by Luke Wayne


The ontological argument for the existence of God is a classical Christian argument that contends that the very concept of God logically and necessarily demands existence. It is the argument that, if one understands what is meant by the word “God” and follows it out to the logical conclusion, it is impossible for such a being not to exist. Imagining God to not exist is like imagining a five sided triangle. Once you grasp the meaning of “triangle”, you realize that this is absurd. If the shape you are imagining can have five sides, you are not imagining a triangle. The concept of “triangle” demands three sides. Similarly, if you are imagining a being that might or might not exist, you are not imagining God, because the very concept of God demands existence.

Think about the concept of “truth” for a moment. Truth simply has to exist. Some people claim that there really is no truth, but they simply have not followed it through. If I say, “there is no truth”, I am saying something plainly absurd. If the statement is true, then it is a truth and truth exists. If the statement is not true, then it is untrue that truth does not exist, and therefore truth exists. The very concept of truth demands existence just as plainly as the very concept of a triangle demands three sides. The Ontological argument insists that God’s existence is necessary in this same way. The very concept of God simply demands existence.

The Argument

This argument was first attempted by Anselm of Canterbury in the 11th century. He approached it this way:

  1. God is by definition the greatest conceivable being.
    1. This is obvious, because if one can conceive of a being greater than God, then that being would be God
  2. If God exists only in the mind, something greater than God can be conceived: A God who exists in the actual world
  3. But God is the greatest conceivable being, so definitionally we cannot conceive of anything greater than God
  4. God must, then, be a being that exists not only in the mind but also in reality
  5. Therefore God exists

Anselm explained this another way, saying:

1. A being whose non-existence is inconceivable is greater than a being whose non-existence is conceivable.

2. God is the greatest conceivable being

3. God, then, is a being whose non-existence is inconceivable

4. Therefore, God exists

Many Christian thinkers still believe in and use various forms of this kind of argument. The most popular modern expression was published by Alvin Plantinga and popularized by William Lane Craig. It follows the approach of Anselm in using the concept of God’s definitional greatness, and frames the argument this way:1

1. It is possible that a maximally great being exits.

2. If a maximally great being exists, then it exists in some possible world.

3. If a maximally great being exists in some possible world, then it exists in every possible world

4. If a maximally great being exists in every possible world, then it exists in the actual world

5. If a maximally great being exists in the actual world, then a maximally great being exists

5. Therefore, a maximally great being exists

In this version, one begins by noting that it is logically possible for there to be a greatest conceivable being (or “maximally great” being) which is what we mean by “God”. If that is true, then there is at least one logically possible way the universe could be (or “possible world”) in which the greatest conceivable being exists. But, by definition, the maximally great being must exist in all possible worlds or he would not be maximally great. Therefore, since he does exist in a possible world, by definition he exists in every possible world, which means he exists in the real world. In other words, unless the concept of God is completely incoherent, God logically must exist.

Common Objections

The ontological argument is often laughed off by Christians and atheists alike, but when seriously engaged has proven more difficult to shoot down than it initially appears. The argument appears logically valid, in that its conclusion does follow properly from its premises. The primary objection has been that it could be used to justify all kinds of mythical things. One of Anselm’s own 11th-century opponents named Guanilo, in his work “On Behalf of the Fool,”2 argued this point, using the example of proving “the greatest conceivable island.” The problem with this kind of objection is that it either equivocates on the definition of “great” or else it places an arbitrary limitation by insisting it be an “island”.

When we speak of something like an island being “great”, we are not typically talking about objective greatness in the very nature of its being. We usually mean a more subjective idea of greatness. The island is “great” because of the things about it that are pleasurable to me; it’s beautiful beaches, delicious tropical fruits, and pleasant climate, for example. That is obviously not what is meant by “greatness” in the Ontological argument. God is not “great” because of the things I happen to like about Him. God’s greatness is the objective superiority of His being, whether I like it or not. One simply cannot think of something like an island possessing this kind of objective greatness. The idea simply doesn’t make sense. Islands are very dependent things. They require the existence of oceans and sand and natural forces to even exist. Whatever form of greatness an island has is derived from other things. The very definition of “island” insists on it lacking the kind of greatness we are talking about. The very idea of “island” is contrary to the idea of being logically necessary. The concept of God demands existence, but the concept of island demands that it may or may not exist depending on other factors. These caricatures, therefore, do not actually challenge the logic of the argument.

Some have tried to show the argument to be self contradictory, such as by challenging, “wouldn’t a God who can prove the ontological argument false be greater than a God who can’t prove the Ontological argument false?” The problem here, of course, is that God proving the Ontological argument false would only be great if the Ontological argument actually is false. Proving true things false is not part of anyone’s definition of greatness or perfection, much less the definition of God.

Which God?

While the word “God” or “god” is used in a variety of ways and for a variety of false deities, the Ontological argument is clearly using “God” in a strict and specific sense of the word that is generally understood by most people. It is talking about the one, singular being that is above and beyond all else, the being that must exists while other beings may not. It is a strictly monotheistic argument. Neither pagans, Hindus, nor Mormons receive any help from this argument. Indeed, the argument only allows for one particular God, the God who is objectively greater than everything else. It is no stretch to say that this argument contends only for the God of Christianity. By way of one example, think on the triune nature of God. C.S. Lewis astutely noted:

“A good number of people nowadays say, ‘I believe in a God, but not in a personal God.’ They feel that the mysterious something which is behind all other things must be more than a person. Now the Christians quite agree. But the Christians are the only people who offer any idea of what a being that is beyond personality might be like. All the other people, though they say that God is beyond personality, really think of Him as something that is impersonal: that is, as something less than personal. If you are looking for something super-personal, something more than a person, then it is not a question of choosing between the Christian idea and the other ideas. The Christian idea is the only one on the Market”3

The Christian God is uniquely supreme, having within His own nature fellowship and love, authority and submission. A God who, even without creation, is to Himself “I” and “You” and “We” and “They”. One supreme and perfect being who is three distinct persons. Whether one considers the ontological argument to be a good one or not, it is no real wonder that it has always been almost exclusively a Christian argument.

Strengths of the Argument

Unlike many arguments, the ontological argument argues from God rather than to Him. It is rooted in the very nature of God and is therefore specific to the true and living God rather than to the general idea of an ultimate principle or divine being. It does not present God as something that might or might not exist and that we need to prove one way or the other. It also is not rooted in probability. If the argument is right, it is wholly right. It does not show God to be more likely to exist, but rather insists that He must exist. It therefore takes the person out of the position of judging what is true and places them in the position of responding to the truth.

Weaknesses of the Argument

The argument is very confusing to many. Worse, it can also come off as more of a semantic game or word-play rather than a serious argument. Even many Christians find it both unpersuasive and unhelpful.

1. William Lane Craig, Reasonable Faith: Third Edition (Crossway Books, 2008) 184-185
2.Psalm 14:1 says that “the fool says in his heart ‘there is not God’. This is the “fool” Guanilo was speaking up for in writing against Anselm’s argument”
3. C.S. Lewis, The Complete C.S. Lewis Signature Classics (HarperCollins, 2002) 88