• Philosopher Sygerius de Brabantia, 1240
  

Little is known about many of the details of his life. In 1266 he was attached to the Faculty of Arts in the University of Paris at the time when a riot erupted between the French and Picard "nations" of students — a series of loosely organized fraternities. The papal legate threatened Siger with execution as the ringleader of the Picard attack on the French, but no further action was taken. During the succeeding 10 years, he wrote the six works which are ascribed to him and were published under his name by Pierre Mandonnet in 1899. The titles of these treatises are:

• De anima intellectiva (1270);
• Quaestiones logicales;
• Quaestiones naturales;
• De aeternitate mundi;
• Quaestio utrum haec sit vera: Homo est animal nullo homine existente;
• Impossibilia.

In 1271 he was once more involved in a party struggle. The minority among the "nations" chose him as rector in opposition to the elected candidate, Aubri de Rheims. For three years the strife continued, and was probably based on the opposition between the Averroists, Siger and Pierre Dubois, and the more orthodox schoolmen. The matter was settled by the Papal Legate, Simon de Brion, afterwards Pope Martin IV. Siger retired from Paris to Liège.

Averroism was controversial because it taught Aristotle in its original form with no reconciliation with Christian belief. Siger was accused of teaching "double truth" -- that is, saying one thing could be true through reason, and that the opposite could be true through faith. Because Siger was a scholastic, he probably did not teach double truths but tried to find reconciliations between faith and reason.

In 1277 a general condemnation of Aristotelianism included a special clause directed against Boetius of Dacia and Siger of Brabant. Again Siger and Bernier de Nivelles were summoned to appear on a charge of heresy, especially in connection with the Impossibilia, where the existence of God is discussed. It appears, however, that Siger and Boetius fled to Italy and, according to John Peckham, archbishop of Canterbury, perished miserably.

The manner of Siger's death, which occurred at Orvieto, is not known. A Brabantine chronicle says that he was stabbed by an insane secretary (a clerico suo quasi dementi). The secretary is said to have used a pen as the murder weapon and his critics claimed since he had done so much damage with his pen, he deserved what was coming. Dante, in the Paradiso (x.134-6), says that he found "death slow in coming," and some have concluded that this indicates death by suicide. A 13th century sonnet by one Durante (xcii.9-14) says that he was executed at Orvieto: "a ghiado it fe' morire a gran dolore, Nella corte di Roma ad Orbivieto." The date of this may have been 1283 - 1284 when Pope Martin IV was in residence at Orvieto. His fellow radicals were lying low in the face of the Condemnations of 1277 and there was no investigation into his murder.

In politics he held that good laws were better than good rulers, and criticized papal infallibility in temporal affairs. The importance of Siger in philosophy lies in his acceptance of Averroism in its entirety, which drew upon him the opposition of Albertus Magnus and Aquinas.

In December 1270 Averroism was condemned by ecclesiastical authority, and during his whole life Siger was exposed to persecution both from the Church and from purely philosophic opponents. In view of this, it is curious that Dante should place him in Paradise at the side of Aquinas and Isidore of Seville. Probably Dante knew of him only from the chronicler than as a persecuted philosopher.