Philosophy
The Ontological Argument for God's Existence
Quick fact
The argument was first formulated by Anselm of Canterbury in 1078 and has fascinated philosophers ever since, including Descartes, Spinoza, and even modern logicians like Kurt Gödel.
Why this is interesting
Can you prove that something exists just by thinking about it? The ontological argument claims that for one particular being—God—the very idea of Him is enough to guarantee His reality.
Read the full explanation
Understanding The Ontological Argument for God's Existence
Imagine a perfect island. Is it the greatest conceivable island? You might add more beaches, nicer weather, or tastier fruit. But even if you think of the perfect island, you could imagine an even better one that actually exists. Existence, it seems, makes things better. Now, apply this to God. By definition, God is the greatest conceivable being—a being than which no greater can be imagined. If such a being existed only in your mind, you could imagine an even greater being—one that also exists in reality. That would be greater. So, to be the greatest conceivable, God must exist in reality, not just in the mind. This is the core of Anselm's ontological argument: if you understand 'God' as the greatest conceivable being, then His existence logically follows.
A deeper explanation
The argument is a deductive, a priori proof: it claims to establish God's existence from the definition of 'God' alone, without needing sensory experience. Anselm's version is a reductio ad absurdum. He imagines the fool who says in his heart, 'There is no God.' Anselm says the fool understands the phrase 'that than which nothing greater can be conceived.' If the fool understands it, then this being exists in the mind. But if it exists only in the mind, then a greater being can be conceived—one that exists also in reality. Thus, the fool would be conceiving of something greater than 'that than which nothing greater can be conceived,' a contradiction. Therefore, the greatest conceivable being must exist. Descartes later proposed a version comparing God's existence to a triangle's angles: just as the essence of a triangle includes having three angles summing to 180 degrees, the essence of a supremely perfect being includes existence. Kant's famous objection was that 'existence is not a predicate'—it doesn't add a new property to a concept, so a nonexistent God isn't 'lesser' than an existent God; existence simply isn't a quality that can be included in a definition. Despite this, the argument persists because it touches on deep questions about logical necessity, the nature of concepts, and whether existence can be a predicate. Modern modal versions, such as Alvin Plantinga's, use possible-world semantics to argue that if it's possible that a maximally great being exists, then it exists necessarily. Thus, the ontological argument remains a powerful tool for exploring the limits of reason and the concept of necessary existence.