Arguments for the Existence of God
Throughout the history of philosophy and theology, there have been various arguments for the existence of God. Philosophers and saints of the medieval period, 400–1400 c.e., were notable for producing arguments for God's existence.
St. Aurelius Augustine espoused the dictum Credo ut intellegium — “I believe that I might understand.” As a philosopher and a man of faith, Augustine had to pursue the truth and observe Christian wisdom. To Augustine's mind, faith was primary. Of Augustine's thoughts about the conflict between faith and reason, Aquinas wrote “… Whatever he found contrary to faith, he amended.”
St. Augustine (354–430) offered one of the first arguments for the existence of God. In his book on the will, De Liberio Arbitrio, (The Freedom of the Will), Augustine spelled out the argument. It was manifest to Augustine that our minds are capable of knowing eternal truths. If you think of your mind as a container wherein various eternal and necessary truths are stored, these truths are like effects that require a cause. There must be a causal explanation for this, and Augustine's explanation is that God is the immutable and eternal ground of such truths. The “proof” of God's existence, then, is that the mind is able to think about eternal truths and there must be a cause for these thoughts.
Of course, this “proof” of God's existence reveals Augustine's Platonic heritage. For Plato had argued that if the mind apprehends eternal truths such as perfect justice, beauty, and equality, there must be a world of ideas — of “forms” — that causes the ideas of them.