Every year, I teach the classic theistic arguments in my philosophy of religion class. We start with the “ontological” argument in Anselm’s Proslogion. Steeped as it is in monastic and biblical prayer, the Proslogion is more like a journey toward the intellectual vision of God than it is like a chapter in a philosophy textbook; yet in a few short paragraphs, Anselm contends rather ingeniously that for God, understood as “something than which nothing greater can be thought,” nonexistence is simply not a conceivable option.

My students find Anselm wonderfully discombobulating. On the one hand, his confession, at the beginning of the Proslogion, of the parlous state of his mind and soul strikes them as pathologically self-deprecating; on the other hand, his claim to have captured “a single argument that needed nothing other than itself” to prove God’s existence seems audacious in the extreme. We moderns are used to occupying a limited middle range between self-trust and self-doubt; our confidence in reason will never soar as high as Anselm’s, while our “skepticism of the instrument” (as H. G. Wells called it) will never sink as low. Compared to Anselm, we are Caspar Milquetoast.

Thomas Aquinas, the next figure on our syllabus, is no less humble and no less daring than Anselm, though he differs with him on the best means of approach. For Thomas, philosophical demonstration of God’s existence, though a mere “preamble” to the fullness of the faith, is a healthy use of our God-given reason and can be done with confidence. Rather than a single argument, Thomas proposes a number of pathways: one may reason from effects to a logically prior first cause, from contingent beings to necessary being, from relative goods to their maximum, from final causation (or teleology) in nature to an intelligence who directs natural bodies to their proper ends, and so on. Follow any of these pathways, Thomas tells us, and though it may lead only to the outer portico of the divine mysteries, it will demonstrate with absolute certainty that God truly and necessarily exists.

Every year, after some weeks spent on Anselm and Thomas Aquinas, I ask my students to devise their own hypothetical argument for God. It’s an exercise they evidently enjoy, for the suggestions spill forth almost faster than I can write them on the board. Here, for example, is a transcript of last year’s blackboard:

Schrödinger’s cat, the failure of attempts to disprove the existence of God, DNA, antientropic processes, love, altruism, miracles, the consensus of the dead—ancestors and traditions, the consensus of the living, basic needs not otherwise met, mystery, pervasive human misery and its solace in prayer, the sense of right and wrong, beauty, multiverses, consciousness, dreams and visions, death

One student proposed what we dubbed the “ichthyological” argument, reasoning to God from the marvelous creatures that dwell near the ocean floor where no one can see them.

Leaving aside the fact that some of these items have been used to bolster arguments against belief in God, what I find striking is the tentative character of our discussion. The atheists as well as the theists in my class seem to have no trouble coming up with an endless variety of reasons and motivations for belief, but absolute certainty is off the table.

Recognizing this difference in reasoning styles actually seems to help students read Anselm and Thomas Aquinas with greater appreciation. One kind of reasoning, evident in the above list, is like a beachcomber who collects from here and there bright shards of experience suggestive of a greater whole. The other kind of reasoning, in principle a priori and universal, is like a well digger who tunnels down to the source and ground of all possible experience.

Thomas Aquinas is a well digger even when he argues from final causes in nature to an intelligent designer. But more recent teleological arguments—those that infer intelligent design from biological complexity or from the fine-tuning of physical constants necessary for a life-permitting universe—are beachcombers. The well digger, if successful, strikes solid certainty. The beachcomber, if successful, can only gather glittering bits of evidence that make the existence of God seem more likely than not; and the beachcomber’s risk is that the glittering bits of evidence may crumble when new facts or more fruitful explanatory models come to light.

The reasoning of the well digger is ordered, complete, and, in its best advocates, embedded in a life of prayer. The reasoning of the beachcomber is suggestive, probabilistic, and unfinished; yet its very tentativeness lends it a poignancy that can draw the inquirer toward prayerful assent. Both kinds of reasoning deserve to be cultivated by believers; each has its time and season. As Chesterton once pointed out, “A man is not really convinced of a philosophic theory when he finds that something proves it. He is only really convinced when he finds that everything proves it.” I’ll take Anselm’s logic of perfection, Thomas’s five ways to find God through effects, and Schrödinger’s cat—and then add to the list of arguments for God the remarkable fact that our minds are capable of such reflections, whether on the beach or at the well.

Carol Zaleski

Carol Zaleski is professor of world religions at Smith College in Northampton, Massachusetts.

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