Siger of Brabant lived in the medieval era, a time when Western learning was almost extinguished by the social and political dissolution which enveloped Europe in the aftermath of the collapse of the Western Roman Empire. Every bit of scholarly work produced by philosophers in the 13th century came under the intense scrutiny of the Catholic Church, and there was not much tolerance when it came to philosophical developments outside of what the powerful Church deemed copasetic with Catholic theology. Historians often pit Siger of Brabant’s work against the work of Thomas Aquinas, who tried to mash Aristotle’s views concerning the universe into a Christian framework. Aristotle's writings were of paramount importance to many Medieval philosophers, including Siger of Brabant, who once said “I say that Aristotle competed the sciences, because none who followed him up…has been able to add anything to his writings…Aristotle is a divine being.”
Siger of Brabant’s ideas concerning Aristotle were affected primarily by the philosophy of Averroes, an influential Muslim thinker. Averroes's work inspired the philosophical subset of Aristotelianism, the Latin Averroeists, a group with which Siger de Brabant afilliated strongly. Similarly to Aquinas, Averroes worked on specific interpretations of Aristotle that integrated his teachings on the forces of nature with his faith. While he made an effort to develop a school of thought that incorporated both Muslim thought and Aristotelian views, he primarily sought to separate religion from philosophy. Through removing the need to reconcile everything one believes about the intellectual world with what one believes in a spiritual sense, Averroes thought reason would better coincide with his philosophical endeavors. Philosophy, Averroes argues, was worthy enough of a goal to pursue on its own merits, rather than as a prop to hold up various points of theology. Therefore while both Averroes and Aquinas tied Aristotle’s views of the physical world to their respective faiths, Averroes believed something could be true in respect to philosophy but not true when it came to religion. Siger of Brabant stated “We have nothing to do with the miracles of God, since we treat things in a natural way.” Because of this embrace of conflicting notions, Latin Averroists had no problem accepting Aristotle’s eternity of matter doctrines. Because all matter is eternal, according to both Aristotle and Averroes, Siger of Brabant rejected the Christian story of creation.
Siger of Brabant’s interpretations of Aristotle focused on the possibility of a single immortal soul shared by humans everywhere, rather than an individual immortal soul. Concerning the very nature of the soul, Siger of Brabant references Aristotle’s work De Anima I, in which Aristotle sets forth that because the soul, specifically the intellective soul, exists apart from the physical world, it must not have the same quantifiable traits as the rest of physical matter. Because of this aspect of the soul’s makeup, Siger of Brabant argues that the soul cannot belong to an individual, as this would lead to multitudes of souls, reproducing new souls with the generation of new flesh. Averroes’ influence concerning the importance of faith surfaces when he discusses the possibility for a single human intellect. Because Aristotle is not clear on the subject, Siger of Brabant suggests that one must “hold fast to the faith, which surpasses human reasoning.” Latin Averroists, despite their emphasis on reason, ultimately believed spiritual revelation the most important guide when pursuing the truth.