But it is not possible to know that by looking at the natural world alone. The question of purpose is closely related to the question of whether something like the God of Western monotheistic religions can be known to exist by studying the order, goodness, and grandeur of the universe. Already around 1750 David Hume pointed out that if one is looking at evidence of design, then all of the evidence must be taken into account: not only order and goodness but disorder and evil as well. He seems to think that some sort of creator is possible (in his Dialogues Concerning Natural Religion, published posthumously in 1779, it is not clear which character represents Hume's own views). But if so, we can know next to nothing about the creator's qualities: an intelligence, for all we know, as much like ours as our intelligence is like the rotting of a turnip–one deity or a team; alive or dead; a juvenile or superannuated deity. Nothing can be known of any plan for the future perfection of the world or the human condition.

If one cannot infer the purposes of a benevolent creator from evidence in the natural world, then how can I (and my co-religionists) claim to know the world's purpose? The answer is too complicated to spell out here, but I take it to involve detailed comparisons of competing traditions on the basis of the support they draw from their own peculiar kinds of evidence (for Christians, historical events as in the life of Jesus and the early church, and carefully evaluated religious experiences). In addition, each tradition must be evaluated on the basis of the intellectual crises it faces. Two crises facing what I call the scientific naturalist tradition (originating in Hume's and others' writings) are the questions of whether it is possible adequately to explain the phenomenon of religion naturalistically, and whether the tradition can provide grounds for morality.

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Scientific research on the practices and beliefs of religious adherents is relevant to the first.

Scientific research is also relevant to some of the crises facing theistic traditions, and so knowledge of nature is not irrelevant to the issue of purpose. For example, a long-standing challenge to Christianity is to explain why a good God permits so much suffering of humans and animals at the hand of nature. Why are there tsunamis, hurricanes, droughts, and ghastly diseases? Before the development of modern science (and still in some Christian circles) these were all seen as caused by sin (the Fall) and as fitting punishment for sin.

Now we know that animals suffered for millions of years before humans evolved. We also know that all of these catastrophes are produced by the ordinary working of the processes of nature, such as plate tectonics. Yet one can then ask why God did not create a more benevolent natural order. If it is the strength of gravity that causes broken bones when children fall, why not a kinder, gentler gravitational force?

Here is one point where greater knowledge of the natural world bears on a theological problem. Since the writings of Brandon Carter in 1974 we have had increasingly detailed knowledge of the way in which fundamental constants and physical laws appear to be fine-tuned to produce a universe that supports life. Change any of the numbers slightly, and the development of the entire universe would have gone quite differently, making the evolution of life impossible. For example, the ratio of the strength of gravity to one of the other basic forces, the nuclear weak force, had to be adjusted as accurately as one part in 10 to the 100th power to avoid either a swift collapse of the universe or an explosion.

These scientific developments can be used to argue that, if there is a designer God whose purpose for the universe includes life, especially intelligent life, then the laws and constants had to be almost exactly what they are. Thus, if we are to be here, the natural world must contain almost exactly the amount of danger and destruction that it does.

So while the study of the natural world cannot show that it has a purpose–the fine-tuning is not an adequate argument for the existence of God–it is indeed indirectly relevant to the question of the universe's purpose.