History of the interactions of philosophy and theology
Influence of Greek philosophy
As the Christian movement expanded beyond its original Jewish nucleus into the Greco-Roman world, it had to understand, explain, and defend itself in terms that were intelligible in an intellectual milieu largely structured by Greek philosophical thought. By the 2nd century ad several competing streams of Greek and Roman philosophy—Middle Platonism, Neoplatonism, Epicureanism, Stoicism—had merged into a common worldview that was basically Neoplatonic, though enriched by the ethical outlook of the Stoics. This constituted the broad intellectual background for most educated people throughout the Roman Empire, functioning in a way comparable to the pervasive contemporary Western secular view of the universe as an autonomous system within which everything can in principle be understood scientifically.
Neoplatonic themes that provided intellectual material for Christian and non-Christian thinkers alike in the early centuries of the Common Era included a hierarchical conception of the universe, with the spiritual on a higher level than the physical; the eternal reality of such values as goodness, truth, and beauty and of the various universals that give specific form to matter; and the tendency of everything to return to its origin in the divine reality. The Christian Apologists, Christian writers of the 2nd century who provided a defense of the faith against prevailing Greco-Roman culture, were at home in this thought-world, and many of them used its ideas and assumptions both in propagating the Gospel and in defending it as a coherent and intellectually tenable system of belief. They accepted the prevailing Neoplatonic worldview and presented Christianity as its fulfillment, correcting and completing rather than replacing it. Philosophy, they thought, was to the Greeks what the Law was to the Jews—a preparation for the Gospel; and several Apologists agreed with the Jewish writer Philo that Greek philosophy must have received much of its wisdom from Moses. Tertullian (c. 155/160–after 220)—who once asked, “What has Athens to do with Jerusalem?”—and Tatian (c. 120–173), on the other hand, rejected pagan learning and philosophy as inimical to the Gospel; and the question has been intermittently discussed by theologians ever since whether the Gospel completes and fulfills the findings of human reason or whether reason is itself so distorted by sin as to be incapable of leading toward the truth.
Greek philosophy, then, provided the organizing principles by which the central Christian doctrines were formulated. It is possible to distinguish between, on the one hand, first-order religious expressions, directly reflecting primary religious experience, and, on the other, the interpretations of these in philosophically formulated doctrines whose articulation both contributes to and is reciprocally conditioned by a comprehensive belief-system. Thus the primitive Christian confession of faith, “Jesus is Lord,” expressed the Disciples’ perception of Jesus as the one through whom God was transformingly present to them and to whom their lives were accordingly oriented in complete trust and commitment. The interpretive process whereby the original experience developed a comprehensive doctrinal superstructure began with the application to Jesus of the two distinctively Jewish concepts of the expected messiah and the Son of man who was to come on the last day and also of the son of God metaphor, which was commonly applied in the ancient world to individuals, whether kings or holy men, who were believed to be close to God. It continued on a more philosophical level with the use, in The Gospel According to John, of the idea of the Logos, drawn both from the Hebraic notions of the Wisdom and the Word of God and from the Greek notion of the Logos as the universal principle of rationality and self-expression. As Jesus, son of God, became Christ, God the Son, the second Person of the Trinity, he was identified with the Logos.
Emergence of official doctrine
During the first several generations of Christian history there was great variety and experimentation in Christian thinking. But as the faith was legally recognized under Constantine in 313 and then became the sole official religion of the Roman Empire under Theodosius, its doctrines had to be formalized throughout the church. This pressure for uniformity provoked intense debates. The orthodox versions of the doctrine of Christ and the Trinity were finally established at the great ecumenical councils (principally Nicaea in 325; Constantinople in 381; and Chalcedon in 451). The key ideas of these Christological and Trinitarian debates and their conclusions were based upon the Greek concepts of ousia (nature or essence) and hypostasis (entity, used as virtually equivalent to prosōpon, person). (In Latin these terms became substantia and persona.) Christ was said to have two natures, one of which was of the same nature (homoousios) as the Father, whereas the other was of the same nature as humanity; and the Trinity was said to consist of one ousia in three hypostases. The Platonic origin of this conceptuality is clear in the explanation of the Cappadocian Fathers that the Father, Son, and Holy Spirit share the same divine ousia in the way Peter, James, and John shared the same humanity.
The influence of Neoplatonism on Christian thought also appears in the response of the greatest of the early Christian thinkers, St. Augustine (354–430), to the perennially challenging question of how it is that evil exists in a world created by an all-good and all-powerful God. Augustine’s answer (which, as refined by later thinkers, remained the standard Christian answer until modern times) includes both theological aspects (the ideas of the fall of angels and then of humans, of the redemption of some by the cross of Christ, and of the ultimate disposal of souls in eternities of bliss and torment) and philosophical aspects. The basic philosophical theme, drawn directly from Neoplatonism, is one that the American philosopher Arthur Lovejoy, in The Great Chain of Being (1936), called the principle of plenitude. This is the idea that the best possible universe does not consist only of the highest kind of creature, the archangels, but contains a maximum richness of variety of modes of being, thus realizing every possible kind of existence from the highest to the lowest. The result is a hierarchy of degrees both of being and of goodness, for the identity of being and goodness was another fundamental idea Augustine inherited from Neoplatonism and in particular from Plotinus (205–270). God, as absolute being and goodness, stands at the summit, with the great chain of being descending through the many forms of spiritual, animal, and plant life down to lifeless matter. Each embodies being and is therefore good on its own level; and together they constitute a universe whose rich variety is beautiful in the sight of God. Evil occurs only when creatures at any level forfeit the distinctive goodness with which the Creator had endowed them. Evil is thus negative or privative, a lack of proper good rather than anything having substance in its own right. This, too, was a theme that had been taken over from Neoplatonism by a number of earlier Christian writers. And if evil is not an entity, or substance, it follows that it was not a part of God’s original creation. It consists instead in the going wrong of something that is in itself good, though also mutable. Augustine locates the origin of this going-wrong in the sinful misuse of freedom by some of the angels and then by the first humans. His theodicy is thus a blend of Neoplatonic and biblical themes and shows clearly the immense influence of Neoplatonism upon Christian thought during its early formative period.
Augustine and Christian thinkers in general departed from Neoplatonism at one crucial point. Neoplatonism maintained that the world was continuous in being with the ultimate divine reality, the One. The One, in its limitless plenitude of being, overflows into the surrounding void, and the descending and attenuating degrees of being constitute the many-leveled universe. In contrast to this emanationist conception Augustine held that the universe is a created realm, brought into existence by God out of nothing (ex nihilo). It has no independent power of being, or aseity, but is contingent, absolutely dependent upon the creative divine power. Further, Augustine emphasized that God did not create the universe out of preexistent matter or chaos, but that “out of nothing” simply means “not out of anything” (De natura boni). This understanding of creation, entailing the universe’s total emptiness of independent self-existence and yet its ultimate goodness as the free expression of God’s creative love, is perhaps the most distinctively Christian contribution to metaphysical thought. It goes beyond the earlier Hebraic understanding in making explicit the ex nihilo character of creation in contrast to the emanationism of the Neoplatonic thought-world. This basic Christian idea entails the value of creaturely life and of the material world itself, its dependence upon God, and the meaningfulness of the whole temporal process as fulfilling an ultimate divine purpose.
Modern Christian treatments of the idea of creation ex nihilo have detached it from a literal use of the Genesis creation myth. The idea of the total dependence of the universe upon God does not preclude the development of the universe in its present phase from the “big bang” onward, including the evolution of the forms of life on Earth. Although creation ex nihilo (a term apparently first introduced into Christian discourse by Irenaeus in the 2nd century) remains the general Christian conception of the relation between God and the physical universe, some 20th-century Christian thinkers substituted the view (derived from Alfred North Whitehead and developed by Charles Hartshorne) that God, instead of being its transcendent Creator, is an aspect of the universe itself, being either the inherent creativity in virtue of which it is a living process or a deity of finite power who seeks to lure the world into ever more valuable forms.
Aristotle and Aquinas
Although Neoplatonism was the major philosophical influence on Christian thought in its early period and has never ceased to be an important element within it, Aristotelianism also shaped Christian teachings. At first known for his works on logic, Aristotle gained fuller appreciation in the 12th and 13th centuries when his works on physics, metaphysics, and ethics became available in Latin, translated either from the Greek or from Arabic sources. Aristotle’s thought had a profound impact on generations of medieval scholars and was crucial for the greatest of the medieval Christian thinkers, St. Thomas Aquinas (c. 1225–74). One of Aristotle’s ideas that particularly influenced Thomas was that knowledge is not innate but is gained from the reports of the senses and from logical inference from self-evident truths. (Thomas, however, in distinction from Aristotle, added divinely revealed propositions to self-evident truths in forming his basis for inference.) Thomas also adopted Aristotle’s conception of metaphysics as the science of being. His doctrine of analogy, according to which statements about God are true analogically rather than univocally, was likewise inspired by Aristotle, as were his distinctions between act and potency, essence and existence, substance and accidents, and the active and passive intellect and his view of the soul as the “form” of the body.
Thomas Aquinas’s system, however, was by no means simply Aristotle Christianized. He did not hesitate to differ from “the Philosopher,” as he called him, when the Christian tradition required this; for whereas Aristotle had been concerned to understand how the world functions, Thomas was also concerned, more fundamentally, to explain why it exists.
With the gradual breakdown of the medieval worldview, the nature of the philosophical enterprise began to change. The French thinker René Descartes (1596–1650) is generally regarded as the father of modern philosophy, and in the new movements of thought that began with him philosophy became less a matter of building and defending comprehensive metaphysical systems, or imagined pictures of the universe, and more a critical probing of presuppositions, categories of thought, and modes of reasoning, as well as an inquiry into what it is to know, how knowledge and belief are arrived at in different areas of life, how well various kinds of beliefs are grounded, and how thought is related to language.
There has long ceased to be a generally accepted philosophical framework, comparable with Neoplatonism, in terms of which Christianity can appropriately be expressed and defended. There is instead a plurality of philosophical perspectives and methods—analytic, phenomenological, idealist, pragmatist, and existentialist. Thus modern Christianity, having inherited a body of doctrines developed in the framework of ancient worldviews that are now virtually defunct, lacks any philosophy of comparable status in terms of which to rethink its beliefs.
In this situation some theologians turned to existentialism, which is not so much a philosophical system as a hard-to-define point of view and style of thinking. Indeed, the earlier existentialists, such as the Danish philosopher Søren Kierkegaard (1813–55), vehemently rejected the idea of a metaphysical system—in particular, for 19th-century existentialists, the Hegelian system—though some later ones, such as the German philosopher Martin Heidegger (1889–1976), developed their own systems. Existentialists are identified by the appearance in their writings of one or more of a number of loosely related themes. These include the significance of the concrete individual in contrast to abstractions and general principles; a stress upon human freedom and choice and the centrality of decision, and hence a view of religion as ultimate commitment; a preference for paradox rather than rational explanation; and the highlighting of certain special modes of experience that cut across ordinary consciousness, particularly a generalized anxiety or dread and the haunting awareness of mortality. Existentialists have been both atheists (e.g., Friedrich Nietzsche and Jean-Paul Sartre) and Christians (e.g., Kierkegaard, the Protestant Rudolf Bultmann, and the Roman Catholic Gabriel Marcel). It would be difficult to identify any doctrines that are common to all these thinkers. Existentialist themes have also been incorporated into systematic Christian theologies (e.g., by John Macquarrie).
Other influences
Others have sought to construct theologies in the mold of 19th-century German idealism (e.g., Paul Tillich); some, as process theologians, in that of the early 20th-century British mathematician and metaphysician Alfred North Whitehead (e.g., Charles Hartshorne on the doctrine of God, John Cobb on Christology); some, the liberation theologians, in highly pragmatic and political terms (e.g., Juan Luis Segundo, Gustavo Gutiérrez); and some, as feminist theologians, in terms of the self-consciousness of women and the awareness of a distorting patriarchal influence on all past forms of Christian thought (e.g., Rosemary Ruether, Elizabeth Fiorenza). Most theologians, however, have continued to accept the traditional structure of Christian beliefs. The more liberal among them have sought to detach these from the older traditions and reformulate them so as to connect with modern consciousness (e.g., Friedrich Schleiermacher, Albrecht Ritschl, Adolf von Harnack, Karl Rahner, Gordon Kaufman); while the more conservative have sought to defend the traditional formulations within an increasingly alien intellectual environment (e.g., B.B. Warfield, Charles Hodge, Karl Barth, Cornelis Berkouwer).
Of the factors forming the intellectual environment of Christian thought in the modern period, perhaps the most powerful have been the physical and human sciences. The former have compelled the rethinking of certain Christian doctrines, as astronomy undermined the assumption of the centrality of the Earth in the universe, as geologic evidence concerning its age rendered implausible the biblical chronology, and as biology located humanity within the larger evolution of the forms of life on Earth. The human sciences of anthropology, psychology, sociology, and history have suggested possible naturalistic explanations of religion itself based, for example, upon the projection of desire for a cosmic father figure, the need for socially cohesive symbols, or the power of royal and priestly classes. Such naturalistic interpretations of religion, together with the ever-widening scientific understanding of the physical universe, have prompted some Christian philosophers to think of the religious ambiguity of the universe as a totality that can, from the human standpoint within it, be interpreted in both naturalistic and religious ways, thus providing scope for the exercise of faith as a free response to the mystery of existence.