Here’s what James Kiefer says about Aquinas:
In the thirteenth century, when Thomas Aquinas lived, the works of Aristotle, largely forgotten in Western Europe, began to be available again, partly from Eastern European sources and partly from Moslem Arab sources in Africa and Spain. These works offered a new and exciting way of looking at the world. Many enthusiastic students of Aristotle adopted him quite frankly as as an alternative to Christianity. The response of many Christians was to denounce Aristotle as an enemy of the Christian Faith. A third approach was that of those who tried to hold both Christian and Aristotelian views side by side with no attempt to reconcile the two. Aquinas had a fourth approach. While remaining a Christian, he immersed himself in the ideas of Aristotle, and then undertook to explain Christian ideas and beliefs in language that would make sense to disciples of Aristotle. At the time, this seemed like a very dangerous and radical idea, and Aquinas spent much of his life living on the edge of ecclesiastical approval. His success can be measured by the prevalence today of the notion that of course all Christian scholars in the Middle Ages were followers of Aristotle.
Aristotle is no longer the latest intellectual fashion, but Aquinas’s insistence that the Christian scholar must be prepared to meet other scholars on their own ground, to become familiar with their viewpoints, to argue from their premises, has been a permanent and valuable contribution to Christian thought.
Aquinas' vision of moral fulfillment as both a life of virtue and the intellectual love of God helped bridge the ancient Greek and Christian worlds in the history of Western religious and moral philosophy. In honor of Aquinas’ historic synthesis of Aristotelian philosophy and Augustinian theology, I offer below a section from my 1997 essay submitted for my “History of Ethics” qualifying exam at Vanderbilt University’s Graduate Department of Religion. The essay is entitled, “Moral Fulfillment and the Intellectual Love of God: Thomas Aquinas’ Reoccupation of Aristotle’s Theoria.”
In turning to Aquinas’ theory of moral fulfillment, it cannot be denied that more predecessors in the history of Western ethics influenced the treatment of the final end in the Summa Contra Gentiles and the Summa Theologiae than Aristotle. According to Vernon J. Bourke, Aquinas turned not only to Aristotle, but also to classical philosophy and the Church Fathers in constructing his ethics. Names as diverse as Plato, Epicurus, Zeno, Chrysippus, Philo, Plotinus, Porphyry, Simplicius, Cicero, Augustine, Boethius, and many others inform Aquinas’ thought. Nevertheless, it cannot be denied that Aristotle’s work exercises a pervasive and indelible influence on the ethics of Aquinas. A cursory examination of the Summa Contra Gentiles or the Summa Theologiae reveals references to Aristotle on virtually every page. It is no accident that Aquinas reserves the title “the Philosopher” for Aristotle alone.
Here is some of the context for Aquinas’ reception of Aristotle. Aquinas lived during a period in which Aristotle was, for all practical purposes, discovered in the West. But a long history of Aristotelianism fills the temporal distance between fourth century Greece and thirteenth century Europe. Around 50 or 40 B.C., Andronicus of Rhodes published Aristotle’s works, and by the third century Porphyry wrote a commentary on Aristotle’s Categories. Boethius made an early attempt to reconcile the philosophies of Plato and Aristotle in the sixth century. In fact, he was going to translate their works into Latin during an age in which knowledge of Greek was declining, but was executed for treason before he could complete the project. He did, however, finish translations of Aristotle’s Categories and On Interpretation, two “logical works that became the only Aristotle known at first hand in Europe before the twelfth century.” These translations insured the dominant influence of Aristotle’s logic on medieval thinkers, many of whom interpreted Aristotle under the influence of Platonism. Meanwhile, Arabic translations of Aristotle’s works in Syria captivated Islamic thinkers who preserved the writings and wrote commentaries on the works. Only by the twelfth and thirteenth centuries did the rest of Aristotle’s surviving works return to Europe from the Islamic world, reappearing in Spain and Sicily in Arabic and Hebrew translations. Over one hundred years later, reliable Greek texts finally appeared in Paris and Oxford.
The translation of these Greek texts into Latin prompted a philosophical “explosion of Aristotelianism.” Medieval Scholasticism retrieved Aristotle for various projects in creating “an encyclopedic synthesis of doctrines” which far transcend the scope of Aristotle’s original writings. Ancient and medieval proponents of Aristotelianism as diverse as Epicureans, Gnostics, Neoplatonists, Muslims, and Christians all attempted to appropriate Aristotle’s conception of the final good under various religious conceptions of salvation. Due largely to the influence of Platonism, Aristotle’s scientific inquiries served as springboards for various “‘metaphysical speculations.’”
At least six factors shaped the context in which thirteenth-century European theologians read the newly available works of Aristotle. First, the “effective history” of Aristotelianism outlined above established a precedent for appropriating Aristotle’s work for religious purposes which were foreign to the cultural and religious world of ancient Greece. If thirteenth century Christian theologians were to take Aristotle seriously at all, they would necessarily have to engage in the appropriation and “reoccupation” of Aristotle’s central concepts with specifically Christian theological meanings.
Related to the first factor is the second: the tradition of Augustinian Christianity provided much of the theological content which guided interest in and colored readings of Aristotle. Theological concepts like sin, grace, creation, redemption, heaven, and hell provided the hermeneutic lenses for reading the ancient philosopher. In the case of Aquinas, for example, the Augustinian views that “man in the concrete has a supernatural vocation,” that revelation is necessary for knowing that genuine happiness can be found only in God, that “grace is necessary even to begin to will to love God,” and that “moral perfection consists in loving God” constituted the theological prejudgments for receiving the ancient philosopher’s writings.
In addition, Alasdair MacIntyre notes that the Augustinian tradition parted from Aristotle in four additional ways: the “law of the polis” is ordered to the “law of the civitas Dei;” “the Augustinian catalogue of the virtues” expands to include “humility and charity,” both of which are alien to Aristotle’s conception of virtue; a new distinction between the good and the bad will informs the Aristotelian “psychology of reason, passion, and appetite;” and finally, the Augustinian moral cosmology strongly accents a conception of God as both “divine creator” and “divine lawgiver.” Particularly when viewed in light of this Augustinian legacy, one cannot legitimately say that Aquinas’ moral theology represents only an Aristotelian ethics any more than one can hold as adequate the view that Aquinas “merely ‘baptized’ Aristotle.” On this point, MacIntyre correctly argues that Aquinas’ achievement lies in reconciling two otherwise conflicting traditions of moral inquiry into a new synthetic unity which became the basis for a Thomistic tradition of moral inquiry.
Four additional historical factors play a role in shaping the context for Aquinas’ reception of Aristotle: the cultural memories of crusades, heresies, and inquisitions, as well as papal edicts banning public lectures on the works of Aristotle. Aquinas lived from roughly 1225 to 1274. According to historians, efforts in the eleventh and twelfth centuries to “build a unified Christian commonwealth” continued into the thirteenth century. Various heretical movements challenged this task, including groups like the Waldensians who were devoted to poverty and critical of the church hierarchy, and groups like the Albigensians who denied core church teachings about the sacraments and Christ’s divinity. After attempts at reconversion, Pope Innocent III decided that only a crusade against the Albigensians could effectively protect orthodox doctrine, and the infamous Papal Inquisition to root out heresy followed soon thereafter in 1231 under Pope Gregory IX.
When Aristotle’s writings surfaced and began exercising an influence on the thought and teaching in the universities, the context of reception was one concerned with orthodoxy versus heresy. Many voiced concerns about Aristotle’s philosophy as not only contrary to church teachings, but as a harmful influence on those entrusted with university education. According to Vernon Bourke, beginning around 1210 “several Councils forbade the teaching, either in public or private, of the works of Aristotle on natural philosophy,” although “the personal reading of Aristotle was not expressly forbidden.” And in 1231, Pope Gregory published an edict which stated that Aristotle’s “‘books of natural science which have been prohibited for a definite reason by a provincial Council may not be used at Paris, until they have been examined and all suspicion of error removed.’” Even the parts of the Nicomachean Ethics currently available were viewed with wariness.
Nevertheless, since the combined writings of Aristotle signaled “the greatest intellectual achievement known in the 13th Century,” they simply could not be ignored. The discovery of Aristotle’s thought, and the tendency to read Aristotle’s works as a coherent system of philosophy, posed a crisis of legitimacy for medieval Christian theology. After all, if a pagan philosopher can create such an intellectually coherent system of thought without recourse to revelation, then it appears that the need for Christian revelation and doctrine for insight into truth is called into question.
Aquinas believed that if anything in Aristotle’s works can be regarded as true, it can be useful for explicating the Christian faith. But if it were used in misguided ways, its truth could prove destructive for the integrity of Christian theology. Aquinas assumed the burden of mediating the tensions between orthodoxy and tradition on the one hand, and openness to philosophical and theological inquiry on the other. As a Christian theologian, Aquinas wanted to articulate and defend Christian teaching. He did not, however, want to see Christendom turn towards a dogmatic Christianity which upholds revelation at the expense of natural reason. Coming to terms with Aristotle was thus a challenge to properly mediate between an inherited Augustinian legacy and the new horizon of possibilities for systematic thought opened up by the discovery of Aristotle.
During Aquinas’ lifetime, no one fully established the legitimacy of Aristotle in the eyes of the orthodox. Suspicions continued to abound. Indeed, Aquinas himself was accused of heresy in 1270. According to his Dominican and Franciscan accusers, Aquinas held an unorthodox view on the relationship between the dead and the living body of Christ, mainly due to an extensive reliance on Aristotle. Given the fact that Aquinas’ accusers tended to side with the Pope in matters of doctrine, his theological views were read by his accusers as subverting legitimate authority. In his defense, Copleston notes that although Aquinas “did not hesitate to adopt an Aristotelian position even when this led him into conflict with traditional theories,” he also did not hesitate to reject aspects of Aristotle’s work “which were clearly incompatible with the Christian doctrine.” Vernon Bourke agrees, noting that Aquinas “was fully aware of the inadequacy of Greek ethics” even as he “used whatever he could find in the works of the Greek moralists” to support and clarify a Christian conception of moral fulfillment. Bourke cites Aquinas on this point:
And this is also clear: not one of the philosophers before the coming of Christ could with all his strivings, know as much about God and the things needed for eternal life, as would an old woman, by faith, after the coming of Christ.
After so many centuries of reading Aquinas as the “Angelic Doctor” and the epitome of orthodox Catholic theology, it is well to remember that his turn to Aristotle was a risky move and that, as a consequence, Aquinas was a radical theologian in his day.
 Warner Wick, “Aristotelianism,” in The Encyclopedia of Philosophy, Volume I, Paul Edwards, editor-in-chief (Macmillan, 1967), p. 149.
 Ibid., p. 150.
 Anthony Flew, A Dictionary of Philosophy, Revised Second Edition (St. Martin’s Press, 1979), p. 23.
 Wick, Op. cit., p. 150.
 The term “effective history” or “the principle of history of effect” is the English translation of German philosopher Hans Georg Gadamer’s Wirkungsgeschichte. It refers to the ongoing shaping power of past texts and traditions on any given present. See Hans Georg Gadamer, Truth and Method Second Revised Edition, translated by Joel Weinsheimer and Donald G. Marshall (Continuum, 1989), pp. 300ff.
 The term “reoccupation” is a metaphor used by Hans Blumenberg to describe the historical process of secularization in The Legitimacy of the Modern Age, translated by Robert M. Wallace (MIT Press, 1983). “Reoccupation” means that historical continuity is maintained over time in intellectual discourses insofar as new answer-positions come to occupy the function of former answer-positions within the historically inherited parameters of a discourse’s set of questions and answers. New answer-positions that successfully respond to the problems posed to as well as within an inherited set of questions and answers come to occupy the place of old answer positions when they can no longer maintain their legitimacy. Old answer-positions are structurally antecedent to new answer-positions, and new answer-positions “reoccupy” the “space” left vacant by the old answer-positions. Blumenberg’s theory of reoccupation accounts for historical continuity and change in intellectual history, as opposed to theories predicated on radical disjunctions, displacements, and epochal shifts.
 Frederick Copleston, A History of Philosophy, Volume II: Augustine to Scotus (Image Books, 1948), pp. 81, 83, & 84.
 Alasdair MacIntyre, Whose Justice? Which Rationality? (University of Notre Dame Press, 1988), pp. 162-163.
 Bourke, Op. cit., p. 12.
 MacIntyre, Op. cit., pp. 162-163.
 Mortimer Chambers, Raymond Grew, Barabara Hanwalt, David Herlihy, Theodore K. Rabb, and Isser Woloch, The Western Experience 4th Edition (Alfred A. Knopf, 1987), p. 337.
 Ibid., pp. 338-340.
 Bourke, Op. cit., p. 4.
 Ibid., pp. 4-5.
 Ibid., p. 5.
 Copleston, Op. cit., p. 429.
 Ibid., p. 431.
 Ibid., p. 426.
 Bourke, Op. cit., p. 42.