Similarities

1. Conceptual Definition of God: Both Anselm and Descartes start with a definition of God as a being whose essence includes existence. Anselm uses the concept of the greatest conceivable being, and Descartes refers to God as a supremely perfect being.
2. Existence as Necessary: In both arguments, God’s existence is treated as a necessary property of God’s nature. For Anselm, God cannot be conceived as not existing; for Descartes, God must exist because existence is a perfection.
3. A Priori Reasoning: Both arguments are a priori, meaning they rely on reasoning and concepts rather than empirical observation. They argue for God’s existence based purely on the concept of God.

Differences

1. Focus of the Argument: Anselm’s argument emphasizes conceivability—it’s about the idea that God cannot be conceived not to exist if He is the greatest conceivable being. Descartes’ argument, on the other hand, focuses on perfection and existence as one of those perfections.
2. Philosophical Context: Anselm’s argument is deeply theological and presented as a meditation within the context of faith. Descartes’ argument comes from his broader project of establishing certain knowledge, and it is placed within a systematic doubt framework where God’s existence guarantees the certainty of clear and distinct perceptions.
3. Reliance on Other Claims: Anselm’s argument largely stands alone, whereas Descartes’ argument fits within his larger epistemological project, where proving God’s existence is crucial to validate the certainty of human knowledge.

Objections

Several objections apply differently to each argument:

1. Gaunilo’s Island (Applies to Anselm): Gaunilo, a contemporary of Anselm, famously argued that Anselm’s reasoning could be applied to anything. He suggested that one could conceive of a “perfect island” that must exist if Anselm’s logic were sound. This objection points to the potential flaw in Anselm’s reasoning: existence cannot be a property of something merely because it is the greatest conceivable version of that thing. This specific objection is harder to apply to Descartes because his argument does not rest on conceivability in the same way.
2. Kant’s Objection (Applies to Both, but More Strongly to Descartes): Kant famously argued that existence is not a predicate, meaning it is not a property that something can possess. Rather, existence is the condition for having properties in the first place. Kant’s critique is more pointed against Descartes because Descartes frames existence as a perfection, as if it were a property like any other (e.g., wisdom, power). Anselm’s argument, while also vulnerable, might be less directly undermined by this objection since it’s more about the nature of conceptualization than about existence as a property.
3. Existential Import (Applies More to Descartes): Another objection is that Descartes assumes that existence is a necessary part of the definition of perfection, which may be questioned. Why should existence be considered a perfection? This objection doesn’t quite hit Anselm in the same way, because his argument is about logical coherence in the concept of God rather than treating existence as an improvement on a set of perfections.

Conclusion

Both Anselm and Descartes offer arguments that hinge on the nature of God’s existence as tied to His definition. They are similar in their conceptual approach but differ in their underlying frameworks and the nuances of their arguments. The major objections—like Gaunilo’s island and Kant’s critique of existence as a predicate—apply differently to each, reflecting the subtle differences in how each philosopher presents the case for God’s necessary existence.

Prompt: Explain in more detail why Gaunilo’s objection does not apply to Descartes’ argument?

Gaunilo’s objection, known as Gaunilo’s island or the perfect island objection, was formulated in response to Anselm’s ontological argument, and it challenges the idea that one can define something into existence by reasoning that its existence is a necessary part of its perfection or greatness. The objection can be summarized as follows:

1. Anselm’s Argument: Anselm claims that if we can conceive of the greatest conceivable being (God), then this being must exist in reality because a being that exists in reality is greater than one that exists only in the mind.
2. Gaunilo’s Rebuttal: Gaunilo argues that using the same reasoning, one could imagine the greatest conceivable island—a perfect island that has all the best attributes of an island. According to Anselm’s logic, this perfect island must exist in reality because it would be greater if it existed in reality than if it existed only in the mind. However, this is clearly absurd, as simply imagining a perfect island does not mean that such an island actually exists.

This objection is a reductio ad absurdum, showing that Anselm’s reasoning could lead to illogical conclusions if applied to other concepts. However, Gaunilo’s objection is less effective against Descartes’ version of the ontological argument for several reasons:

1. Concept of Perfection

Gaunilo’s objection relies on the fact that imagining a “perfect island” does not make it exist. But Descartes’ argument is not based on any conceivable object like an island, which is a contingent, finite, and imperfect thing. Descartes’ concept of perfection is tied to the specific nature of God, a necessary being whose perfection inherently includes existence. The idea of a perfect island, by contrast, is not grounded in necessity—there is nothing about the concept of an island that requires it to exist.

• Descartes’ God vs. Gaunilo’s Island: Descartes argues that God’s existence is inseparable from His essence. In other words, a being that is supremely perfect necessarily has existence as one of its perfections. By contrast, the concept of a perfect island does not entail necessary existence because islands are contingent objects; they could exist or not exist without affecting the concept of what an island is. Descartes would argue that the concept of God is unique because it involves necessary existence, whereas the concept of an island does not.

2. Contingent vs. Necessary Beings

Gaunilo’s objection applies well to contingent beings like islands because their existence is not required by their definition. A perfect island might be conceivable, but its non-existence does not contradict our understanding of what an island is.

In contrast, Descartes claims that God is a necessary being. For Descartes, the very definition of God as a supremely perfect being includes existence, because not existing would be an imperfection. Since God’s existence is necessary by definition, it cannot be compared to contingent, finite objects like islands, which can exist or not exist without any contradiction.

• Necessity of God: Descartes’ argument is based on the idea that God’s existence is not just possible but logically necessary. You cannot conceive of God as a supremely perfect being without also conceiving of Him as existing. The island, on the other hand, does not have this feature of necessity—there is no contradiction in imagining a perfect island that does not exist. For this reason, the island analogy doesn’t undermine Descartes’ argument because it deals with a completely different type of entity (contingent vs. necessary).

3. Different Focus of the Arguments

Anselm’s argument is primarily based on conceivability—if you can conceive of the greatest possible being, then this being must exist. Gaunilo exploits this by showing that we can conceive of many things that do not exist, like a perfect island.

Descartes’ argument, however, is not so much about conceivability as it is about the nature of perfections. Descartes asserts that existence is a perfection that a supremely perfect being must possess. Therefore, Descartes’ version of the ontological argument centers around the qualities of God, not just the ability to conceive of God.

• Conceivability vs. Perfections: Gaunilo’s critique undermines the assumption that conceivability guarantees existence, but Descartes does not rely on this assumption. He’s making a more technical claim: that a being with all perfections must necessarily exist, because non-existence would be an imperfection. Thus, the idea of a “perfect island” does not challenge Descartes’ logic, since islands are not defined in terms of perfections in the same way that God is.

4. The Specificity of God’s Nature

Descartes’ argument is built upon the unique nature of God as an infinite, supremely perfect being. Unlike an island, which is a specific, finite object that can have varying degrees of perfection (e.g., the best beach, the best weather), the concept of God involves infinite perfections.

• Finite vs. Infinite: A “perfect island” can always be improved in some way (another palm tree, better weather, etc.), but God, by Descartes’ definition, is already maximally perfect in every conceivable way. This intrinsic difference means that Gaunilo’s analogy of the island cannot properly capture the concept of a necessary, infinite being like God. The qualities that make a perfect island are contingent and arbitrary, whereas the perfections that define God (such as omnipotence, omniscience, and necessary existence) are absolute and essential to the concept of God.

Conclusion: Why Gaunilo’s Objection Doesn’t Apply to Descartes

Gaunilo’s objection effectively challenges Anselm’s argument because it shows that you cannot simply define something into existence by imagining it as the greatest possible version of that thing. However, Descartes’ argument avoids this problem by focusing on necessary existence as a feature unique to the concept of a supremely perfect being like God. Gaunilo’s island example relies on contingent concepts that do not share this essential nature, making the objection less applicable to Descartes’ ontological argument.