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A Rational Look at Christianity; Basing Reason in Truth

St. Anselm’s Ontological Argument and Gaunilo’s Perfect Island

Most people have heard of the ontological argument, but few actually know its formulation. The purpose of this short essay is to briefly examine this argument as first enunciated by St. Anselm in his Proslogion. If you have never read the Proslogion, it is worth the time. The Proslogion is only a couple of pages long, yet the discussion that has followed it has filled libraries. This follows from the fact that Anselm’s argument, which to all appearances is logically sound, seems to lead to the conclusion that because one can imagine a perfect something then that perfect something must exist.

Anselm’s arguments begins with the proposition that everyone can envision a being “greater than which cannot be thought of,” i.e., a being who is the greatest thing such that nothing else can be greater. For theists, this is an easy concept because theists in the Judeo-Christian realm regularly deal with the idea of an omnipotent, omniscient and omnipresent God. But Anselm argues that even a skeptic who holds no belief in God or a god can understand and envision the concept of a being “greater than which cannot be thought of.” Once he envisions it, the concept is in his mind, and so even the skeptic must admit that a being “greater than which cannot be thought of” exists in thought if not in reality.

This opening part of Anselm’s argument is largely undisputed. Some skeptics may say that they cannot envision such a concept, but if they do then there is cause to question their sincerity because most people are, at minimum, familiar with the concept of an all-powerful, all-knowing God. And even if you doubt the existence of such a god, it is difficult to imagine someone not being able to envision or understand the concept.

Once it is admitted that a being “greater than which cannot be thought of” exists at least in the mind, Anselm argues that such a thing must necessarily exist in reality, too. Why? Because a being “greater than which cannot be thought of” cannot be understood to exist only in thought, “for if it exists in thought alone, then that than which greater cannot be thought turns out to be that than which something greater can actually be thought” because that which exists in both thought and reality is greater than that which exists in thought alone. In other words, what exists in the mind may be great, but it cannot be said to be as great as something that exists in both the mind and in reality, too. Thus, for something to be the greatest possible thing, it cannot be limited to existing solely in the mind.

Using Anselm’s example from the Proslogion, before a painter paints it, a painting does not exist in reality but only in the painter’s mind. To say it the other way, the painting does exist in the painter’s mind even if it does not exist in reality at the point in time that the painter envisions the painting but before he paints it. But which is greater: a painting that exists only in the painter’s mind or the painting when it has been painted and exists in reality in addition to the painter’s mind? To Anselm, the answer is obvious: the painting that exists in reality in addition to the painter’s mind is greater than the painting that exists only in the mind of the painter. After all, that which exists on two levels of existence is obviously greater than that which exists only in one.

Anselm continues: That which exists in reality is greater than that which exists only in the mind. A being “greater than which cannot be thought of” cannot exist only in the mind or else that which exists in the mind and in reality must be greater than it. Therefore, a being “greater than which cannot be thought of” must exist in reality as well as in the mind.

Breaking this down into a syllogism which I will acquire from ”Twenty Arguments for the Existence of God” by Peter Kreeft and Ronald K. Tacelli.

1. It is greater for a thing to exist in the mind and in reality than in the mind alone.
2. "God" means "that than which a greater cannot be thought."
3. Suppose that God exists in the mind but not in reality.
4. Then a greater than God could be thought (namely, a being that has all the qualities our thought of God has plus real existence).
5. But this is impossible, for God is "that than which a greater cannot be thought."
6. Therefore God exists in the mind and in reality.

If this is troubling to you, you are not alone. Early on, Gaunilo read the Proslogion and argued that Anselm was making a serious error because his argument suggests that if we can imagine a perfect thing, then it must exist in reality which is plainly nonsense. He used the example of a perfect island:

For example, they say there is in the ocean somewhere an island which, due to the difficulty (or rather the impossibility) of finding what does not actually exist, is called "the lost island." And they say that this island has all manner of riches and delights, even more of them than the Isles of the Blest, and having no owner or inhabitant it is superior in the abundance of its riches to all other lands which are inhabited by men. If someone should tell me that such is the case, I will find it easy to understand what he says, since there is nothing difficult about it. But suppose he then adds, as if he were stating a logical consequence, "Well then, you can no longer doubt that this island more excellent than all other lands really exists somewhere, since you do not doubt that it is in your mind; and since it is more excellent to exist not only in the mind but in reality as well, this island must necessarily exist, because if it didn't, any other island really existing would be more excellent than it, and thus that island now thought of by you as more excellent will not be such." If, I say, someone tries to convince me though this argument that the island really exists and there should be no more doubt about it, I will either think he is joking or I will have a hard time deciding who is the bigger fool, me if I believe him or him if he thinks he has proved its existence without having first convinced me that this excellence is something undoubtedly existing in reality and not just something false or uncertain existing in my mind.

I find myself initially in agreement with Gaunilo. After all, if you were to try to convince me that a perfect island existed because you can conceive of it in your mind (an island “greater than which cannot be thought”), I would agree that I would be a fool to believe in its existence just because it can be imagined. But this counter-example does not slow up Anselm in the least. He simply points out that his argument can only apply to a necessary being.

. . . You often picture me as offering this argument: Because what is greater than all other things exists in the understanding [mind], it must also exist in reality or else the being which is greater than all others would not be such. Never in my entire treatise do I say this. For there is a big difference between saying "greater than all other things" and "a being greater than which cannot be thought of." If someone says "a being greater than which cannot be thought of" is not something actually existing or is something which could possibly not exist or something which cannot even be understood, such assertions are easily refuted. For what does not exist is capable of not existing, and what is capable of not existing can be thought of as not existing. But whatever can be thought of as not existing, if it does actually exist, is not "a being greater than which cannot be thought of." (Emphasis added.)

This is difficult language. It has to do with the difference between contingent beings and necessary beings. A being which can be thought to not exist is a contingent being. But a being who must necessarily exist is a necessary being. Anselm is arguing that the example of the island does not fit his example because the island is not a necessary being. However, if there is a being who is the greatest of all possible beings, that being must be necessary, too.

John DePoe sums it up nicely.
The reply Anselm gave to Gaunilo seems to clarify how his ontological argument follows. Anselm replied that his proof uniquely applies to God for only a necessary being would have the greatest conceivable existence. For any given island, there can always be a better one. For example, consider the existence of the tallest possible man in Manhattan. No matter how tall you imagine one man, it is always possible to imagine another man at least an inch taller. Thus, it is nonsense to speak of the tallest possible man in Manhattan, and this conclusion will be the case for all finite and material beings. God is exempt from this fallacy because he has necessary existence and would qualify as the greatest of all possible beings. So, Anselm's argument remains unscathed by Gaunilo's criticism.

John DePoe, "The Ontological Argument"

Difficult? Yes, it is. But this ontological argument is very compelling to those who accept a more Platonic approach to the world. As such, it is well worth the time to familiarize yourself with it so that you can be prepared to give a defense of your faith in all circumstances –- even when confronted by people who hold a very philosophic approach to the world. For more, visit the CADRE Ontological Argument page (under construction).

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