Stephen appears to link "Averroes and Moses Maimonides" because both of them sought to reconcile Aristotle's pagan Greek philosophy with revealed religion—Islam in Averroes' case, Judaism in Maimonides'.
Averroes (1126-98) was a Muslim philosopher and polymath in medieval Andalusia (Stephen has been thinking of the medieval "Moors") who wrote commentaries on most of Aristotle's works, which he read in Arabic translations. At the time when Averroes began writing, ancient Neoplatonic ideas had been incorporated into Christianity, but Aristotle had been largely forgotten. Averroes' commentaries on the Greek master's works exerted a powerful influence on Christian Scholastic philosophers, who extended the Averroistic synthesis of theism and Aristotelianism into their own religion. (Thomas Aquinas referred to Averroes simply, and reverently, as The Commentator. Aristotle was The Philosopher.) Gifford observes that "While he strove to reconcile Aristotle with Moslem orthodoxy (with heavy emphasis on God the Creator), he was suspected by the Moslem world of heterodoxy."
Maimonides (1135-1204) was a Jewish philosopher, rabbinical scholar, and physician. He was born in the same city as Averroes, Córdoba, nine years later, and lived in Morocco (where Averroes died) and Egypt. His 14-volume commentary on the Torah still is regarded as canonical, famed for its logical structure, its clarity, and its vast learning. A man of scientific intelligence, he also adapted Aristotelian thought to philosophizing about questions of faith. In this latter endeavor more than a whiff of heterodoxy attends him, just as it did Averroes. Many sophisticated Jews of early thirteenth century Spain and southern France were inspired by Maimonides' philosophy to reject traditional forms of belief and observance. For a discussion of this history, see D. J. Silver, Maimonidean Criticism and the Maimonidean Controversy, 1180-1240 (1965).
The paired figures of Averroes and Moses Maimonides return, very strangely, in Oxen of the Sun, when Stephen cites them as joint authorities on one of the circumstances under which women may become pregnant without intercourse. Gifford notes that Averroes did indeed write about the case history of a woman impregnated in her bath by a man bathing nearby, but that Maimonides has nothing to say on this topic.
Bloom thinks in Ithaca that Maimonides was a thinker of "such eminence that from Moses (of Egypt) to Moses (Mendelssohn) there arose none like Moses (Maimonides)."