Christian philosophy as natural theology
Natural theology is generally characterized as the attempt to establish religious truths by rational argument and without reliance upon alleged revelations. It has focused traditionally on the topics of the existence of God and the immortality of the soul.
Arguments for the existence of God
The design (or teleological) argument
St. Paul, and many others in the Greco-Roman world, believed that the existence of God is evident from the appearances of nature: “Ever since the creation of the world his invisible nature, namely, his eternal power and deity, has been clearly perceived in the things that have been made” (Romans 1:20). The most popular, because the most accessible, of the theistic arguments is that which infers a divine designer from perceived evidence of design in nature. The argument, propounded by medieval Christian thinkers, was developed in great detail in 17th- and 18th-century Europe by writers such as Robert Boyle, John Ray, Samuel Clarke, and William Derham and at the beginning of the 19th century by William Paley. They asked: Is not the eye as manifestly designed for seeing, and the ear for hearing, as a pen for writing or a clock for telling the time; and does not such design imply a designer? The belief that the universe is a coherent and efficiently functioning system likewise, in this view, indicates a divine intelligence behind it.
The argument from design was criticized by the Scottish philosopher David Hume in his Dialogues Concerning Natural Religion (1779). Hume conceded that the world constitutes a more or less smoothly functioning system; indeed, he points out, it could not exist otherwise. He suggests, however, that this may have come about as a result of the chance permutations of particles falling into a temporary or permanent self-sustaining order, which thus has the appearance of design. A century later the idea of order without design was rendered more plausible by Charles Darwin’s discovery that the adaptations of the forms of life are a result of the natural selection of inherited characteristics having positive, and the elimination of those having negative, survival value within a changing environment. Hume also pointed out that, even if one could infer an intelligent designer of the world, one would not thereby be entitled to claim that such a designer is the infinitely good and powerful Creator who is the object of Christian faith. For the world is apparently imperfect, containing many inbuilt occasions of pain and suffering, and one cannot legitimately infer a greater perfection in the cause than is observed in the effect.
In the 20th century, however, the design argument was reformulated in more comprehensive ways, particularly by the British philosophers Frederick R. Tennant (Philosophical Theology, 1928–30) and Richard Swinburne (using Thomas Bayes’s probability theorem in The Existence of God, 1979), taking account not only of the order and functioning of nature but also of the “fit” between human intelligence and the universe, whereby humans can understand its workings, as well as human aesthetic, moral, and religious experience. There were also attempts to show that the evolution of the universe, from the “big bang” of 13.8 billion years ago to the present state that includes conscious life, required the conjunction of so many individually improbable factors as to be inexplicable except as the result of a deliberate coordinating control. If, for example, the initial heat of the expanding universe, or its total mass, or the strength of the force of gravity, or the mass of neutrinos, or the strength of the strong nuclear force, had been different by a small margin, there would have been no galaxies, no stars, no planets, and hence no life. Surely, it was argued, all this must be the work of God creating the conditions for human existence.
These probability arguments were, however, strongly criticized. A basic consideration relevant to them all is that there is by definition only one universe, and it is difficult to see how its existence, either with or without God, can be assessed as having a specific degree of probability in any objective sense. It can of course be said that any form in which the universe might be is statistically enormously improbable, as it is only one of a virtual infinity of possible forms. But its actual form is no more improbable, in this sense, than innumerable others. It is only the fact that humans are part of it that makes it seem so special, requiring a transcendent explanation. Debate about the design argument continued through the late 20th and early 21st centuries, particularly in the United States (see also intelligent design).
The cosmological argument
Aquinas gave the first-cause argument and the argument from contingency—both forms of cosmological reasoning—a central place for many centuries in the Christian enterprise of natural theology. (Similar arguments also appeared in parallel strands of Islamic philosophy.) Thomas’s formulations (Summa theologiae, I, Q. 2, art. 3) were refined in modern neo-Thomist discussions and remained topics of Christian philosophical reflection during the 20th century.
The first-cause argument begins with the assumption that there is change in the world. Change is always the effect of some cause or causes. Each cause is itself the effect of a further cause or set of causes; this chain moves in a series that either never ends or is completed by a first cause, which must be of a radically different nature in that it is not itself caused. Such a first cause is an important aspect, though not the entirety, of what Christianity means by God.
Although taking a different route, the argument from contingency follows the same basic movement of thought from the nature of the world to its ultimate ground. It starts with the premise that everything in the world is contingent for its existence upon other factors. Its presence is thus not self-explanatory but can only be understood by reference beyond itself to prior or wider circumstances that have brought it about. These other circumstances are also contingent, pointing beyond themselves for the ground of their intelligibility. If this explanatory regress is unending, explanation is perpetually postponed and nothing is finally explained. The existence of anything and everything thus remains ultimately unintelligible. But rational beings are committed to the search for intelligibility and cannot rest content until it is found. The universe can only finally be intelligible as the creation of an ontologically necessary being who is eternal and whose existence is not contingent upon anything else. This is also part of what Christianity has meant by God.
Criticism of these arguments points to the possibility that there is no first cause because the universe had no beginning, having existed throughout time, and is itself the necessary being that has existed eternally and without dependence upon anything else. Proponents of the cosmological argument reply that the existence of such a universe, as a procession of contingent events without beginning, would still be ultimately unintelligible. On the other hand, a personal consciousness and will, constituting a self-existent Creator of the universe, would be intrinsically intelligible; for human beings have experience in themselves of intelligence and free will as creative. Critics respond that insofar as the argument is sound it leaves one with the choice between believing that the universe is ultimately intelligible, because created by a self-existent personal will, or accepting that it is finally unintelligible, simply the ultimate given brute fact. The cosmological argument does not, however, compel one to choose the first alternative; logically, the second remains equally possible.
The ontological argument
The ontological argument, which proceeds not from the world to its Creator but from the idea of God to the reality of God, was first clearly formulated by St. Anselm (1033/34–1109) in his Proslogion (1077–78). Anselm began with the concept of God as that than which nothing greater can be conceived (aliquid quo nihil majus cogitari possit). To think of such a being as existing only in thought and not also in reality involves a contradiction. For an X that lacks real existence is not that than which no greater can be conceived. A yet greater being would be X with the further attribute of existence. Thus the unsurpassably perfect being must exist—otherwise it would not be unsurpassably perfect.
This argument has intrigued philosophers ever since. After some discussion in the 13th century it was reformulated by Descartes in his Meditations (1641). Descartes made explicit the assumption, implicit in Anselm’s reasoning, that existence is an attribute that a given X can have or fail to have. It follows from this—together with the assumption that existence is an attribute that is better to have than to lack—that God, as unsurpassably perfect, cannot lack the attribute of existence.
It was the assumption that existence is a predicate that has, in the view of most subsequent philosophers, proved fatal to the argument. The criticism was first made by Descartes’s contemporary Pierre Gassendi and later and more prominently by the German philosopher Immanuel Kant (1724–1804) in his Critique of Pure Reason (1781). Bertrand Russell and others in the 20th century further clarified this objection. According to Russell, to say that something with stated properties—whether it be a triangle, defined as a three-sided plane figure, or God, defined as an unsurpassably perfect being—exists is not to attribute to it a further property, namely existence, but to assert that the concept is instantiated—that there actually are instances of that concept. But whether or not a given concept is instantiated is a question of fact. It cannot be determined a priori but only by whatever is the appropriate method for discovering a fact of that kind. This need for observation cannot be circumvented by writing existence into the definition of the concept (“an existing three-sided plane figure,” “an existing unsurpassably perfect being”), for the need arises again as the question of whether this enlarged concept is instantiated.
In the 20th century several Christian philosophers (notably Charles Hartshorne, Norman Malcolm, and Alvin Plantinga) asserted the validity of a second form of Anselm’s argument. This hinges upon “necessary existence,” a property with even higher value than “existence.” A being that necessarily exists cannot coherently be thought not to exist. And so God, as the unsurpassably perfect being, must have necessary existence—and therefore must exist. This argument, however, has been criticized as failing to observe the distinction between logical and ontological, or factual, necessity. Logically necessary existence, it is said, is an incoherent idea, for logical necessity applies to the relations between concepts, not to their instantiation. God’s necessity, then, must be an ontologically, or factually, rather than a logically, necessary existence: God exists as the ultimate fact, without beginning or end and without depending upon anything else for existence. But whether this concept of an ontologically necessary being is instantiated cannot be determined a priori. It cannot be validly inferred from the idea of an eternal and independent being that there actually is such a being.
Moral arguments
Moral theistic argument belongs primarily to the modern world and perhaps reflects the modern lack of confidence in metaphysical constructions. Kant, having rejected the cosmological, ontological, and design proofs, argued in the Critique of Practical Reason (1788) that the existence of God, though not directly provable, is a necessary postulate of the moral life. To take seriously the awareness of a categorical imperative to act rightly is to commit oneself to work for an ideal state of affairs in which perfect goodness and happiness coincide. But as this universal apportioning of happiness to virtue is beyond human power, a divine agent capable of bringing it about must be assumed.
Other Christian thinkers, particularly during the 19th and early 20th centuries, argued that to accept the absolute demands of ethical obligation is to presuppose a morally structured universe, which implies a personal God whose commands are reflected in the human conscience. It cannot be proved that this is such a universe, but it is inevitably assumed in acknowledging the claims of morality.
Attempts to trace ethical obligation to a transcendent divine source have been criticized on the grounds that it is possible to account for morality without going beyond the human realm. It has been argued that the exigencies of communal life require agreed codes of behaviour, which become internalized in the process of socialization as moral laws; and the natural affection that develops among humans produces the more occasional sense of a call to heroic self-sacrifice on behalf of others.
Arguments from religious experience and miracles
Religious experience is used in Christian apologetics in two ways—in the argument from religious experiences to God as their cause and in the claim that it is (in the absence of contrary indications) as reasonable to trust religious as it is to trust nonreligious experience in forming beliefs about the total environment. (The first use is considered here; for the second, see below Contemporary discussions.)
The argument maintains that special episodes, such as seeing visions of Christ or Mary or hearing the voice of God, as well as the more pervasive experience of “living in God’s presence” or of “absolute dependence upon a higher power,” constitute evidence of God as their source. Although such experiences may be accepted as having occurred, their cause, as critics have noted, might be purely natural. To establish that the experiences are real, as experiences, is not to establish that they are caused by an infinite, omnipotent, omniscient, divine being. As Thomas Hobbes succinctly put it, when someone says that God has spoken to him in a dream, this “is no more than to say he dreamed that God spake to him” (Leviathan, Pt. III, ch. 32).
The analogous argument, from miracles to God as their cause, is more complex and involves two sets of problems. The argument may assert that the children of Israel were miraculously rescued from Egypt or Jesus was miraculously raised from the dead and therefore that God must exist as the agent of these miracles. The first problem concerns the reports. Whereas in the case of private religious experiences the skeptic (to whom the argument is addressed) may well be willing to grant that such experiences occurred, in the case of public miracles the skeptic will require adequate evidence for the described event; and this is not forthcoming for the classic miracle stories referring to alleged extraordinary events of many centuries ago. There are, however, well-evidenced contemporary and recent accounts of “miraculous” healings and other remarkable happenings. On the assumption that some of these, and also some of the classic miracle stories, are historically accurate, the second problem arises. How can it be established that these events were caused by divine intervention rather than by the operation of natural phenomena?
Once again, strict proof seems to be lacking. These arguments, however, display aspects of the explanatory power of the idea of God. Divine activity is not the only possible way of understanding the character of the universe, its contingent existence, the unconditional claims of morality, or the occurrence of religious experiences and “miracles.” Nevertheless, the concept of deity offers a possible, satisfying answer to the fundamental questions to which these various factors point. These questions may thus be said to open the door to rational theistic belief—while still leaving the nonbeliever waiting for a positive impetus to go through that door. The work of some contemporary Christian philosophers can be characterized as a search for such a positive impetus.
The immortality of the soul
Human beings seem always to have had some notion of a shadowy double that survives the death of the body. But the idea of the soul as a mental entity, with intellectual and moral qualities, interacting with a physical organism but capable of continuing after its dissolution, derives in Western thought from Plato and entered into Judaism during approximately the last century before the Common Era and thence into Christianity. In Jewish and Christian thinking it has existed in tension with the idea of the resurrection of the person conceived as an indissoluble psychophysical unity. Christian thought gradually settled into a pattern that required both of these apparently divergent ideas. At death the soul is separated from the body and exists in a conscious or unconscious disembodied state. But on the future Day of Judgment souls will be re-embodied (whether in their former but now transfigured earthly bodies or in new resurrection bodies) and will live eternally in the heavenly kingdom.
Within this framework, philosophical discussion has centred mainly on the idea of the immaterial soul and its capacity to survive the death of the body. Plato, in the Phaedo, argued that the soul is inherently indestructible. To destroy something, including the body, is to disintegrate it into its constituent elements; but the soul, as a mental entity, is not composed of parts and is thus an indissoluble unity. Although Aquinas’s concept of the soul, as the “form” of the body, was derived from Aristotle rather than Plato, Aquinas too argued for its indestructibility (Summa theologiae, I, Q. 76, art. 6). The French philosopher Jacques Maritain (1882–1973), a modern Thomist, summarized the conclusion as follows: “A spiritual soul cannot be corrupted, since it possesses no matter; it cannot be disintegrated, since it has no substantial parts; it cannot lose its individual unity, since it is self-subsisting, nor its internal energy since it contains within itself all the sources of its energies” (The Range of Reason, 1952). But though it is possible to define the soul in such a way that it is incorruptible, indissoluble, and self-subsisting, critics have asked whether there is any good reason to think that souls as thus defined exist. If, on the other hand, the soul means the conscious mind or personality—something whose immortality would be of great interest to human beings—this does not seem to be an indissoluble unity. On the contrary, it seems to have a kind of organic unity that can vary in degree but that is also capable of fragmentation and dissolution.
Much modern philosophical analysis of the concept of mind is inhospitable to the idea of immortality, for it equates mental life with the functioning of the physical brain (see mind, philosophy of). Impressed by evidence of the dependence of mind on brain, some Christian thinkers have been willing to accept the view—corresponding to the ancient Hebrew understanding—of the human being as an indissoluble psychophysical unity, but these thinkers have still maintained a belief in immortality, not as the mind surviving the body, but as a divine resurrection or re-creation of the living body-mind totality. Such resurrection persons would presumably be located in a space different from that which they now inhabit and would presumably undergo a development from the condition of a dying person to that of a viable inhabitant of the resurrection world. But all theories in this area have their own difficulties, and alternative theories emerged.
Kant offered a different kind of argument for immortality—as a postulate of the moral life. The claim of the moral law demands that human beings become perfect. This is something that can never be finally achieved but only asymptotically approached, and such an unending approach requires the unending existence of the soul. This argument also is open to criticism. Are humans indeed subject to a strict obligation to attain moral perfection? Might not their obligation, as finite creatures, be to do the best they can? But this does not seem to entail immortality.
It should be noted that the debate concerning arguments about the immortality of the soul and the existence of God has been as much among Christian philosophers as between them and non-Christian thinkers. It is by no means the case that Christian thinkers have all regarded the project of natural theology as viable. There have indeed been, and are, many who hold that divine existence can be definitively proved or shown to be objectively probable. But many others not only hold that the attempted proofs all require premises that a disbeliever is under no rational obligation to accept but also question the evidentialist assumption that the only route to rational theistic belief is by inference from previously accepted evidence-stating premises.