Arguments for the existence of God

The design (or teleological) argument

St. Paul, with 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 identifies evidences of design in nature, inferring from them a divine designer. The argument was propounded by medieval Christian thinkers and was developed in great detail in 17th- and 18th-century Europe by such writers as Robert Boyle, John Ray, Samuel Clarke, and William Derham and at the beginning of the 19th century by William Paley. Such writers 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 fact that the universe as a whole is a coherent and efficiently functioning system likewise, in this view, indicates a divine intelligence behind it.

This kind of argument was powerfully criticized by the Scottish philosopher David Hume in his Dialogues Concerning Natural Religion (1779). Hume granted 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 animal pain and human 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 has been reformulated in more comprehensive ways, particularly by the British philosophers Frederick R. Tennant (Philosophical Theology, 1928-30) and Richard Swinburne (using 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 one can understand its workings, as well as human aesthetic, moral, and religious experience. There are also attempts to show that the evolution of the universe, from the "big bang" of some 15,000,000,000 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 is argued, all this must be the work of God creating the conditions for human existence.

These probability arguments have, however, been 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. The design argument is thus an area in which debate continues.

The cosmological argument

St. Thomas 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 were also used in parallel strands of Islamic philosophy.) Thomas' formulations (Summa theologiae, I, Q. 2, art. 3) have been refined in modern neo-Thomist discussions and continue to be topics of Christian philosophical reflection.

The first-cause argument begins with the fact that there is change in the world. A 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.

The argument from contingency follows by another route the same basic movement of thought from the nature of the world to its ultimate ground. It starts with the fact 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 likewise contingent; they too point 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 thus 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.