This chapter examines the life of Jesus of Nazareth and how his teachings, style of life, and legacy shaped western thought. Emphasizing Jesus as both a historical figure and a moral exemplar, it explores how early followers remembered him and how later premodern readers interpreted him through close readings of the New Testament. Drawing especially on the Gospel of Mark and the Sermon on the Mount in Matthew, the chapter shows how Jesus gained authority not through institutional power but through humility, parables, miraculous acts, and a radical ethical vision. He preached inward sincerity over outward ritual, taught that all people possess dignity in the eyes of God, and urged his followers to model their lives on his own. Key themes include divine justice, the challenge of wealth and status, and the contrast between worldly and heavenly authority. Jesus emerges as a moral teacher, healer, and disruptor of conventional hierarchies. His parables and aphorisms – especially those in the Sermon on the Mount – became foundational to Christian ethics. The chapter concludes by noting how Jesus’ model of life and speech created a movement that profoundly transformed the cultural and moral framework of the West.

The Epilogue situates the close of late antiquity and the rise of Islam within a broader narrative of continuity, exchange, and transformation. It opens with Gregory the Great’s reflections on unity and diversity in the Christian Church, marking the culmination of the late antique synthesis of faith, philosophy, and governance. From there, it turns eastward to the origins of Islam, recounting Muhammad’s revelatory experience and the early spread of a faith that would, within a century, unite vast territories from Arabia to Spain and Central Asia. The emergence of Islamic centers of learning—Baghdad, Bukhara, Samarkand—revived Greek philosophy in Arabic translation and interpretation, producing thinkers such as Al-Kindi, Al-Farabi, Avicenna, and Averroes, whose reconciling of faith and reason later informed the scholastic debates of the Latin West. The chapter closes with a return to Europe and to figures like the twelfth-century scribe Guda, whose self-portrait in a manuscript reminds us that women, too, shaped medieval intellectual life. Across these worlds, the Epilogue underscores that “Western” thought has always been the product of conversation—between Greeks, Romans, Jews, Christians, and Muslims; between men and women; between faith and reason.

One of the central themes of this book is that, contrary to usual treatments, Arnauld has a consistent and subtle method and that once this method is appreciated the consistency of his philosophical thought emerges. Chapter 2 plays a central role in that overall argument by offering an account of Arnauld’s method and basic epistemological commitments. I argue that Arnauld distinguishes between three sources of knowledge - the central two being faith and reason - and each has a distinctive method for its use. I continue to outline Arnauld’s general rationalist commitments concerning reason. Finally, I argue for a central, and overlooked, difference between Arnauld’s and Descartes’s epistemological commitments revolving around their respective uses of clear and distinct ideas and accounts of judgment. This difference allows Arnauld to endorse many of the aspects of Descartes’s rationalism, while maintaining stricter limits on the scope of such knowledge.

Chapter 1 has three main topics: the structure and aims of the Summa theologiae, faith and reason, and the type of demonstration Aquinas uses in the Five Ways. First, there is a look at the divisions of the Summa into (three) Parts, Treatises, Questions, and Articles. The articles are structured like a debate. The work’s Prologue suggests that Aquinas writes for students of theology but he well knows that his experienced peers in the Church and universities are interested in his theological positions. The chapter then treats his views on faith and reason, mainly in Summa theologiae Ia q.1. It looks at the nature of “sacred teaching” (sacra doctrina). A central theme is how Aquinas sees the legitimate findings of human reason as compatible with revelation, rightly interpreted. Finally, the chapter explains how Aquinas settles on a certain method of demonstrating God’s existence, called a demonstration “quia” or “that” God exists.

The term “grace” refers to unmerited gifts of God, among which might be gifts of knowledge. Does God offer knowledge over and above what we could have learned just through the still earlier gift of our inbuilt reasoning powers? At stake is the authenticity of the deeds, and the truth of the teachings, recorded in Holy Scripture. Thomas Aquinas always takes natural reason as far as he can before turning to what God has revealed by grace; he wants us to trust Revelation, but only authentic Revelation. Now, though, he turns the inquiry around. In order to know all that we need to know about God, do we need His grace at all? This inquiry amplifies the one in Question 1, Article 1.

It would hardly be persuasive for St. Thomas to say that we need divine Revelation just because divine Revelation tells us so. He does quote from Holy Scripture to show that it confirms his conclusions, but the argument in this Article is based squarely on reason: we need Revelation because some of the things we need to know cannot be found out by reason alone, and because even many of those things which can be are very difficult for reason to ascertain.

We saw at the outset of the book that Thomas Aquinas considers reason a preamble to faith. But to faith in what? Human life is triply haunted, by the specter of absurdity, by the burden of brokenness and guilt, and by the dread of mortality and incompleteness. Can there be meaning, can there be healing and forgiveness, can we be everlastingly fulfilled? According to St. Thomas, the answers to these three questions are provided in the Gospel of Jesus Christ, who bore our sins and opened the path to the Father. This scandalizes us because if the Gospel is true, then the facile and comforting proposal of “many roads to heaven” is false. It scandalizes us even more because it asks something of us. And so the Treatise on the One God is not the end of our investigation, but the beginning.

Philosophy, magic and Scripture are not capable of leading men to the knowledge of truth. According to Pseudo-Clement, truth is revealed only by the True Prophet, because he alone possesses full knowledge of it. Anyone can recognise the True Prophet, provided that they are animated by a genuine desire to know the truth and that they meet a genuine witness. The witness does not prove the truth of the doctrine that he teaches, but he puts the hearers in the presence of the One from whom he has himself received the truth. Truth – though rationally arguable – is not conceptual knowledge, but evidence derived from the encounter, mediated by authentic witnesses, between the seeker and the Prophet.

The continuity of the Christian faith with classical philosophy is one of the common variables to Augustine’s three earliest dialogues. Augustine is particularly interested in the relation between faith and reason or, more precisely, the relation between Christian auctoritas and reason. This chapter contends that Augustine does not conceive of authority and reason as two diverse paths of ascent, but as distinct elements that comprise one integrated path of ascent. For Augustine, authority and reason are coordinate means of ascent to wisdom and happiness. The dialectal character of authority and reason operate in tandem to purify and enlighten the soul for the ascent to God. In the dialogues, it is the role of reason to offer an intellectus fidei, an intellectual account of the mysteries delivered by authority.

This chapter first offers an overview of key concepts in The Sickness unto Death, such as human nature, self, despair, and wholeheartedness. It then discusses the relation between Part One and Part Two of The Sickness unto Death, offering a comparison of different types of despair (or doublemindedness). In this connection, it discusses the relations between faith and reason, and philosophy and theology. It is argued that the relatively neglected Part Two of The Sickness unto Death, entitled “Despair is Sin,” reinterprets the problem of despair from Part One by introducing the Christian concept of sin. In Part Two, sin represents an unwillingness to be oneself before God that involves self-deception. Overcoming despair, on the other hand, requires an unconditional will to be oneself before God. However, the latter does not accept everything as it is but rather hopes against hope to reconcile ideals with reality. For Kierkegaard, this hope is interconnected with Christian faith, charity, and moral commitment. Indeed, overcoming despair by forming a wholehearted or coherent self represents a fundamental moral and religious task according to Kierkegaard.

Chapter 6, which is the last chapter, considers the importance and contemporary relevance of Thomas’s understanding of the virtues in light of what has been established in the previous chapters. The virtues are not basic to Thomas’s understanding of moral goodness in the way that they are in some contemporary versions of virtue ethics. Nevertheless, they are needed to organize and account for the various ways of living a full life. Contemporary sciences might add precision or material to Thomas’s account, but it is not clear that they require radical changes to it.

Thomas Aquinas, the most important theologian of the medieval Latin Church, receives ample treatment in this chapter. It covers his understanding of theology, God’s existence and God-talk, theology of the Trinity, the theological virtues and salvation.

After a brief survey of his life, this chapter examines the theology of St. Augustine, focusing on his views on faith and reason, theology of the Trinity and the psychological analogy, salvation, and spirituality (frui and uti).

The thought of Ockham represents a watershed in medieval theology. Ockham is often seen as the father of nominalism, and his epistemology, views on faith and reason, theology and philosophy, are duly examined.

By discussing different interpretations, Chapter 12 shows that Kierkegaard is a suprarationalist, who takes faith to be above reason, not against it. Specifically, he is neither an irrationalist, who takes faith to be irrational, nor an antirationalist, who claims that faith and reason oppose each other, without any logical contradiction or irrationality. Indeed, for Kierkegaard, faith seems capable of overcoming the hostility and antagonism between faith and reason that antirationalism emphasizes. Still, Kierkegaard’s nonreligious pseudonyms do contrast faith and reason in order to counteract theological views that are overly rationalistic and scientific. Indeed, Kierkegaard goes as far as criticizing the Augustinian idea of faith seeking understanding. But instead of promoting blind faith, he attacks rationalist and intellectualist accounts of faith that do not do justice to the mysteries of divine revelation and the incarnation. He therefore maintains that faith cannot be reduced to conceptual understanding, although it must nevertheless both involve and seek practical understanding.

Chapter 10 shows that Kierkegaard develops his views on faith and reason by using classical German philosophy from Leibniz to Kant. Specifically, he develops the much-discussed category of the leap by making creative use of Jacobi and Lessing. The result is an original account of the leap relevant to both philosophy of religion and more general debates concerning rationality, incommensurability, and noncommensurability. Specifically, the “leap” concerns both general transitions between different normative standards and religious conversions in particular. Even when different standards diverge and conflict, such leaps need not be blind or irrational, if one abandons standards that collapse internally, and the new standards hold up. This general approach allows Kierkegaard to sketch a Kantian reductio of religious nonbelief. However, he appears to follow Schelling in taking Kant’s critique of the ontological argument for God’s existence to show that being is not a predicate, and that thought and being, possibility and actuality, are therefore heterogeneous. Whether or not something exists is then a contingent matter that cannot be known a priori.

By examining little-known primary sources that are largely untranslated, Chapter 11 examines whether religious faith is absurd or irrational for Kierkegaard. It is shown that Kierkegaard was familiar with the irrationalist reading of his work as developed by his forgotten contemporary Magnús Eiríksson in the book Is Faith a Paradox and “By Virtue of the Absurd”? (1850). More importantly, Kierkegaard’s (drafted) reply to Eiríksson is clear that faith is only seemingly absurd and irrational, something that undermines the irrationalist reading of him considerably. Still, faith does seem absurd to nonbelievers since it provokes and scandalizes our understanding. Nevertheless, Kierkegaard argues that faith overcomes this absurdity and offense. Finally, his neglected reply to Eiríksson sheds light on his much-discussed use of pseudonyms and the relation between Fear and Trembling and Concluding Unscientific Postscript in particular.