The ontological argument for God's existence has taken several different forms throughout history, but the most popular version is probably that of the 11th century philosopher and theologian Saint Anselm of Canterbury. Anselm argued that there has to be a being greater than anything else we can conceive of, and he called this being God (1). He also went on to argue that this being cannot solely exist in the imagination, since an even greater being would be one that exists in reality and is not dependent on our conception of it. All ontological arguments deal with the human capacity to perceive God and reason for the existence of God, but if God is truly above the ways of man - as many theists claim - then exactly how successful can these assertions be?

I. How Great Can God Be?

The Bible, the Quran, the Tanakh, and many other religious texts all give indication that their god is the most inconceivably powerful and limitless being that one can ever think of. For God, "all things are possible" (Matthew 19:26) and it would be quite heretical to think there is a being that can excel God in any way. This is the grounding for Anselm's argument, that God is the mack daddy of all possibilities. No one really wants to believe their fate is in the hands of an impotent god.

However, in trying to imagine the greatest being possible, we might run into a few problems. If God is the greatest conceivable being in all ways, he must literally excel at every scenario we lowly humans can conceive of. Here is where I would object to Anselm's argument that a god which exists in reality is greater than one which exists only in our minds. Would it not be some incredible feat for a god to interact with our universe while simultaneously not existing? A non-existent entity being able to act as an extant entity seems like it would be great and powerful indeed.

Already we have imagined a being greater than Anselm's "greatest" being. If we are simply concerned with the greatest extent of this being's abilities, properties, and power, then many problems present themselves. Can God make a rock so heavy that he himself cannot lift it? The common objection is that God cannot act against his own nature or against his own power, but this claim makes tremendous assumptions about God - assumptions that rarely even find scriptural support. A god that chooses to restrict its own power and behavior is still limited.

Ultimately, the prominent error in Anselm's ontological argument is the subjectivity of greatness. He argues in chapter three of his Proslogion that it is greater for a being to be necessary than contingent, yet in what sense is it greater and how can we possibly know if this is true? As I already stated, I believe it would be a greater feat for God to be non-existent and still work through our world than it would be for him to exist and just behave naturally. Would it be a logical contradiction? Not for God, in whom all things are regarded as possible.

II. I Think, Therefore God Exists

The next formulation of the ontological argument that often arises in conversation is the version introduced by French philosopher René Descartes in the 17th century. In his Fifth Meditation, Descartes writes:

Descartes is making two important claims here: first, that whatever he can conceivably associate with the idea of something is true of that thing - and second, that since he thinks of necessary existence in association with the idea of God, then God must exist. Despite what Descartes may be convinced of, not everyone can so clearly and distinctly picture a supremely perfect being or a necessary being as they can a shape or a number. Different people can have very different concepts of God too, such as the ancient Greek pantheists believing their gods to be limited in both knowledge and power, among other things.

Of course, the most apparent objection to Descartes' ontological argument is that our inability to separate one idea from being associated with another idea does not mean that things are the same way in the real world. Even if we pretend that the concept of God does imply necessary existence, we cannot be sure that it is true outside of our own minds. It almost seems as though Descartes is attempting to argue that God's existence is self-evident, which is far from being true for many people (if it were, what is the use of all these "proofs"?).

A priori knowledge is knowledge learned by virtue of its meaning - it is independent of experience. In the 18th century, the philosopher David Hume criticized the suggestion that anything could be proven to exist through an a priori argument:

"1. The only way to prove something a priori is if its opposite implies a contradiction.
  2. If something implies a contradiction, then it is inconceivable.
  3. Everything can be conceived not to exist.
  4. Nothing can be proven to exist a priori, including God." (3)

One needs a reason for assuming that God necessarily exists and for assuming that whatever we imagine to exist must therefore exist. These are not self-evident truths, and it is entirely possible and conceivable that neither of them are true.

III. Kant and Existence

In the 18th century, the German philosopher Immanuel Kant provided his own refutation of the ontological argument in his Critique of Pure Reason (4). Kant basically stated that simply defining what God is does not automatically entail his existence. We can imagine that God has the property of omnipotence or perfection, but existence is not a property. Think of a person and a person that actually exists. There is no difference between the concepts, except for the fact that the person who actually exists can be experienced - we can find out about their location, physical properties, lifespan, etc. Descartes' assertion that a supremely perfect being must exist in order to be a supremely perfect being is erroneous and tautologous in his ontological argument.

The question of God's existence is related to whether our concept of God corresponds with anything in the real world. We say that something exists when we have experience of it in space and time, but it is quite impossible to make such an assertion of God, and it certainly requires some empirical evidence to be even slightly convincing to non-believers. For reasons like these, the several different formulations of the ontological argument fail, as do many of the other arguments for God's existence. They are structured on many assumptions and hypotheticals, rarely even touching on solid ground for the spatio-temporal presence or experience of God that they purport to be demonstrating.

1. Anselm. (1078) Proslogion. Chapter II
2. Descartes, R. (1641) Fifth Meditation. AT 7:65; CSM 2:45.
3. Hume, D. (1779) Dialogues Concerning Natural Religion. Part IX.
4. Kant, I. (1787) Critique of Pure Reason.