Painted Ladies and the Witch of Endor: Response to John O’Callaghan’s “Can We Demonstrate that God Exists”?

Ralph McInerny, when he gave the Gifford Lectures in Glasgow, considered the difficulties for natural theology of recent developments in philosophy; the fruit of these lectures was his delightfully titled study, Characters in Search of Their Author.¹ Essentially, that study considered attacks on the traditional proofs for the existence of God leveled by non-believers. In preparing those lectures, however, Professor McInerny was confirmed in his belief that a far more disturbing development was the rejection of Aquinas’s proofs by influential Catholic thinkers. He thus wrote his last work of philosophy, Praeambula fidei: Thomism and the God of the Philosophers, which he introduces by stating that he intended to treat “the negative attitude toward natural theology that is found among those one would have expected to be defenders of it.”²

Principal among those whom we would have expected to be defenders of it is Ralph’s dear and brilliant student and successor at the University of Notre Dame, Professor John O’Callaghan. What would Ralph say, if, like the witch of Endor, we had disturbed him from his merited rest, and brought him here to listen to Dr. O’Callaghan’s frightful affirmation that: “the statement God exists is not subject to a deductively valid argument that proceeds from premises that do not employ elements of divine revelation”? Would Ralph furiously revise his work, tearfully to include his wayward intellectual son among his rogues gallery of rejecters? I hesitate to say that he would, especially since Professor McInerny, as a careful listener, would invite us to ask: what exactly is being rejected?

First, let us consider what Professor O’Callaghan is not rejecting. He holds that the philosopher can demonstrate that a god exists (and that this is what Aquinas does in the second question of the first part of the Summa theologiae, in his famous five ways).³ Next, he further holds that the philosopher can demonstrate that there is only one God (and that this is what Aquinas does in question 11 of the Prima pars).⁴ Although some will be surprised to learn that the five ways do not prove that there is only one God, but merely that a god exists, this is entirely in line with the best Thomistic scholarship. As Fr. Larry Dewan has recently written, when we seek to know whether something exists “before asking: ‘is there only one or are there many?’ we must ask: ‘is it a sort-of-thing to be found in reality?’”⁵ Thus, Aquinas’s five ways present “five avenues, five pathways, in humanly experienced reality that conclude to the existence of a god.”⁶

We might ask, therefore, if the philosophers can discover that a god exists and that this god is the only god, where is the problem? The problem arises when we ask whether we are employing the word “God” as a common term or as a proper name. Thus far in the argument, virtually all Thomists would agree that Aquinas employs the word “god” as a common term: as Aquinas himself affirms, it denotes a nature that, at least logically, could be shared by other members of that nature.⁷ (It was thus not logically nonsensical for the patriarch Jacob, in Gen 35:2–3, to tell his family to put away the foreign gods that were among them and go make sacrifice to the God that had saved him, even though later his decedents would learn from the prophets, such as Isa 37:18–20, that the gods of the heathens are not.)⁸ Professor O’Callaghan, therefore, is uncontroversial when he affirms that, when philosophers (including Aquinas in the early questions of the Summa theologiae) speak of a god that they recognize to be the only god, they employ the word “god” as a common term.

The controversy begins when he turns to the believers’ affirmation of faith in God. Specifically, he advances that, when believers affirm that God exists, they are employing the...