How Can the Existence of God Be Proved?

A CONSIDERABLE AMOUNT of energy has been spent on trying to show that the existence of God is philosophically provable. In reading the medieval philosophers one could reasonably ask why this enterprise was taken up at all, since all the medieval thinkers believed in the existence of a deity. Nevertheless, this was not an idle question for them. Given their deep commitment to philosophy, either as an independent intellectual discipline or as a ‘handmaiden’ of theology, medieval philosophers and theologians attempted to show that, however the relationship of philosophy to religion was to be defined, on the issue of God's existence there would be no disagreement. Here philosophy and religion were in complete harmony. Indeed, if we go back to Aristotle's understanding of the science that ultimately became known as metaphysics, we see that one of his characterizations of this discipline is the study of the divine, and many of the medievals called metaphysics, ‘the divine science’. Moreover, both Plato and Aristotle had a monotheistic conception of the divine. So given this agreement, the medieval preoccupation with this issue is a bit puzzling.

To understand the relevance of this topic to medieval philosophy it will be useful to adopt the terminology of Thomas Aquinas. In attempting to delineate the distinct domain of theology, Aquinas distinguished between the ‘preambles of faith’ and the ‘articles of faith’. Whereas the latter is theology proper, the dogmas of a particular religion, the former is where philosophy and religion intersect. It is here that philosophy and religion have a common language and set of concerns. And it is here that philosophy undertakes to prove some of the fundamental beliefs of religion, such as the existence of God. Equivalent expressions for Aquinas’ ‘preambles of faith’ have been used: ‘natural theology’, ‘philosophical theology’, ‘natural religion’. The underlying assumption here is that human reason is able to prove and explain some of the basic beliefs of monotheistic religion. It is not only the common ground for philosophy and religion, but it is also a place where the monotheistic religions can speak to each other without religiously based assumptions.