In his much discussed lecture at Regensburg University on September 12, 2006, Pope Benedict underscored the crucial importance of Hellenistic philosophy in the development of early Christian theology. That engagement with philosophy is indeed of lasting importance for Christian theology. It is grounded not only in the teaching about the universal logos found in the Gospel of John, which was rightly emphasized by Benedict, but also in the thought of the apostle Paul. It is true that Paul had harsh words for the “worldly wisdom” that rejected the message of the crucified and risen Son of God. But he also affirmed that, by the exercise of clear reason, human beings know of the one God”the one God who is creator of the world and who revealed himself in Jesus Christ, as proclaimed by the apostles. (See Romans 1 and 2, and Acts 17.)

Greek philosophy was in search of the true nature of the divine, which led to the conclusion that there can be only one God. The one God of the People of Israel, however, who was also the God of Jesus and the early Christians, was viewed by the Greeks as an alien deity of an alien people and so could not command their allegiance. It was therefore necessary to make the argument that the God of Israel is, in fact, the one God conceived by the philosophers. This contention was essential to the plausibility of both Jewish and Christian witness in the Hellenic world.

For Christian theology, making this claim about the identity of the one God was not just an early instance of cultural adaptation”a cultural adaptation that could, in different times and different places, be succeeded and replaced by other forms of “inculturation.” The affirmation that the God of Israel and the God of the philosophers is the one and same God”an affirmation that entails the reception by Christian theology of the philosophical argument for the one true God”is a constitutive and permanent feature of Christian faith.

This is by no means a peculiarly Roman Catholic understanding. In his large catechism, Martin Luther says that God the Father, as proclaimed by Jesus, is the only true God “because nobody else could create heaven and earth.” In this he is entirely in accord with early Christian thinkers and their use of philosophical theology. To be sure, Luther was sharply critical of what he viewed as the dominance of Aristotle in Scholastic theology, but he did not reject the entire tradition of Christianity’s incorporation of Greek philosophy. He did not, for instance, reject Platonism, which, we do well to remember, had been the primary influence in Christian theology until the thirteenth century and again since the Renaissance. Luther was not alone in questioning whether the Aristotelian metaphysics mediated through Muslim commentators such as Averroës could be reconciled with a Christian understanding of God the creator. That question was much disputed prior to Albert the Great and Thomas Aquinas and would be disputed again after the death of Thomas in 1274.

Recall, too, that the earlier Augustinian tradition of Scholastic theology was no less committed to a positive engagement with philosophical reasoning than was the Aristotelian. Moreover, in later Protestant theology, largely due to the influence of Philip Melanchthon, Luther’s closest collaborator, the use of Aristotelian metaphysics was restored and had an important place until the early eighteenth century. Nor did the rise of modern philosophy lead to the abandonment of the synthesis of philosophical and theological thought, at least not in all cases. Schelling and Hegel, for instance, were notable advocates of the substantial unity of faith and reason.

The call for the “dehellenizing” of Christian theology, which Pope Benedict so sharply criticizes, arose in Protestant theology toward the end of the nineteenth century as part of a broader campaign against “metaphysics.” Metaphysics was depicted as philosophical baggage from the past that must now give way to “positive science.” It was with Albrecht Ritschl (1822-1889) and his school that the cause of dehellenizing Christianity appeared, and it was later given powerful support by the historian Adolf von Harnack (1851-1930).

Viewed in perspective, however, the program of dehellenizing Christian thought was not a lasting movement in modern Protestant theology. Aristotle may not have fared well, but the Platonic-Augustinian tradition remains strong. As for the larger question of the relationship between faith and reason, the philosophical and theological connections were hardly abandoned after the impact of Cartesianism. One thinks, for instance, of British empiricism in the line of John Locke, of German idealism in its several expressions, of American projects aimed at the development of an evolutionary theology, of the experimentalism of William James, and of the school of process theology associated with the philosophy of Alfred North Whitehead.

As for metaphysics itself, the claim that it has been rejected by modern thought has come in for increasing criticism. When did the supposed end of metaphysics occur? Auguste Comte (1798-1857), who coined the term sociology, confidently declared that metaphysics died with the rise of natural science. Wilhelm Dilthey (1833-1911), on the other hand, contended that the modern sense of history killed metaphysics. An awareness of historical contingencies and the relativity of our own ways of reasoning, he and others claimed, precluded metaphysical claims to absolute and definitive truth. What most attacks on metaphysics had in common was the rejection of rational theology.

Closer to our own time, Martin Heidegger also proclaimed the death of metaphysics, arguing that it happened not with the rise of modern science, nor with the appearance of modern historical consciousness, but with his own critique of the equation of the act of being with the existence of beings. In the entire course of philosophical history, according to Heidegger, being itself, the very act of being, was mistaken for, or attributed to, a particular being, most notably the highest being. With Heidegger, this error has been corrected. Even Friedrich Nietzsche, in this view, had to be seen as a metaphysical thinker. True, he was an atheist, but he still believed in a highest being, namely, the will to power. The difficulty”the irony, if you will”in Heidegger’s position is that in the Aristotelian tradition it was precisely being as such , not the highest being, that was the proper subject of metaphysics. In fact, Heidegger excluded philosophical theology but not metaphysics. Nothing could be more metaphysical than Heidegger’s doctrine of being.

Oddly enough, it may well turn out that it is not philosophical theology but the idea of being as such that is obsolete. The idea of being as such would seem to require that general concepts be interpreted as realities rather than as creations of the human mind in the process of ordering the content of experience. In the Aristotelian tradition, the concept of being is simply the most general of general concepts. Since William of Ockham in the fourteenth century and the subsequent rise of modern empiricist philosophy, universal concepts are no longer taken to be realities. As Immanuel Kant argued in his Critique of Pure Reason (1781), the original function of the word being is to be found in our judgments about whether something is or is not . It was in the hypostasizing of being that can be traced from Parmenides through Plato that being was thought of as true or absolute being.

In modern philosophical theology after Descartes and especially after Kant, the concept of being lost the fundamental importance it had in medieval philosophy. The traditional philosophical “demonstrations” of the existence of God as first cause of the universe and therefore as first being were replaced over time by the idea of God as the presupposition of human subjectivity and of its intellectual and ethical functions. The idea of God as first cause of the universe was not abandoned, but it was approached by another line of argument. In Hegel’s rehabilitation of the traditional demonstrations of God’s existence, in response to Kant’s powerful critique, the arguments were recast in terms of the rise of the human mind beyond finite reality to the idea of the infinite.

In this understanding, the idea of the infinite is the prior condition for perceiving the finite. Finite beings are conceived”as Descartes had already argued in Meditations (1641)”by being delimited by the infinite, which therefore is prior to anything finite, including even the human subject itself. Rising beyond the finite to the idea of the infinite belongs to the very nature of the human intellect. This, it was said, is evident historically in the fact of religion and is expressed theoretically in the rational arguments for the existence of God.

Friedrich Schleiermacher’s speeches of 1799 developed this line of argument with respect to the fact of religion. Religion expresses the human sense of the infinite as the prior condition for conceiving anything finite. In Hegel, too, the idea of the infinite replaces the concept of being or of the highest being as that concept functioned in medieval philosophical theology. This new approach to philosophical theology, however, did not abandon the conception of God as first cause of the universe, the creator of everything. What was changed was the way of reaching that conception.

In the late nineteenth and early twentieth centuries, philosophical theology fell on hard times. The intellectual climate turned against the metaphysical and, as noted, Protestant theologians turned to the task of dehellenizing Christian thought. Karl Barth’s great Nein! to natural theology and its replacement by a neo-orthodox theology of revelation alone was of enormous influence. Nor can we underestimate the role of Rudolf Bultmann and his program of demythologizing aimed at purging Christian theology of what he viewed as its philosophical accretions.

Meanwhile, after the battle against modernism initiated by Pius X, Neoscholasticism dominated Roman Catholic theology until the Second Vatican Council. Only a few Catholic theologians, Karl Rahner being notable among them, appropriated the approach of modern philosophical theology in conceiving God from the perspective of human subjectivity. Among Protestants, William Temple in Britain and, most influentially, Paul Tillich, at first in Germany and later in America, developed philosophical theology as a clear alternative to Barth. Employing the modern approach of human subjectivity, Tillich proposed the idea of God as being itself ”not a being, not even the supreme being, but being itself. In this, Tillich’s proposal was similar to that of Heidegger’s.

At the same time, other American thinkers engaged philosophical theology on the basis of Whitehead’s process philosophy. While the school of process theology is still with us, it has never been able to overcome the difficulty that, in Whitehead’s thought, God is only one factor among others in explaining the real world of human experience. It is far from clear how this God can be the biblical creator of heaven and earth. Which, one must add, is not to deny that process philosophy has been helpful in the dialogue between religion and science and in exploring the relationship between faith and reason.

As in the apostolic era and through the centuries, the crucial issue is how to conceive of the one God, creator of all that is. For philosophical theology, different cultural situations require different arguments. Today, for instance, we must address the arguments of modern atheism. Moreover, it is necessary to show how God can be conceived of as the creator of the universe as that universe is described by natural science. This does not necessarily mean that the existence of a creator can be demonstrated by means of natural science, as was thought in medieval and early modern philosophy. Rational argument in philosophy is different from rational argument in science. But a philosophical or theological conception of God as creator must be compatible with the universe as described by science.

We do well to remember that the biblical account of creation employed the natural science of that time, most notably Babylonian cosmology. So also will a contemporary account of creation employ contemporary science, including modern cosmology and theories about the evolution of life. Employing such resources today is in continuity with the methods employed by the writers of the Genesis accounts of creation.

There is yet another factor that is crucially important in this consideration of philosophical theology. Theology that is distinctively Christian will attribute the creation to the trinitarian God”Father, Son, and Holy Spirit. In Christian theology, there is no room for a pre-trinitarian monotheism of the one God. In our time of intense interreligious discussion, Christians cannot compromise the truth that the trinitarian conception of God is not simply a Christian addition to a monotheism that we otherwise share with others. The Christian insistence is that God as such is to be understood as a differentiated unity. An un differentiated unity means unity opposed to the many. Unity that is opposed to the many presupposes and therefore is conditioned by that opposition. Precisely because that is a conditioned unity, it cannot be the absolute unity that is before and above the many. Only the triune God, as differentiated unity, is absolutely and unconditionally the one God. It follows that true monotheism is trinitarian.

In the teaching of Jesus, the name of the one God is Father. This is no mere metaphor but the name of God. As Athanasius insisted, God as Father cannot be conceived apart from a Son. Thus the Son is the eternal correlate of God the Father and is identical with the Logos (Word) of God by which all things were created, both Father and Son being united in eternal communion with the Spirit. This trinitarian understanding of the one God is one of the most important developments of Christian theology in the past century, with both Karl Barth and Karl Rahner playing a leading role in underscoring its importance. It has contributed immeasurably to our understanding of what it means to say that trinitarian faith is monotheistic.

Also important is the deeper appreciation of the roots of this understanding in the Old Testament.

The Hebrew Bible speaks of the one God as Father; and the king, the successor of David, is called his son (Ps. 2:7, 2 Sam. 7:14). The entire people of Israel is also called his son (Hosea 11:1). So the idea of the “son of God” does not occur first with Jesus, although the New Testament understands Jesus to be the definitive manifestation of the eternal Word, the incarnate Son of the Father. Moreover, it is promised that those who believe are incorporated into the Son’s relationship with the Father. The nature of this relationship is manifested in the Son’s obedience to the Father in fulfilling the mission received from the Father, which mission the Father confirmed by raising Jesus from the dead (Rom. 1:4).

This trinitarian understanding of God is crucial to what Christians claim about the unity of faith and reason. Without compromising the transcendence of God, it enables Christians to affirm the presence of the one God in his creation and in the history of his creation. This view allows for, and even requires, a historical interpretation of the biblical texts. They are understood as expressing the mind of the human authors while, at the same time, respecting the Bible’s divine authority as inspired testimony to the action and word of God. The human nature of the biblical writings makes room for the possibility of their including legendary materials, a possibility that is suggested by literary criteria.

At the same time, reported events are not to be declared legendary simply because they are unusual. Reports of the Resurrection of Jesus from the dead, to cite a crucial instance, are not legendary in character. There is absolutely no textual evidence to suggest that they are legendary. If the belief in God as creator and lord of history is not excluded, there is no reason for the exegete not to understand the biblical accounts of the Resurrection to be reporting an actual event in human history. Here again, faith and reason are not in conflict.

The real conflict in our day is over the nature of reason. A secularist concept of rationality that is widely accepted today simply precludes the possibility of a historical event such as the Resurrection of Jesus, just as it precludes the reality of a creator God and his presence and actions in the world of his creation. But this is not, first of all, a disagreement about the truth of such claims. Rather, it is a disagreement about the nature of reason. While there is no conflict in principle between reason and faith, Christian faith is in conflict with a truncated concept of reason that is itself not warranted by reason. Christian intellectuals need to more accurately locate the point of conflict with contemporary deformations of rationality, and more effectively contend for preserving and advancing a history of thought marked by greater confidence in the capacities and imperatives of reason itself.

Wolfhart Pannenberg is professor emeritus of theology of the University of Munich and the author of many books, including Jesus: God and Man and a three-volume systematic theology.