But though Islam rejected its philosopher, Averroës's work was by no means without its effect. It was through his commentaries on Aristotle that the thought of that greatest of ancient thinkers became known to the western world, both Jewish and Christian. Among the Jews, his writings soon acquired almost canonical authority. His system found expression in the works of the best known of Hebrew thinkers, Maimonides (1135-1204), "the second Moses" works which, despite all orthodox opposition, dominated Jewish thought for nearly three hundred years, and made the Jews during that time the chief promoters of rationalism. When Muslim persecution forced a large number of Jews to leave Spain and settle in Southern France, the works of Averroës and Maimonides were translated into Hebrew, which thenceforth became the vehicle of Jewish thought; and thus Muslim Aristotelianism came into direct contact with Christianity.
Among the Christians, the works of Averroës, translated by Michael Scott, "wizard of dreaded fame," Hermann the German, and others, acted at once like a mighty solvent. Heresy followed in their track, and shook the Church to her very foundations. Recognizing that her existence was at stake, she put forth all her power to crush the intruder. The Order of Preachers, initiated by St. Dominic of Calahorra (1170-1221), was founded; the Inquisition was legalized (about 1220). The writings of Aristotle and his Arab commentators were condemned to the flames (1209, 1215, 1231). Later, when all this proved unavailing, the best intellects in Christendom, such as Albertus Magnus (1193-1280), and Thomas Aquinas (1227-74), undertook to repel the new doctrine with its own weapons; that is, by submitting the thought of Aristotle and his Arab commentators to rational discussion. Thus was introduced the second or palmy period of Christian Scholasticism, whose chief industry, we may fairly say, was directed to the refutation of the two leading doctrines of Averroës. Aiming at this, Thomas Aquinas threw the whole dogmatic system of the Church into the forms of Aristotle, and thus produced that colossal system of theology which still prevails in the Roman Catholic world; witness the Encyclical Æterni Patris of Leo XIII., issued in 1879.
By the great thinkers of the thirteenth century, Averroës, though regarded as heretical and dangerous in religion, was looked up to as an able thinker, and the commentator par excellence; so much so that St. Thomas borrowed from him the very form of his own Commentaries, and Dante assigned him a distinguished place, beside Plato and Aristotle, in the limbo of ancient sages ('Inferno,' iv. 143). But in the following century--mainly, no doubt, because he was chosen as the patron of certain strongly heretical movements, such as those instigated by the arch-rationalist Frederic II--he came to be regarded as the precursor of Antichrist, if not that personage himself: being credited with the awful blasphemy of having spoken of the founders of the three current religions--Moses, Jesus, and Muhammad--as "the three impostors." Whatever truth there may be in this, so much is certain, that infidelity, in the sense of an utter disbelief in Christianity as a revealed religion, or in any sense specially true, dates from the thirteenth century, and is due in large measure to the influence of Averroës. Yet he was a great favorite with the Franciscans, and for a time exercised a profound influence on the universities of Paris and Oxford, finding a strong admirer even in Roger Bacon. His thought was also a powerful element in the mysticism of Meister Eckhart and his followers; a mysticism which incurred the censure of the Church.
Thus both the leading forms of heresy which characterized the thirteenth century--naturalism with its tendency to magic, astrology, alchemy, etc., etc., and mysticism with its dreams of beatific visions, its self-torture and its lawlessness (see Görres, 'Die Christliche Mystik')--were due largely to Averroës. In spite of this, his commentaries on Aristotle maintained their credit, their influence being greatest in the fourteenth century, when his doctrines were openly professed. After the invention of printing, they appeared in numberless editions,--several times in connection with the text of Aristotle. As the age of the Renaissance and of Protestantism approached, they gradually lost their prestige. The chief humanists, like Petrarch, as well as the chief reformers, were bitterly hostile to them. Nevertheless, they contributed important elements to both movements.
Averroism survived longest in Northern Italy, especially in the University of Padua, where it was professed until the seventeenth century, and where, as a doctrine hostile to supernaturalism, it paved the way for the study of nature and the rise of modern science. Thus Averroës may fairly be said to have had a share in every movement toward freedom, wise and unwise, for the last seven hundred years. In truth, free thought in Europe owes more to him than to any other man except Abélard. His last declared follower was the impetuous Lucilio Vanini, who was burned for atheism at Toulouse in 1619.
The best work on Averroës is Renan's 'Averroës et l'Averroïsme' (fourth edition, Paris, 1893). This contains, on pages 58-79, a complete list both of his commentaries and his original writings.