The Ontological Argument for God's Existence.

Is God’s Existence Built Into the Concept of God?

Understanding the Ontological Argument

When it comes to arguments for the existence of God, most people are familiar with ones based on evidence, such as the complexity of the universe or the moral law within. But one of the most fascinating and controversial arguments doesn’t rely on physical evidence at all. It’s called the ontological argument, and it’s based purely on logic and definitions—a type of reasoning philosophers call a priori.

What Is A Priori Reasoning?

A priori reasoning refers to arguments that don’t depend on observation or experience. Instead, they rely on logic, concepts, and definitions alone. For example, we know that “all bachelors are unmarried” not by checking the marital status of every bachelor, but simply by understanding the definition of the word “bachelor.”

The ontological argument uses this same kind of reasoning to argue that God’s existence is logically necessary.

Anselm’s Classic Argument

The ontological argument was first clearly formulated by Anselm of Canterbury in the 11th century. Anselm defined God as “that than which nothing greater can be conceived.” In other words, God is the greatest possible being one can imagine.

Anselm then reasoned that it’s greater for a being to exist in reality than merely in the mind. If God only existed as an idea, then a greater being—one that exists in reality—could be conceived. But that would contradict the definition of God as the greatest conceivable being. Therefore, God must exist in reality, not just in the mind.

It’s a bold argument—almost like saying that the very idea of God proves that God must be real.

Descartes and Plantinga: Building on Anselm

René Descartes, a 17th-century philosopher, offered a similar version. He argued that existence is a necessary part of a perfect being, just like having three sides is a necessary part of a triangle. If we truly understand what a perfect being is, we must also understand that such a being exists.

In modern times, Alvin Plantinga has developed a version of the ontological argument using modal logic (logic involving possibility and necessity). He argues that if it's even possible that a maximally great being exists, then such a being must exist in all possible worlds, including our own.

These versions aim to make Anselm’s logic more precise, but the core idea remains the same: God's existence is not just a possibility—it’s a necessity.

Common Objections

Despite its elegance, the ontological argument has faced serious criticism. The most famous objection comes from Immanuel Kant, who argued that existence is not a predicate—in other words, it’s not a quality that adds something to the concept of a being. You can’t define something into existence, Kant said, just by saying that it must exist.

Others argue that the ontological argument assumes what it’s trying to prove—that God exists in reality—without actual evidence. For many, the leap from definition to existence feels like a logical trick rather than sound proof.

Why It Still Matters

So why is the ontological argument still discussed? Because it’s unique among theistic arguments. It challenges us to think about the nature of existence, the limits of logic, and what we mean by “God.” Even those who find it unconvincing often acknowledge its depth and philosophical richness.

More importantly, it adds to the cumulative case for God’s existence. While it may not persuade everyone on its own, it complements other arguments, like those from cosmology, morality, and design, to form a broader framework for theism.

Final Thoughts

Is the ontological argument compelling? That depends on how much weight you give to logical reasoning over empirical evidence. Some find it profound; others find it unconvincing. Either way, it raises an important question: If we can conceive of the greatest possible being, does that being’s existence necessarily follow?

It’s a question worth pondering, because how we answer it touches not only on philosophy, but on the very foundations of faith.