Siger de Brabant [Sighier, Sigieri Sygerius], French philosopher of the 13th century. About the facts of his life there has been much difference of opinion.

In 1266 he was attached to the Faculty of Arts in the University of Paris at the time when there was a great conflict between the four "nations." The papal legate decided in 1266 that Siger was the ringleader, and threatened him with death. During the succeeding ten years he wrote the six works which are ascribed to him and were published under his name by P 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.

In 1277 a general condemnation of Aristotelianism included a special clause directed against Boetius of Denmark and Siger of Brabant. Again Siger and Bernier de Nivelles were summoned to appear on a charge of heresy, especially in connexion 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 killed by an insane secretary (a clerico suo quasi dementi). 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 Martin IV was in residence at Orvieto.

In politics he held that good laws were better than good rulers, and criticised 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 as a persecuted philosopher.

See P Mandonnet, Siger de Brabant et l'Averroisme latin au xiiie Siècle (Fribourg, 1899); Gaston Paris, "Siger de Brabant" in La Poesie du moyen age (1895); and an article in the Revue de Paris (Sept. 1st, 1900).