Anselm's Ontological Argument and Gaunilo's Objection

Introduction

Welcome to your sixth lesson in our study of Medieval Western Philosophy. In our last session, we navigated Boethius's intricate solution to the conflict between divine foreknowledge and human free will. The key, you'll recall, was his argument that God's nature is eternal, perceiving all of time in a single, simultaneous present. This made God's knowledge a form of "seeing," not "foreseeing," thereby preserving the contingency of our free choices.

Today, we shift from a philosopher defending the coherence of belief to one attempting to prove its object: God himself. We will examine one of the most famous, debated, and intellectually arresting arguments in the entire history of philosophy, proposed by Anselm of Canterbury (1033-1109). Anselm's argument is unique because it is purely a priori—it attempts to prove God's existence not from evidence in the world, but from the very definition of God, using reason alone.

Your learning outcome for this lesson is to reconstruct Anselm's ontological argument from the 'Proslogion' and analyze Gaunilo's objection. We will first unpack Anselm's line of reasoning, then turn to the brilliant parody formulated by his contemporary, Gaunilo, and finally, consider Anselm's defense.

1. Anselm's Argument: From Concept to Reality

Anselm, a Benedictine monk and later the Archbishop of Canterbury, presents his argument in a work called the Proslogion (Discourse). His goal was to find a single, simple argument that could prove God's existence and attributes. The result is what later philosophers, notably Immanuel Kant, would call the "ontological argument," derived from the Greek ontos, meaning 'being' or 'what is'.

The argument begins not with God, but with a specific definition: "a being than which nothing greater can be conceived." Anselm claims that even an atheist (whom he calls "the fool," referencing Psalm 14:1) can understand this concept. The argument then proceeds as a reductio ad absurdum, showing that denying the existence of this being leads to a logical contradiction.

Let's look at a clear, step-by-step reconstruction of the argument.

To summarize the logic you've just read:

1. We can conceive of a "being than which nothing greater can be conceived." This being now exists at least in our understanding.
2. It is greater to exist in reality than to exist only in the understanding.
3. Therefore, if this "greatest conceivable being" existed only in our understanding, we could conceive of an even greater being: one just like it, but which also exists in reality.
4. This creates a contradiction: we would be able to conceive of a being greater than the being than which nothing greater can be conceived.
5. Since the premise (that this being exists only in the understanding) leads to a contradiction, it must be false.
6. Therefore, a being than which nothing greater can be conceived must exist, not only in the understanding, but in reality.

This is a subtle and powerful argument. It claims that for this one specific concept, its very definition logically entails its existence. But does it work?

2. Gaunilo's Objection: The Parody of the Lost Island

Anselm's argument drew an immediate and clever response from another monk, Gaunilo of Marmoutiers. In his text, titled On Behalf of the Fool, Gaunilo argues that Anselm's reasoning is flawed because its logical form could be used to prove the existence of all sorts of imaginary perfect things.

His strategy is not to find a flaw in a specific premise but to create a parody argument that uses the exact same structure to reach an obviously absurd conclusion. If the logical form is the same, but the conclusion is absurd, then the form itself must be invalid.

Gaunilo's point is sharp: if Anselm's proof works for God, it should also work for the "island than which no greater can be conceived." Since we know that this reasoning doesn't magically make a perfect island exist, there must be something wrong with the reasoning itself.

To appreciate the rigor of Gaunilo's critique, it's helpful to see the two arguments laid out in a parallel structure.

3. Anselm's Reply: God as a Special Case

Anselm did not ignore Gaunilo. He wrote a reply asserting that his argument was sound and that Gaunilo's parody failed because it misapplied the logic. Anselm's core defense is that the concept of "that than which nothing greater can be conceived" is unique and cannot be swapped out for islands, unicorns, or anything else.

The key difference, for Anselm, lies in the distinction between contingent being and necessary being.

• An island is a contingent thing. Its existence depends on other things, and we can easily conceive of it not existing. Furthermore, the idea of a "perfect" island is arguably incoherent—couldn't you always make it greater by adding one more beautiful tree or one more pristine beach? There is no intrinsic maximum for "island-ness."
• God, as the greatest conceivable being, must be a necessary being. A being that exists but could fail to exist is less great than a being that cannot fail to exist. Therefore, the very concept of "that than which nothing greater can be conceived" includes the idea of necessary existence. An island's existence is not part of its essence; God's existence, Anselm argues, is.

This move to necessary existence is the heart of Anselm's rebuttal. Gaunilo's parody fails because an island, by its very nature, can only ever have contingent existence.

The debate ultimately hinges on whether "existence" can be treated as a perfection or property that a being can possess, and whether the concept of God is uniquely coherent in a way that other "perfect" things are not. This question would be taken up centuries later by Kant, who famously argued that existence is not a predicate at all.

Conclusion

In this lesson, you have reconstructed and analyzed one of the most intellectually provocative arguments in philosophy. We have seen how Anselm of Canterbury attempted to build an unshakeable bridge from a concept in the mind to a being in reality, using pure logic.

Key Takeaways:

• Anselm's Ontological Argument: An a priori argument that attempts to prove God's existence from his definition as "a being than which nothing greater can be conceived." It works as a reductio ad absurdum, arguing that to deny this being's existence in reality leads to a logical contradiction.
• Gaunilo's Objection: A parody argument (the "Lost Island") that applies Anselm's logic to a contingent object to produce an absurd result, thereby challenging the validity of the logical form itself.
• Anselm's Reply: Anselm defends his argument by claiming it applies uniquely to God. The concept of a "greatest conceivable being" necessarily includes necessary existence, a property that a contingent object like an island cannot have.

This argument represents a high point of scholastic rationalism. In our next lesson, we will turn to a thinker who took a dramatically different approach. We will examine St. Thomas Aquinas's Five Ways, which reject a priori proofs and instead argue for God's existence a posteriori—from evidence and observation of the natural world.