In lieu of an abstract, here is a brief excerpt of the content:

  • Can We Demonstrate That “God Exists”?
  • John O’Callaghan

“Stans autem Paulus in medio Areopagi, ait: Viri Athenienses, per omnia quasi superstitiosiores vos video. Præteriens enim, et videns simulacra vestra, inveni et aram in qua scriptum erat: Ignoto Deo. Quod ergo ignorantes colitis, hoc ego annuntio vobis”1 (“Then Paul stood up at the Areopagus and said: ‘You Athenians, I see that in every respect you are very religious. For as I walked around looking carefully at your shrines, I even discovered an altar inscribed, “To an Unknown God.” What therefore you unknowingly worship, I proclaim to you’”2) (Acts 17:22–23).

Can we demonstrate that God exists? I want to begin this essay by asking you to consider three statements:

  1. 1). A god exists.

  2. 2). There is only one god.

  3. 3). God exists.

My thesis is that while 1) and 2) are, for the sake of argument, philosophically demonstrable, 3) is not. First, let me say what I mean by philosophically demonstrable. By demonstration, I have in mind at least what Thomas Aquinas argues in the second question of the first part of the Summa Theologiae, which involves the ideal of Aristotelian demonstration as set out in the Posterior Analytics and as commented upon by Aquinas. At the very least, that ideal involves an ideal of [End Page 619] deductive validity. But demonstration adds, among other things, that the premises are true.

By philosophical, again, I mean what Aquinas has in mind in the first question of the first part of the Summa when he argues that it is necessary that there be a discipline in addition to the philosophical disciplines. In making that point, he characterizes the philosophical disciplines as those that proceed by the natural light of human reason without the assistance of divine grace and revelation. And of course, by revelation I have in mind here with Aquinas the revelation made by God to the Jews and fulfilled in Jesus Christ as manifested to the Apostles. So, a demonstration is philosophical for the purposes of this discussion if it does not appeal to revealed truths with the premises it employs.

Thus, my thesis is that the statement God exists is not subject to a deductively valid argument that proceeds from true premises that do not employ elements of divine revelation. Perhaps, at this point, it looks to some as though I am denying a central position that Aquinas holds in the very context of the Summa to which I am appealing for the sense of “philosophically demonstrable”—namely, that “Unde deum esse, secundum quod non est per se notum quoad nos, demonstrabile est per effectus nobis notos.”3 Aquinas clearly uses “demonstrabile” here in characterizing “deum esse.” Others, perhaps who take seriously the councils of the Church, will remind me of the pronouncement of the First Vatican Council that “Si quis dixerit, Deum unum et verum, Creatorem et Dominum nostrum, per ea, quae facta sunt, naturali rationis humanae lumine certo cognosci non posse: anathema sit,”4 where the more recent Catechism of the Catholic Church has “Etenim exsistentia Dei Creatoris potest lumine rationis humanae per eius opera certo cognosci, quamquam haec cognitio saepe obscurata et deformata est errore.”5 [End Page 620]

However, I do not have time here to defend my claim in the face of either Vatican I or the recent Catechism. I will only make my case in relation to Aquinas. But let me be clear. I am not claiming that it cannot be known that God exists. I think it can be known. I just do not think it can be philosophically demonstrated. And I think Aquinas agrees with me. If correct, this point is very important for this gathering to discuss “What Has Athens to Do with Jerusalem? Dialogue between Philosophy and Theology in the 21st Century,” for it suggests that, while the theologian can know that God exists, the philosopher cannot. So what do they have to say to one another about God?

Aquinas on Faith and the Name “God”

To begin arguing my case, I want to point to a curious passage in Aquinas that should give pause to anyone who takes Aquinas’s thought...

pdf

Share