Natural theology is the part of theology that does not depend upon revelation. During the Middle Ages, natural theology included arguments for the existence and nature of God, for the immortality of the soul, and for the basic principles of morality insofar as they are founded on nature as created by God.
The first flourishing of natural theology was in ancient Greece. Plato's dialogue, the Phaedo, contains a number of weak arguments for the everlastingness of the soul, and Aristotle's Metaphysics contains arguments for a "Prime Mover," which is also the best of all possible beings. In the Christian tradition, medieval theologians, often appealing to Romans 1:180, developed the viewed that natural theology could establish the existence of God, which it is logically necessary to do before discussing the things that God had revealed. The first Vatican Council, held from 1869 to 1870, defined as a matter of faith that the existence of God could be demonstrated by reason. The best known arguments in this regard are those of medieval philosopher and theologian Thomas Aquinas, whose "Five Ways" for demonstrating God are drawn from Aristotle.
Aristotle's four causes
In Aristotle's (38422 B.C.E.) work, there is no sharp distinction between physics and theology. The Prime Mover is part of a scientific explanation of the universe, which explains why and for what purpose the universe exists. Aristotle describes four basic types of causes, and a complete causal explanation would trace them to an ultimate self-evident origin. There must be an ultimate efficient cause of the universe, something that brings everything else into being without itself being capable of entering into being or of passing away (it will be eternal). It will cause changes without being capable of change (it will be immutable). It will generate all transient things without itself being affected by anything (it will be necessary). According to Aristotle, there must be an ultimate formal cause of the universeomething that includes the natures of all things in a higher and underived manner (it will contain all possible perfections). There must be an ultimate final cause of the universeomething to which all things strive, or for the sake of which they exist (a perfection that all things strive to imitate in their own way). And there must be an ultimate material cause of the universeomething out of which it is made, which is not itself made out of anything more basic.
For Aristotle, the eternal, immutable, necessary, perfect pattern of the universe is one and the same being, since an all-perfect being will be eternal, immutable, and necessary. Prime matter, however, the material cause, is in itself imperfect and formless, and is a basic brute fact alongside the perfect being. Aquinas (c. 1225274) adopted all these arguments, and agreed with Aristotle that the efficient, formal, and final cause of the universe is not its material cause. But he argued that matter is not an ultimate principle. It is brought into being "ex nihilo" by the cause of the universe which is wholly immaterial and which, he said, "all men call God" (Summa Contra Gentiles 1, 13).
These arguments for God are essentially arguments to an ultimate cause, which will provide an ultimate explanation for the universe. Perhaps the "first cause" simply exists, as the ultimate brute fact. But one might push the argument as far as it can go, and say that the first cause has to exist. It cannot fail to exist, since it is the very source of all possibilities, and without it nothing would be even possible. The twentieth-century philosopher Richard Swinburne calls this an "absolute explanation," since it arrives at a being that is self-explanatory, whereas an ultimate explanation simply arrives at a being that cannot be explained in simpler or more basic terms.
These arguments continue to be the basis for most arguments in natural theology, construed as an attempt to explain the universe, but they have ceased to be considered a part of science. This is largely because science has rejected Aristotelian forms of explanation as being both superfluous and vacuous. Aristotelian science looked for the "essences" or true natures of things, and assumed that the essences must be brought about by things which were like them and at least as "great" in reality, and that each thing must have a "final cause" or purpose for the sake of which it exists.
Since the sixteenth century, scientists have ceased to look for "real essences" or for "final causes," and have given up the causal principle that things must be brought into being by other things that are like but greater than themselves. Such investigations led to no practical results. Instead, the "new scientific method" consisted of close observation, repeated experiment, and the formulation of general precise laws that govern events. Using this new method, one discovers no real essences, final causes, or efficient causes in the sense of beings that "bring about" their effects by some inner propensity. What one finds are sets of general laws and regular principles that are effective in describing and predicting series of events.
"Explanation" becomes the formulation of such laws, and an ultimate explanation would consist in the formulation of a general law that cannot be subsumed under a higher, more general, or simpler law. The idea of a First Cause, in the sense of a perfect and causally efficacious being, has disappeared from science. Science still asks why the ultimate laws of nature exist, but a scientific answer is likely to lie in a demonstration that such laws exist by some sort of inherent necessity. The eternal and perfect originator of the universe of Aquinas has been transformed by science into the inherent necessity of an ultimate mathematical formula, which is not "what all men call God."
Experimental sciences and idealism
Natural theology thus lost its scientific credibility with the rise of the properly experimental sciences. For some, however, this merely indicated that the natural sciences had limited the range of their enquiries to phenomena that could be measured, repeatedly observed, and explained under general mathematical laws. Questions about the ultimate nature, origin, and destiny of the universe remain, and if science does not attempt to answer such questions, then metaphysics or "first philosophy" must try.
As a result, a second stage in the history of natural theology began in seventeenth-century Europe with the rise of philosophical Idealismhe view that the ultimate nature of the universe is spiritual, that physical phenomena are appearances of that spiritual realm, and that the intellect can uncover the structure of the spiritual world, with which the physical sciences cannot deal. It is characteristic of this approach that it seeks to take conscious experience as its fundamental clue to the nature of reality, and to explain physical phenomena as confused appearances of basically conscious entities, or perhaps of one supreme Spirit.
The Idealist approach raises in an acute way the question of the relationship between the sciences and the humanities, or between physical and mental states. It may be claimed that law-like explanation which is open to any detached observer is only appropriate to physical phenomena, whereas one must understand the phenomena of consciousness in terms of interpretation, empathetic understanding, and personal engagement. Whether such a broad difference between human and natural sciences exists and is irreducible, is strongly disputed.
Rationalist or Idealist philosophers seldom agree with one another, and there seems to be no way of objectively verifying their claims. However, this is to be expected from systems that claim to be based on personal engagement and interpretation. The difference between traditional natural theology and Idealist natural theology is clearly exemplified in the writings of German philosopher Immanuel Kant (1724804). Kant is best known for his destructive criticism of the traditional arguments for God, but he firmly believed that there is an underlying reality that is the cause of physical reality as it appears to our senses. According to Kant there can be no theoretical knowledge of such reality in-itself (what he termed "noumenal" reality), but the mind does provide a priori knowledge of the form and order of sensory appearances (so knowledge does not depend merely on empirical information). Knowledge depends on the inner structure of reason, and reason necessarily postulates God, freedom, and immortality as ideas in terms of which we must represent ultimate reality to ourselves.
Kant is also, as are most idealists, firmly committed to science understood as the investigation of the rational structure of phenomenal experience. The claim would be that idealism.e., the postulate that the universe must be thought of as basically mind-likes the surest foundation of the natural sciences, which must presume there is a rational structure in the natural world. But Idealism also points out that there are limits to science, which are reached when it claims to disclose the ultimate structure of reality, or to extend its reach into the realm of the personal or spiritual. That is a realm into which philosophy can reach, with the aid of its principles of rational coherence, establishing a system within which consciousness, value, and purpose can have an intelligible place. The crucial question is whether the concepts of value and purpose have a place in explanations of the universe. If they do, then an Idealist approach offers a complement to science, which only comes into conflict with it if and insofar as value and purpose are denied.
Modern appropriations of the design argument
The failure to establish useful general laws in psychology and sociology, as well as the subjective nature of much of history and economics, suggests that these areas are not amenable to the scientific techniques that have been so useful in physics and chemistry. But the fields of neurophysiology and of evolutionary psychology contain promises (or threats) to explain consciousness itself in physical or evolutionary terms. Consciousness may be a byproduct of past successful survival strategies, and its present functioning may be incidental to the adaptive functions (of discerning prey or avoiding predators) that it originally possessed. This sort of natural theology, which argues from consciousness to a supreme consciousness or Spirit, needs to argue that consciousness is an irreducible and distinctive phenomenon beyond the reach of experimental science. That remains a highly disputed issue.
A third, slightly different approach to natural theology reverts to the methodology of the sciences, not the Aristotelian method of searching for essential natures, but the experimental method of inferring hypotheses from observed evidence. The most famous example of this approach is found in the work of eighteenth-century English theologian William Paley, who inferred from evidences of design in nature the existence of a wise designer. This approach is unlike the Aristotelian approach, since it does not assume that all substances have final causes. Rather, Paley's approach looks at organisms, in particular, as highly organized and efficient systems for supporting animal and human life, and argues that it is much more probable that such systems are designed than that they originated by chance. If we found a watch, says Paley, we would surely infer that it had a designer, it is so intricately organized to a purpose, with all its parts finely balanced and tuned to one another. So we must infer that the world has a designer, for similar reasons.
This approach was dealt a severe blow by Charles Darwin's (1809882) theory of evolution and natural selection, which claims to show how well-designed organisms can evolve, if not by chance, than at least by random mutation and natural adaptation to the environment, in strongly competitive situations. Given the difficulty Paley has in accounting for why such strange organisms as giraffes and ichneuman flies (which lay their eggs in living caterpillars) exist, mutation and natural selection seem a better explanation than trying to figure out why God would design such odd or unpleasant creatures.
Nevertheless, design proponents argue that a wise creator may not have specifically designed every type of creature that exists. But such a creator might have designed the general laws of genetic mutation and environmental selection so that they would generate sentient rational organisms by a process that is partly random, yet directed to certain goals (the existence of rational agency). When one adds to this the extreme improbability of the laws of nature giving rise to a universe with life-forms in it at all, one has an argument to the general elegant design of the laws of nature and of evolution, if not to all their particular products. Many of the findings of physics, which disclose the elegance and integrated simplicity of the fundamental forces of the physical world, and those of biology, which reveal the amazingly complex structure of DNA and the adaptedness of living creatures to their environment, are strongly suggestive of design.
On the other hand, some argue that any universe with conscious beings in it would have to be complex and ordered in just such a way, so it is hardly surprising that we find such complex order. The structure is highly improbable, but so is the existence of any universe at all, so this universe is no more improbable than any other. In addition, it may be doubted whether it makes sense to speak of purpose or direction in evolution, and whether existence is worthwhile at all. So these probabilistic arguments of design-type natural theology are far from conclusive.
It seems that the universe, as science shows it to be, could be the work of an intelligent creator. But the universe may also just happen to exist as it does. The inference to a creator is not strictly required. The arguments of natural theology may seem to make a creator probable to many people. They do show the intelligibility and elegance of the universe, and thus enrich the idea of a creator that a theist might hold. But they are not overwhelming, and non-scientific factors concerning the value and possible purpose of creation will probably weigh the balance one way or another.
Partly for this reason, many theologians deny that religious belief depends upon the success of natural theology. Some, like Swiss theologian Karl Barth (1886996), even argue that the program of natural theology is based on human arrogance, and flies in the face of revelation, which is to be accepted on faith, not because it seems on balance to be probable. Kant said, "I have had to deny knowledge, in order to make room for faith" (p. 29). He meant that only when it could be shown that no speculative knowledge of transcendent reality is possible, so that one could neither affirm nor deny God by argument, was one free to adopt faith on practical or moral grounds.
It has come to be widely held in modern theology that faith results either from a commitment of the will (Søren Kierkegaard ), or from some basic and nonrational apprehension of the holy (Friedrich Schleiermacher  and Rudolf Otto ), or, as according to John Barth, simply from an act of divine grace, which has no rational grounds. The problem with such views is that they prevent anyone from giving a reason why they should adopt one faith (say the Christian) rather than another (Islam, perhaps). Such views are also in danger of isolating religious belief from scientific belief, so that religion and science have no relation to one another. Yet it seems odd to say that religious belief in a creator God is not affected by new discoveries about the nature of the created universe, or that religious beliefs (such as the belief that God is one rational purposive creator) have nothing to say about the nature of such a creation.
Natural theology is often no longer seen as the task of proving that God exists, or of showing to any independent observer that God is the most probable explanation of why the universe is the way it is. But, it might be said, one should be able to assemble the best human knowledge in all the diverse areas of human activity, and show how it can reasonably be construed, and even shaped into a more coherent form, by the insights of religion, which may themselves derive from some distinctive source in revelation or experience. Natural theology will then be the attempt to show how science, history, morality, and the arts are so related that a total integrating vision of the place of humanity in the universe may be formulated. Such a vision will be religious insofar as it includes reference to an encompassing reality that is transcendent in power and value, and that may disclose itself in distinctive ways. This will not be proof, or even probability, starting from some neutral, completely shared ground. It will be an integrating activity of reason, both provisional in its formulations and constructed from a standpoint of specific basic postulates and personal value commitments. Within such a perspective, science will be able to make a positive contribution to natural theology, and natural theology will develop ways of integrating scientific activity into a wider worldview. This will be more of an imaginative art than an inferential or deductive science. It will not be the intellectual foundation or prelude for faith, but will involve the construction of a general worldview within which faith can have an intelligible place. That is not too far from the aims of Aristotle, though the distinctions between natural science, philosophy, and religious belief are now clearer (but only in some ways) than they were for him. In this form, natural theology becomes the speculative and constructive part of the post-eighteenth-century discipline of the "philosophy of religion." As such, it is not confined to one particular religious tradition, and its exponents may hold any or no religious beliefs.
However, there are many philosophers of religion who would hold that systematic construction is not properly part of philosophy, the function of which should be primarily analytic and expository. Therefore, natural theology in all its form remains, like religion itself, a highly pluralistic and disputed discipline. It is clear, however, that this is an area in which science and religion fruitfully interact in examining the fundamental problem of the ultimate nature of existence.
See also ARISTOTLE; DARWIN, CHARLES; DESIGN ARGUMENT; EVOLUTIONARY PSYCHOLOGY; IDEALISM; KANT, IMMANUEL; ; THOMAS AQUINAS
Barrow, John D., and Tipler, Frank J. The Anthropic Cosmological Principle. New York: Oxford University Press, 1986.
Barth, Karl. The Epistle to the Romans (1921), trans. Edwyn Hoskyns. New York: Oxford University Press, 1933.
Davies, Paul. The Mind of God; The Scientific Basis for a Rational World. New York: Simon and Schuster, 1992.
Dennett, Daniel C. Darwin's Dangerous Idea; Evolution and the Meanings of Life. New York: Touchstone, 1995.
Hume, David. Dialogues Concerning Natural Religion (1779). Indianapolis, Ind.: Hackett, 1980.
Kant, Immanuel. Critique of Pure Reason (1781), trans. Norman Kemp Smith. London: Macmillan, 1933.
Kierkegaard, Soren. Concluding Unscientific Postscript to the Philosophical Fragments (1846), trans. Howard V. Hong and Edna H. Hong. Princeton, N.J.: Princeton University Press, 1992.
Otto, Rudolf. The Idea of the Holy (1917), trans. John W. Harvey. London: Oxford University Press, 1923.
Paley, William. Natural Theology (1802), eds. Henry Brougham and Charles Bell. London: C. Knight, 1836.
Schleiermacher, Friedrich. On Religion: Speeches to its Cultured Despisers (1799), trans. Richard Crouter. Cambridge, UK: Cambridge University Press, 1988.
Swinburne, Richard. The Existence of God. New York: Oxford University Press, 1979.
Ward, Keith. God, Chance, and Necessity. Oxford: Oneworld Press, 1996.
Ward, Keith. Religion and Revelation. Oxford: Clarendon Press, 1996.
Wilson, Edward O. Consilience: The Unity of Knowledge. New York: Knopf, 1998.
Did this raise a question for you?