or that were grudged him — has itself been argued over for centuries, and no reading has closed the case. It is one of the reasons a relatively obscure university teacher, whose own books were scattered, kept a name.

Siger left commentaries and disputed questions rather than a finished system, and much of what was once attributed to him is now doubted or reassigned among the critical editions. He survives less as a body of doctrine than as a position: the point at which the recovered Aristotle strained against revelation hard enough that the institution moved to hold them apart, and a faculty of philosophers learned, at his expense, exactly where the edge of their authority had been drawn.

→ Related: Alexander Of Hales · Middle Ages · Aristotle · Averroes · Avicenna · Al Farabi · Thomas Aquinas · Neoplatonism · Plato · Scholasticism · Bonaventure · Duns Scotus · Giordano Bruno · Emanation · Soul