Can God's Existence Be Proven, or Is It Faith Alone?
The sceptic says belief in God is faith without evidence. Many believers quietly agree. The Church has said, solemnly, that both are wrong.
The Objection
Faith is what people fall back on when they have no evidence. If God’s existence could be proven, there would be no need to believe it, and no serious disagreement about it. The fact that intelligent people disagree, and that religion asks for faith at all, shows that belief in God is a matter of trust or upbringing, not of reason. Believers should simply admit it.
What makes this objection interesting is that a good many Christians accept its premise. “You can’t argue anyone into God” is often said from the pulpit as well as from the sceptic’s chair. The Catholic position disagrees with both.
What the Church Actually Claims
The First Vatican Council, in its constitution Dei Filius (1870), taught that God, the beginning and end of all things, can be known with certainty from created things by the natural light of human reason. It drew the teaching from St Paul: “Ever since the creation of the world his invisible nature, namely, his eternal power and deity, has been clearly perceived in the things that have been made” (Romans 1:20). The Book of Wisdom makes the same charge against those who saw the works of creation and failed to recognise the craftsman (Wisdom 13:1–9).
Notice what is and is not being said. The claim is not that everyone in fact knows God exists, or that every argument offered for it is sound. It is that the human mind is capable of reaching that truth from the world it already knows, without first being told by revelation. The capacity belongs to reason as such; whether a given person exercises it well is another matter.
This is the ground on which Aquinas built the Five Ways (Summa Theologiae I, q. 2, a. 3). They are demonstrations of a particular kind: not from a definition of God down to his existence, but from effects in the world — change, causation, contingency, gradation, order — back to a cause they require. Aquinas thought the existence of God was not self-evident to us, which is exactly why it needs demonstrating (I, q. 2, a. 1).
Preambles and Articles
The tradition distinguishes two kinds of truth about God. The preambles of faith — that God exists, that he is one, that he is intelligent — can be reached by reason. The articles of faith — that God is a Trinity, that the Son became man, that he rose from the dead — cannot; they are known only because God has revealed them.
Faith, on this account, is not a substitute for evidence. It is assent to what God has revealed, on the authority of God who reveals. And it presupposes the preambles the way, in Aquinas’s phrase, grace presupposes nature and perfection presupposes something to be perfected (I, q. 2, a. 2, ad 1). You cannot sensibly trust the word of someone whose existence you regard as unknowable.
Then Why Reveal It?
If reason can reach God’s existence, why does Scripture bother to teach it? Aquinas answers this directly at the very start of the Summa (I, q. 1, a. 1). The truths about God that reason can discover would, without revelation, be known only by a few, after a long time, and mixed with many errors. Most people lack the leisure, the training or the temperament for metaphysics; and even good philosophers have reached God by way of serious mistakes about him.
So God revealed even what reason could in principle reach, so that it could be held by everyone, readily, and without error. The Catechism repeats the point (CCC 37–38). Revelation of the preambles is not evidence that reason fails; it is mercy towards the conditions under which reason has to work.
That God exists is demonstrable by reason; what God is in his inner life is known only by revelation. Faith does not fill a gap where evidence should be. It receives, on God’s word, truths reason could never reach — and, for most people, it also holds firmly the truths reason could reach but which few will ever work out for themselves.
Common Replies
”If it can be proven, why don’t all philosophers agree?”
Because a demonstration’s being sound and its being persuasive are different things. The arguments depend on metaphysical premises — about causation, change, and contingency — that take work to grasp and that a whole intellectual culture may have stopped taking seriously. Disagreement shows that the arguments are difficult and contested, which Aquinas expected. It does not show they fail. Many truths in mathematics and philosophy were disputed for centuries before they were settled.
”Doesn’t proof make faith pointless?”
Not for the articles of faith, which no proof can reach. For the preambles, Aquinas allows that one person may know by demonstration what another, who cannot follow the demonstration, holds by faith (I, q. 2, a. 2, ad 1). A believer who has never read a page of metaphysics is not believing irrationally; he is relying on a trustworthy witness, as we all do for most of what we know.
”Scripture says we must believe that God exists” (Hebrews 11:6).
It does, and for most people that belief will rest on revelation rather than argument. Nothing in that contradicts Romans 1:20. The one passage speaks of how we come to God in practice; the other of what the human mind is able to know in principle. The Church holds both.
”What about modern cosmology?”
The Five Ways do not depend on any particular model of the universe’s origin. That is a separate objection, taken up in Does Modern Cosmology Make the First Cause Argument Obsolete?