From Augustine to Anselm: Tracing the Roots of Arguments for God’s Existence

The question of whether God exists has never been purely a matter of faith. For centuries, some of the greatest minds in Western history tried to answer it through reason alone – not by pointing to miracles or scriptures, but by examining what we know about truth, greatness, and the nature of reality itself. Two thinkers who laid the very foundation of this rational tradition were St. Augustine of Hippo (354-430 CE) and St. Anselm of Canterbury (1033-1109 CE). Their arguments, separated by nearly seven centuries, represent two distinct but deeply connected approaches to proving God’s existence – one turning inward to the soul, the other working outward from pure logic. Understanding these arguments means understanding where the philosophy of religion begins.

Augustine’s starting point: the inner world of the soul 🔗

St. Augustine was not a detached academic philosopher. He was a man who had lived through doubt, intellectual wandering, and a restless search for meaning before arriving at Christianity. That personal journey is woven directly into his philosophical method. Rather than looking at the external world for evidence of God, Augustine looked inward – to the human soul, its longing for happiness, and its capacity to grasp eternal truths.

His argument unfolds most systematically in his dialogue De libero arbitrio (On Free Choice of the Will), completed around 395 CE. The core claim is this: some truths exist in a timeless, unchanging state. Mathematical facts like “seven plus three equals ten,” logical necessities, and moral standards hold for everyone, everywhere, at all times. They did not come into being when humans began thinking about them, and they would not disappear if every human mind ceased to exist. Augustine calls these eternal truths.

The argument from eternal truths 🔗

The reasoning moves in clear steps. Eternal truths cannot be the product of human minds, because human minds are finite, changeable, and mortal. For a truth like “seven plus three equals ten” to exist as an eternal reality, it must reside in a mind – but not in any human mind, since human minds are not eternal. There must therefore be an eternal mind in which these truths permanently reside. That eternal mind, Augustine concludes, is God.

In Augustine’s own words from the dialogue, he tells his interlocutor that if something can be shown to be higher than our minds – something unchanging and eternal – then that something is either God, or if anything higher still exists, that higher thing is God. Either way, God exists. Augustine identifies what is superior to our minds and reason as God – the classical formulation of the argument from eternal forms.

This is not merely an abstract logical exercise for Augustine. It connects to a broader metaphysical claim: God is not just one being among others but is Truth itself – the ground in which all true things participate. The eternal truths we recognize are, in a sense, glimpses of the divine mind.

The soul’s desire for happiness 🔗

Augustine pairs this argument with a second, more existential strand. In his Confessions, he describes the human soul as marked by a restless longing that no earthly thing can satisfy. Wealth, pleasure, and knowledge all fall short of truly fulfilling us. Augustine believed this universal desire is not escapism but the soul’s memory of its Creator – a built-in orientation toward God that, when denied, leaves the person perpetually dissatisfied.

This argument has an interesting structure: it does not just claim that God exists, but that the very shape of human longing points toward something real. If we consistently find that nothing finite satisfies us, and if (as Augustine believes) genuine desires correspond to real objects, then there must exist an infinite being that alone can fulfill that desire. The restlessness is, in effect, a kind of proof.

Criticisms of Augustine’s argument 🔗

Augustine’s arguments opened important doors, but they also attracted significant pushback – and he himself acknowledged their limitations. In the dialogue format of De libero arbitrio, he describes his own arguments as “sure yet tenuous,” an honest admission that they do not deliver a knock-down proof.

The most persistent objection to the eternal truths argument is that it may not be necessary to invoke a divine mind at all. Critics point out that eternal truths could simply be abstract entities – like numbers – that exist independently of any mind, in the manner that Plato described with his theory of Forms. If so, you do not need God to explain them; they just are. Augustine was aware of this Platonic alternative, and later thinkers like Edward Feser have worked to close this gap by arguing that abstract objects cannot exist independently of any intellect – but this remains a live philosophical debate.

The argument from the soul’s desire is even more vulnerable to skepticism. Critics argue it relies heavily on subjective experience. Not everyone reports the same sense of inner restlessness, and even those who do might explain it through psychology, biology, or culture rather than theology. The leap from “I feel a longing nothing earthly satisfies” to “therefore an infinite God exists” is not logically airtight. Augustine’s introspective method, while deeply influential, was not designed to produce the kind of universally verifiable proof that later philosophers would demand.

Anselm’s ontological argument: from concept to reality 🔗

Nearly seven centuries after Augustine, St. Anselm, Archbishop of Canterbury, attempted something far more audacious: a single argument for God’s existence that required no empirical premises at all – no observations about the world, no introspective experience of the soul, just the logic embedded in the very concept of God.

Anselm had composed an earlier work, the Monologion, containing several traditional arguments for God’s existence. Unsatisfied, he searched for one self-sufficient argument that could stand alone. After great intellectual effort, he arrived at what became known as the ontological argument, presented in his 1078 work the Proslogion.

The core logic of the Proslogion 🔗

Anselm defines God as “that than which nothing greater can be conceived” – the greatest possible being. He then observes that even a person who denies God’s existence understands this concept. The atheist, when told of a being than which nothing greater can be conceived, grasps what is being said. That concept, at minimum, exists in the understanding.

Now Anselm introduces his critical move. If the greatest possible being exists only in the mind but not in reality, then a greater being can still be conceived – one that exists both in mind and in reality. But that would mean the greatest conceivable being is not actually the greatest conceivable being, which is a contradiction. Therefore, the greatest conceivable being must exist not only in the mind but also in reality. God exists.

Put plainly: existence in reality is greater than existence in the mind alone. If God – by definition the greatest possible being – lacked real existence, God would fall short of being the greatest possible being. The concept of God therefore entails his existence. This is what makes the argument ontological: it moves from the very nature of being, from the definition of what God is, directly to the conclusion that God must be.

The second argument: necessary existence 🔗

Anselm actually presents a second, stronger version of the argument in Chapter 3 of the Proslogion. In this version, a being whose non-existence is logically impossible is greater than one whose non-existence is merely possible. God, as the greatest conceivable being, must therefore exist necessarily – meaning it would be a logical contradiction to say God does not exist, in the same way that it is contradictory to say a square has three sides. This “necessary existence” formulation proved more resilient to criticism than the first and continued to influence philosophers like Descartes, Leibniz, and in the twentieth century, Alvin Plantinga.

Criticisms of Anselm’s argument 🔗

The ontological argument fascinated and frustrated philosophers in equal measure almost from the moment it was written. Critiques began with Gaunilo, a contemporary monk of Anselm, and the debate has not stopped since.

Gaunilo’s perfect island 🔗

Gaunilo, writing in defense of the atheist “fool” whom Anselm addressed, produced the most famous early parody of the argument. He argued that Anselm’s logic could be used to prove the existence of a perfect island: if we can conceive of the greatest possible island, and if it would be greater for it to exist in reality than only in the mind, then the perfect island must exist. But this is clearly absurd – we cannot conjure islands into existence by defining them as great. So something must be wrong with Anselm’s reasoning.

Anselm’s reply was pointed: an island, however perfect, is by nature a limited and contingent thing. You can always conceive of a better island. But God, as the greatest possible being, possesses all perfections to the ultimate degree – the very notion of “something greater” has no application. The island analogy fails because it applies to a finite category; God, by definition, belongs to no such category.

Aquinas’s and Kant’s objections 🔗

Thomas Aquinas rejected the idea that God’s existence can be deduced purely from the concept of God, arguing that different people hold different conceptions of God, and not everyone defines the divine in the same way Anselm does. For the argument to work, one must already share Anselm’s particular understanding of God as the greatest conceivable being – which an atheist or agnostic may not grant.

The most influential philosophical objection came centuries later from Immanuel Kant. Kant argued that ontological arguments fail because they rely on treating “existence” as a real predicate – as a property that adds something to a concept. But existence, Kant insisted, is not a property in the same sense that “red” or “tall” are properties. Saying that God exists does not add any new characteristic to the concept of God; it only asserts that the concept has an instance in the world. If Kant is right, then saying “the greatest conceivable being exists in reality” adds nothing to the concept, and the entire argument collapses.

From Augustine to Anselm: a progression of thought 🔗

Taken together, Augustine and Anselm represent a movement in early medieval theological philosophy from the experiential to the purely rational. Augustine grounds his case in what the human mind discovers about itself – its grasp of eternal truths, its longing for happiness, its inherent orientation toward something beyond the finite. His argument is personal, introspective, and shaped by his own biography of faith and doubt.

Anselm takes a more radical step. He attempts to derive God’s existence from pure reason, without any appeal to experience whatsoever. Unlike cosmological and teleological arguments that depend on at least one empirical premise, the ontological argument is purely conceptual: just as the definition of a bachelor implies the bachelor is unmarried, the definition of God, according to Anselm, implies that God exists.

Yet the two thinkers are not as distant as they might appear. Augustine’s famous program of fides quaerens intellectum – faith seeking understanding – was explicitly adopted and named by Anselm himself. Both men began from a position of faith and used reason not to replace that faith but to illuminate and defend it. Neither claimed to be converting atheists through argument alone; both were writing primarily for those who already believed but wanted to understand their belief more deeply.

Their arguments also share a philosophical core: the conviction that God is not just one more object in the world but the ultimate ground of reality – for Augustine, the ground of truth; for Anselm, the greatest possible being, whose greatness entails existence. These are different angles on the same fundamental idea.

Their lasting influence on philosophy of religion 🔗

Neither argument ended the debate – if anything, they intensified it. The argument from eternal truths was taken up by Leibniz, who developed his own version, and it continues to appear in contemporary philosophy in discussions of mathematical Platonism and the nature of abstract objects. Leibniz’s proof from eternal truths, directly inspired by Augustine, became a recurring theme in early modern philosophy, reappearing in Malebranche and others who saw it as a powerful response to skepticism.

Anselm’s ontological argument has proved even more philosophically generative. Descartes, Leibniz, Gödel, and Plantinga all produced their own versions, each trying to improve on the original while preserving its central insight. Even those who reject the argument entirely – including Kant – helped shape the field by articulating precisely what is wrong with it, which in turn clarified what a successful proof of God’s existence would need to look like.

These two thinkers, then, did not simply offer early attempts at an argument that later philosophers perfected or discarded. They defined the terms of the debate. The ontological argument has brought very few people to theism on its own – but its enduring presence in philosophy of religion for nearly a thousand years speaks to the depth and difficulty of the questions it raises. When we ask today whether God’s existence can be established by reason alone, we are still, in a fundamental way, continuing the conversation that Augustine began in his study in North Africa and Anselm continued in his monastery in Canterbury.

What do you think? Can an argument built entirely from logic – without any appeal to experience or observation – ever be sufficient to prove that something as profound as God exists? And is Augustine’s claim that the soul’s restless longing points toward God a compelling philosophical argument, or does it rely too heavily on a subjective experience that others may not share?

References

1. https://plato.stanford.edu/entries/augustine/
2. https://philosophicaleggs.com/12-god-and-eternal-truth-part-1-2/
3. https://www.catholic365.com/article/3138/evidence-for-the-existence-of-god-from-experience-part-9-truth.html
4. https://tcdecker.com/2022/10/17/the-existence-of-god-argument-from-eternal-truths/
5. https://tomstheology.blog/2025/02/15/saint-augustines-arguments-for-god/
6. https://iep.utm.edu/anselm-ontological-argument/
7. https://credomag.com/article/anselm-of-canterbury-and-the-ontological-argument/
8. https://en.wikipedia.org/wiki/Ontological_argument
9. https://plato.stanford.edu/entries/ontological-arguments/
10. https://philarchive.org/archive/JUMSAO
11. https://www.mdpi.com/2077-1444/16/2/123
12. https://philopedia.org/works/proslogion-or-discourse-on-the-existence-of-god/