Averroës (c. 1126–c. 1198) was born into a prominent family of lawyers and judges and was himself trained as a lawyer in both civil and religious affairs. He traveled from Córdoba to Marrakesh in 1153 and decided that Aristotle had been correct in stating that the world was round when he was able to observe Canope, a star not visible in Spain. He served as both advisor and doctor to the sultan of Marrakesh, who encouraged a series of commentaries on Aristotle. His writings include treatises on medicine and astronomy, but he is best known for his The Incoherence of Incoherence, which was a reply to al-Gazali’s (1058–1111) The Incoherence of the Philosophers. In his Incoherence of Incoherence, Averroës defended natural reason as a means to attain knowledge in all domains. By natural reason Averroës, and others after him, meant ordinary thought processes rather than religious intuition or revelation.

Averroës also wrote a set of commentaries on Aristotle that was influential in Western medieval scholarship. When his interpretations of Aristotle did not square with his own assumptions, he wrote detailed “supplements” of his own. For example, Aristotle’s Physics and On the Heavens were composed as two separate works and based on different types of observations. Under Plato’s influence, Averroës assumed that they were united.