Contrary to atheistic boilerplate, Christianity is anything but a crutch for the weak minded and timid hearted. Christians have gone to great lengths over the centuries to show that, while reason is no substitute for faith, and while it can never occupy anything other than a subordinate position with respect to the latter, reason can indeed establish at least the probability of God’s existence. Some Christians have gone further than this to argue that God’s existence is rationally demonstrable – that is, that it can be established with certainty by reason alone.

St. Anselm, the eleventh century bishop of Canterbury, is famous for his “ontological proof” for God. Anselm tried to show that there was no way that God can’t exist. The idea of God, Anselm reasoned, is the idea of a being “than which none greater can be conceived.” When the atheist and the theist deny and affirm God’s existence respectively, it is this idea that they have in mind. But since it is better for a being to have existence than for it to lack it, and since God is, by definition, the best, the conclusion is inescapable: God necessarily exists. It is no more possible, logically, to affirm the idea of God while simultaneously denying His real existence than it is possible to affirm the definition of a “bachelor” while denying that a bachelor is an unmarried man.

The ontological proof has had its share of detractors, many of the earliest and most distinguished of which have been Anselm’s fellow Christians. St. Thomas Aquinas, for example, among the greatest thinkers the world over and himself a proponent of arguments for God’s existence, rejected it on the grounds that it illicitly moved from “the order of ideas” to “the order of things.” Simply put, the idea of God is one thing; God Himself is something else altogether. “God exists” is not self-evidently true to us, and so while the denial of this proposition is false, it is not self-contradictory. Thus, Anselm is mistaken: just because one can conceive God, doesn’t mean that one speaks nonsense in simultaneously denying that God exists.

Aquinas sought to prove God’s existence the only way he thought it was possible to do so – by appealing to experience, not of God, but of the world. From what is seen, Aquinas supposed, we can infer that which can’t be seen. His famous “five ways” argument reasons from five fundamental features of our world – change or motion, causality, contingency, excellence or value, and harmony or order – to the existence of God. That is, only by way of appeal to God, Aquinas contends, can we explain these phenomena.

The one theme that connects the five ways is that of contingency. To put it another way, the five ways argument is, essentially, an argument from contingency. To say that something is contingent is simply to say that it depends upon something else. You and I are contingent, as is this computer on which I type, the chair on which I sit, and everything else of which our world consists. Aquinas’s position is that the phenomena that constitute our world point beyond themselves to a first cause or reason that is not itself contingent, a being that is necessary. A necessary being is a being that contains the reason for its existence “within itself,” so speak, a being the very nature of which is to exist. And this being, Aquinas declares, is what we call God.

Interestingly, although Aquinas and other Christians who advanced arguments from contingency accepted the Genesis creation account, they acknowledged the possibility that the world could have existed forever, as Plato, Aristotle, and the pagans believed. As Father Frederick Copleston, a twentieth century Roman Catholic priest and historian of philosophy, once memorably quipped, whether you have one piece of chocolate or 1,000 pieces of chocolate, chocolate is never going to yield anything other than chocolate. Similarly, whether we are dealing with one contingent thing in the universe or the totality of contingent beings that comprise the universe, that which is contingent is by definition contingent upon something that, ultimately, can’t depend upon anything else.

There are several other arguments for God’s existence that we simply haven’t the time to consider at present. Whether any of them succeed is debatable and, at any rate, beside the point. That Christians labored tirelessly to establish God’s existence upon rational grounds is a fact of which far too many of our contemporaries, Christian and otherwise, need to be reminded, if not taught. Yet there is something else to be gotten from this little history lesson.

What is remarkable is that in presenting them to their Christian brethren, the proponents of these arguments were under no illusions that they were “preaching to the choir.” If they were under any such illusions, they couldn’t sustain them for long. Not that anyone would know it from studying philosophy in any of our secular universities, but medieval Christians anticipated by hundreds of years the considerations against the arguments for God’s existence that David Hume – widely held up in philosophy textbooks as their critic par excellence – wouldn’t raise until the eighteenth century.

William of Ockam, for instance, like Hume much later, rejected the notion that there is a necessary connection between causes and effects: just because A occurs doesn’t mean that B must necessarily occur. Unlike Hume, however, it was Ockam’s interest in safeguarding God’s sovereignty that informed his conclusion that causality is best understood in terms, not of necessity, but of regularity. Creation consists of distinct things that happen to be arranged in the order in which God arranged them. But God could have arranged them otherwise. Thus, there is no necessary connection between them.

There is another reason, though, why Ockam and such medieval thinkers as Nicholas of Autrecourt and John of Mirecourt rejected necessary causality. It is precisely because each thing – each “substance” – that God creates is unique in being fundamentally irreducible to every other that the existence of one can never be inferred from the existence of the other. Yet what this means is that causal arguments for God’s existence of the sort that Aquinas and many others put forward can never be as strong as they had been thought to be.

Contemporary Christians are the inheritors of a rich intellectual tradition. In these weeks leading up to Easter Sunday, they would be well served to explore it.

Jack Kerwick, Ph.D. blogs at www.jackkerwick.com. You can contact him at [email protected]