Vetera Novis Augere et Perficere:Thomas Aquinas and Christian-Muslim Dialogue Joseph Ellul, O.P. Pope Leo XIII's encyclical letter Aeterni Patris, issued on August 4, 1879, sought to address many issues that were challenging nineteenth-century Catholic scholarship and academic life. In proposing the thought of Thomas Aquinas as a model of Catholic teaching, the Pope intended, in his own words, "to strengthen and complete the old by aid of the new,"1 not only by reviving the study of the works and teachings of the Angelic Doctor, especially in the realm of philosophy, but also to uphold as perennial his method of engaging with his contemporaries within and without the Catholic faith.2 It is within this context that we are called upon to reflect upon this appeal: "vetera novis augere et perficere." The thirteenth century was indeed a time of intellectual upheaval, following the introduction of Aristotle and, later on, the translations into Latin of the Arabic commentaries on Aristotle by Ibn Rušd (Lat. Averröes; d. 1198). This event was met within the ecclesiastical world with apprehension, if not outright fear. Neo-Platonic philosophy and its interpretation by Ibn Sina (Lat. Avicenna; d. 1037) was already perfectly acceptable to Mediaeval Christian scholars. The latter was in fact considered an essential tool for understanding the illuminationist thought of St. Augustine. Étienne Gilson even spoke of Augustinisme avicennisant (Avicennized [End Page 1231] Augustinianism).3 The problem was Aristotle and his renowned commentator Ibn Rušd: a pagan commented on by an infidel. One must also note, however, that mediaeval Western intellectuals and institutions were able to encounter and adapt the Islamic legacy, because they already possessed a sufficient scientific base (with of course the contribution of translations of Greek together with Latin works) with which to understand, assimilate, and build upon this new knowledge that appeared from the East. In sum, mediaeval Christendom created living, vibrant societies, constantly searching, always discovering something new. In dealing with the specific (and delicate) subject of Aquinas's dialogue with Islamic thought, it would be necessary to reflect in particular upon two key works of his: the Liber de Veritate Catholicae Fidei contra Errores Infidelium (A Book on the Truth of the Catholic Faith against the Errors of Unbelievers),4 popularly known as the Summa contra gentiles [SCG], together with his De rationibus fidei contra Saracenos, Gnæcos et Armenos ad Cantorem Antiochenum, better known simply as De rationibus fidei. At this point it would be necessary to articulate the term "Islamic thought." Of itself it should not be identified with Islam as a religion. Rather, it should be considered as embracing classical Greek philosophy as interpreted by the Neo-Platonic movement and disseminated through Oriental Christian and Jewish schools of thought. Islamic civilization absorbed these teachings and built its own proper ediice upon these foundations. A Model for Interreligious Dialogue? Proposing Thomas Aquinas as a model for engagement with Islamic thought may also raise a few eyebrows. Hence, it would be appropriate to pose an essential question: "What type of dialogue existed in mediaeval times?" One should begin with an a priori exclusion of dialogue as it is understood today, given the fact that there existed neither the motive nor the means to implement it. In fact mediaeval society was aware of only three religions: the pagan, which had been replaced by Christianity; the Jewish, founded upon the precepts of the First Covenant which "Christ fulilled by his actions and [End Page 1232] by his teaching"5 and which was also believed to prefigure the everlasting New Covenant sealed by Jesus on the Cross; and finally, the Christian, which believed in Jesus as the final revelation of God to humanity.6 With such a vision in mind it is obvious that any doctrine that is not situated within these parameters, or which proposes some form of belief or conduct which was different from, if not contrary to, the Christian vision of God, the cosmos, and society, would be considered as heretical and its promoter an impostor.7 When Islam made its appearance in the Christian world, it carried with it a book that it considered of divine provenance, and...