In 1654, eight years before his death, the brilliant French mathematician, scientist and philosopher Blaise Pascal had a powerful religious experience that lasted two hours and has come to be known as “the night of fire”. From roughly 10.30pm to 12.30am, Pascal claims to have encountered God. Ever the scientist, Pascal attempted to write down what was happening to him during the experience. What he managed to write down is as follows:

We began this book by considering the evidentialist objection to religious belief. The objection, as you will recall, insists that all beliefs – with religious beliefs as no exception – must enjoy the support of adequate evidence if we are to believe them rationally. Most evidentialists insist that one not only have evidence, but also that one see how and to what degree one's evidence supports the target belief. In the light of this requirement, it is quite plain how the evidentialist's demand is congruent with the natural theologian's practice of forming arguments for God's existence, whose premises and strength of conclusion are evident. In this chapter, we consider two positions that, for differing reasons, do not attempt to meet the evidentialist demand, but reject it. Pascal is famous for thinking that, even if theism cannot be underwritten by so-called proofs for God's existence, belief in God is nevertheless rational on prudential grounds, because of the good ends religious belief brings about. Second, we shall explore a position most famously forwarded by Alvin Plantinga, referred to frequently as “Reformed epistemology”, stemming from the fact that he, and fellow Reformed epistemologists follow John Calvin and Martin Luther's rejection of natural theology. Belief in God, they argue, should be accepted as “properly basic”, without the need for argumentative support.

Pragmatic arguments

Pascal, to whom the reader has already been introduced, was no stranger to the tradition of natural theology.

The debate concerning God's existence, like many debates in philosophy – the success of sceptical arguments, the nature of time, the moral permissibility of war and scores of examples like them – is a matter on which the best philosophical minds disagree. Partisans of both sides can be found who present and defend their arguments with rigour and sophistication, find these arguments compelling and at the same time seem to have a clear understanding of their opponents' views. From this we can, I think, derive several lessons. One obvious lesson is that this debate, like most debates in philosophy (indeed, like many debates in academia) is one for which we should not soon expect some final philosophical resolution. Nor can we insist that all parties who find themselves in such protracted debates simply suspend judgement, for this would require that most academics jettison many of their intellectual commitments. Besides, the very principle that mandates suspension of belief in the face of disagreement is itself a matter of disagreement, thus hoist on its own petard, as they say.

Second, a small dose of intellectual humility and generosity should help us to appreciate that persons of good mind and sincere will can be found on either side of the debate. This, in turn, should preclude quick dismissals of those with whom we disagree as silly, stupid or in open defiance of the most basic standards of rationality. Respect rather than ridicule for one's interlocutors is the only way forward.

The kalam cosmological argument

We have looked at a sampling of arguments, all of which claim that the world's organization, or the functioning of its parts, can best be explained as the handiwork of God. Opponents of such arguments deny that supernatural agency must be invoked; they believe we have perfectly rational and, perhaps, superior explanations that rely solely on natural laws and processes. The cosmological argument for God's existence does not focus on the world's organization, but on its very existence. The question can be put succinctly: why is there something rather than nothing? At first glance, three options present themselves for explaining the world's existence: (i) in one form or another, the material world has always existed; (ii) the material world simply popped into being out of nothing; (iii) the material world had a beginning in time and was brought into being by something immaterial. Theists, of course, opt for the last explanation. We shall explore two versions of the cosmological argument: the kalam cosmological argument, which has its origins in medieval Muslim philosophy, and the argument from contingency. Each claims that theism best accounts for the existence of the cosmos.

Common sense tells us that effects have causes. If there is a fire in the garage, there must be a cause responsible, be it faulty wiring, arson, flammable chemicals or some combination of causes. The principle that all effects have causes applies to the universe as a whole. If the universe began to exist, then it too must have had a cause of its existence.

Why philosophize about God?

If God exists, one is naturally led to ask what sort of being is God. Theists and non-theists alike have a stake in posing the question. Theists, of course, have in interest in knowing the central object of their devotion. Christians, for instance, claim that the highest state of heavenly beatitude consists in “seeing God face to face”, of “knowing as we have been known”. In his Proslogion, Anselm of Canterbury prays to God: “Lord, You give understanding to faith, grant me that I may understand, as much as You see fit, that You exist as we believe You to exist, and that You are what we believe You to be” (1998: 87). Anselm takes metaphysical investigations into God's nature to follow naturally upon one's desire to know better the being one worships. As a lover wishes to know all he can of the beloved, so Anselm wishes to know God, as God is the object of his heart's highest desire. At the very least, authentic devotion to God requires that one endeavour to think truthfully about God.

Some critics of theism urge careful study of the metaphysics of theism as a way of showing that the concept of an omnipotent, omniscient and omnibenevolent being is incoherent and, if incoherent, irrational. We would not bother to investigate the intellectual credentials of the claim that in the remotest parts of Australia there reside animals that are simultaneously insect and mammal since, given what we know about the properties of each, we know this to be a physical impossibility.

Suppose there is a personal being perfect in wisdom, power and goodness, who created the world and sustains it in existence from moment to moment, and that your highest flourishing in this life and the next depends on your being rightly related to this being. In short, suppose that God exists. This, in a nutshell, is what theists profess the world over: a belief that unites the great monotheistic religions of Judaism, Christianity and Islam. If theism is true, it is a matter of incalculable weightiness, which partially explains why theism has been of perennial interest to philosophers. Two questions dominate philosophical writings about God. First, do we have good reasons to think that theism is true? In other words, do we have good reasons to think that anything answers to the description “omnipotent, omniscient, omnibenevolent creator and sustainer of the universe”? Second, if such a being exists, what is he like and how shall we understand his relation to the world? Few questions have so engaged philosophical attention, with new books appearing each year to defend opposing answers to these questions. The first question claims some priority, for if we conclude that no good reasons can be found to think that God exists, it scarcely seems that the second question merits much attention. But the two questions are not so easily separated. For one of the chief reasons cited by some philosophers for thinking that God does not exist is that he cannot exist! Some philosophers argue that the concept of an omnipotent, omniscient, omnibenevolent God is incoherent, so nothing could answer to this description.

The teleological and cosmological arguments arise out of commonplace experiences of a contingent world that displays order. The ontological argument, by contrast, is purely a priori, which is to say, it is not grounded in everyday experience but arises from reflection alone. In a nutshell, it claims that if one truly understands the concept of God and what it is for God to be perfect, one must acknowledge that he exists, for a truly perfect being could not lack existence and still be perfect. As we will see, it is one of the more abstruse arguments in the philosophical repertoire, as it turns on complex reflections about the nature of necessity and the possibility of a necessarily existing being. Ever since it was first penned by Anselm of Canterbury nearly a thousand years ago, it has commanded considerable attention from some of philosophy's leading lights: Berkeley, Locke, Hume, Descartes, Spinoza, Leibniz, Kant, Hegel and Schopenhauer, among others, wrestled with it, some to defend and others to reject it. Even Bertrand Russell, one of the twentieth century's most famous atheists was, for a time, convinced by it.

The analogical design argument

We begin our study of natural theology with design arguments, not because they are logically prior to the other arguments for God's existence, but because they are grounded in so common and widespread an experience – that of beholding the complexity, grandeur and apparent design of the world around us. How many of us have cast a heavenward glance at the star-studded sky on a spectacularly clear night and been moved to the thought “surely this could not have come about by sheer accident, but must be the work of some supernatural being”? Or, for those whose wonder is moved by the microcosmic, how many of us lazily stretched out on a lawn have fixed upon a single blade of grass, contemplated the cellular machinery necessary to produce chlorophyll, and been moved to the same thought? Surely, our initial sentiments suggest that the world and all it contains could not have arisen by accident, that it must be the work of an intelligent agent; and who better than God to produce a world of such scale and intricacy?

Whittaker Chambers, who gave important evidence against convicted Communist spy Alger Hiss during the Cold War, wrote in his book Witness:

We have surveyed a trio of famous arguments for God's existence, the teleological, cosmological and ontological arguments, which their most ardent proponents offer as “proofs” of God's existence. Many theists see these arguments in less exalted terms, perhaps as offering good reasons for thinking that God exists but not as decisive proofs that settle the issue of God's existence once and for all. Even if the arguments thus far surveyed are sound, they suffer other limitations. The teleological and cosmological arguments suffer potentially from the “gap problem”, while the ontological argument suffers from a lack of cogency: no one is likely to accept its most crucial premise who is not already committed to its conclusion. In the next two chapters, we shall explore two other oft-cited bases for rational religious belief: the arguments from morality and religious experience. Each presents us with a pervasive feature of human experience and proceeds to argue that these experiences cannot be adequately explained or understood without acknowledging God's existence. Not unexpectedly, critics will contend that these phenomena can be adequately explained without appealing to supernatural causes or beings.

Moral phenomena

Let us begin our reflections about the rich and complex world of moral experience with a few simple stories. A few years ago, City of Chicago police officers witnessed a drug transaction in an alleyway. One of the men involved in the transaction pulled a gun, whereupon the officers drew their weapons, ordering the man to drop his gun.

John Rawls, author of A Theory of Justice, arguably the most influential treatment of the subject in the twentieth century, grew up a faithful Christian. His Christian convictions were fully on display in his undergraduate thesis at Princeton University, titled “A Brief Inquiry Into the Meaning of Sin and Faith”. His ardent faith foundered, however, by what he experienced as a soldier during the Second World War. Rawls (as so many others) was particularly troubled by the Holocaust. “How could I pray,” wrote Rawls, “and ask God to help me, or my family, or my country, or any other cherished thing I cared about, when God would not save millions of Jews from Hitler?” (Rawls 2009: 263). Rawls is but one of untold numbers of people whose commitment to classical theism has been severely challenged and even abandoned by the obvious incongruity between an all-loving, all-powerful, providential God and the world's pervasive pain and suffering. If an infinitely loving God has all power and knowledge at his disposal, could he not have thwarted the genocidal campaign of the Nazis? Surely it would pose no problem for the almighty to turn back a tidal wave or two, to prevent the AIDS virus from jumping to the human gene pool or, at the very least, to ensure that suffering does not befall innocent children and animals. The chief question we must wrestle with is whether or not the extent and severity of the world's suffering undermines the rational credibility of theism.