Excursus on Natural Theology (Part 22): The Ontological Argument

The Ontological Argument

In our excursus on natural theology we’ve talked about a number of arguments for God’s existence such as the argument from contingency, the kalam cosmological argument, the argument from the fine-tuning of the universe, the argument from the applicability of mathematics, and the moral argument. Today we turn to a new argument (and the last that we’ll be surveying in our class), and this is the ontological argument for God’s existence.

In the year 1078 a Benedictine monk by the name of Anselm, who later became the Archbishop of Canterbury, formulated a new and bold argument for the existence of God which has now fascinated philosophers for nearly a millennium. A year earlier in 1077 Anselm had finished writing a treatise called the Monologium in which he presented cosmological and moral arguments for God’s existence. But Anselm was dissatisfied with the complexity of the case for theism that he had developed, and he wanted to find a single argument which would prove that God with all of his attributes, in all of his greatness, exists. He had pretty much given up on the task when he came upon the definition of “God” as (in Latin) aliquid quo nihil maius cogitari potest. The Latin is so great. You can learn this phrase and impress your friends when they ask you for a definition of God! God is something than which nothing greater can be conceived, or, in more idiomatic English, God is the greatest conceivable being.

Anselm argued in his treatise that followed – the Proslogium - that once you understand the definition of God, once you understand what God is, then (if you’ve really understood it) you will see that God must exist because if God did not exist he would not be the greatest conceivable being. A greatest conceivable being must be an existent being. Otherwise it wouldn’t be the greatest. So God’s existence is inconceivable for anybody who really understands the word “God” and understands what God is.

Anselm says that’s why Psalm 14:1 says, “The fool has said in his heart there is no God” – because if that person really understood the word “God,” then he would see that God must exist. So he is a fool for saying that the greatest conceivable being does not exist.

Anselm’s argument came to be known as the ontological argument, which is from the Greek word ontos, meaning “being.” It went on to assume a variety of different forms and has been defended by some of the greatest thinkers in the history of philosophy, for example, John Duns Scotus, Rene Descartes, Benedict de Spinoza, Gottfried Wilhelm Leibniz, and so on.

What is the common thread in all of these different versions of the argument that unites them and makes them ontological arguments? I think the common thread among these various ontological arguments is that they all try to deduce the existence of God from the very concept of God, together with some necessary truths. Proponents of the ontological argument in its various forms maintain that once we understand what God is (once you have an adequate conception of God – whether the greatest conceivable being, or the most perfect being, or the most real being) then we will see that such a being must in fact exist.

This argument has tended to sharply polarize philosophers. For example, the 19^th century German philosopher Arthur Schopenhauer characterized the ontological argument as “a charming joke.” That opinion is certainly shared by many other philosophers today. On the other hand, the argument has been taken very seriously and in fact defended as sound by quite a number of 20^th century philosophers who are of some prominence as well, notably Norman Malcolm, Charles Hartshorne, and Alvin Plantinga.

Since Plantinga’s version of the argument is, I think, the most sophisticated and the most recent development of the argument, we’ll use it as the springboard for our discussion of the ontological argument. In Plantinga’s version of the argument he appropriates the insight of Gottfried Wilhelm Leibniz that the ontological argument assumes that the concept of God is possible. That is to say, the argument assumes that the concept “God” or “the greatest conceivable being” is a coherent concept. Or, using the semantics of possible worlds, it assumes that there is a possible world in which God exists.

For those who are unfamiliar with the semantics of possible worlds, let me just say a word of explanation about this, lest we be misled. When we talk about possible worlds, we do not mean planets or even other universes. Rather, a possible world is simply a maximal description of reality. It is a way reality might be. I think the easiest way to think about a possible world is as a huge conjunction of propositions – p and q and r and s and so on, that are mutually consistent. These individual conjuncts (p, q, r, s) are propositions which can be true or false. A possible world is a consistent conjunction which comprises every proposition or its contradictory so that it yields a maximal description of reality. Nothing is left out of such a description. By negating different conjuncts or propositions we can arrive at different possible worlds. So, for example, we could call W1 this description of the world:

W1 = p & q & r & s . . .

But other descriptions of the world could be:

W2 = p & not-q & r & not-s . . .

W3 = not-p & q & not-r & s . . .

W4 = not-p & not-q & r & not-s . . .

And so on.

Only one of these descriptions will be comprised of propositions or conjuncts all of which are true and so is the true description of the way reality actually is. That description we will dignify by saying it is the actual world. One of these will have all true conjuncts, and that will be the actual world.

When we talk about possible worlds, these propositions making up these various conjunctions need to be not only compossible (that is to say, be possible together) but each proposition individually needs to be possible as well. For example, take the proposition, “The prime minister is a prime number.” That proposition isn’t even possibly true. The prime minister is a concrete object – a flesh and blood human being. Therefore it is impossible that he could have been a prime number. That means that no possible world will include that statement as one of its conjuncts because it is impossible. That will be false in every possible world. It is necessarily false. So a proposition which is necessarily false will be one that is false in every possible world.

By contrast, the proposition, “George McGovern is the President of the United States” is false in the actual world. But there are possible worlds in which it is true. McGovern could have been elected President of the United States. So that is a possible proposition, and it will be a conjunct in some possible worlds. To say that McGovern is the President of the United States in some possible world is simply to say that there is a maximal description of reality that has that relevant proposition as one of its conjuncts. That isn’t the actual world. That would be a non-actual possible world – a possible world which isn’t actual, one in which that conjunct is true.

Leibniz’s insight into the ontological argument is that the argument assumes that the proposition “God exists” or “A greatest conceivable being exists” or “A perfect being exists” is possibly true. That is to say that God exists in some possible world. In some possible world that statement, that conjunct – “God exists” or “A maximally great being exists” or “A perfect being exists” – that proposition is true in some possible world.

If the concept of God is incoherent or impossible, then God would be like that prime minister that is a prime number. It would be a metaphysical impossibility. He would not exist in any possible world. The word “God” in that case would refer to nothing, no more than the words “a square circle” refers to something. In both cases the words “A greatest conceivable being” or “a square circle” would just be an incoherent combination of words. They don’t refer to anything. As Leibniz says, the ontological argument assumes that the concept of God is a coherent concept – it is possible for God to exist.

In his version of the argument, Alvin Plantinga conceives of God as a being which is maximally excellent in every possible world. What does he mean by that? By maximal excellence, Plantinga takes this to entail such excellent-making properties as being all-knowing, all-powerful, and all-good. A being which has those properties will be more excellent than a being which is limited in knowledge or strength or goodness. So a maximally excellent being will be one that has omnipotence, omniscience, and moral perfection.

A being which has maximal excellence in every possible world has what Plantinga calls maximal greatness. There is a difference between maximal greatness and maximal excellence. Maximal excellence is the property of being all-knowing, all-powerful, all-good. Maximal greatness is the property of having maximal excellence in every possible world.

Now, Plantinga says, the property of maximal greatness is possibly exemplified. That is to say, this is a coherent concept. There is a possible world in which a maximally great being exists. But if a maximally great being exists in one possible world, it exists in all of them, including the actual world. Therefore, God exists.

We can formulate Plantinga’s version of the ontological argument as follows:

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

2. If it is possible that a maximally great being exists, then a maximally great being 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.

6. Therefore, a maximally great being exists.

Although Plantinga thinks that the ontological argument is a sound and non-question begging argument for God’s existence, initially at least he did not regard it as a “successful piece of natural theology.” Why not? Why isn’t this a successful piece of natural theology? He said it is because the key premise, “It is possible that a maximally great being exists” can be rationally denied.

But Plantinga later confessed that he had set the bar for “success in natural theology” unreasonably high. This is what he later came to say,

I employed a traditional but wholly improper standard: I took it that these arguments are successful only if they start from propositions that compel assent from every honest and intelligent person and proceed majestically to their conclusion by way of forms of argument that can be rejected only on pain of insincerity or irrationality. Naturally enough, I joined the contemporary chorus in holding that none of the traditional arguments was successful. (I failed to note that no philosophical arguments of any consequence meet that standard; hence the fact that theistic arguments do not is of less significance than I thought.)[1]

So Plantinga says he initially thought that in order to be a successful piece of natural theology the arguments had to compel assent from any rational person. He came to see that if you hold that standard, then there are no good philosophical arguments for anything. Plantinga now believes, “The ontological argument provides as good grounds for the existence of God as does any serious philosophical argument for any important philosophical conclusion.”[2] George Mavrodes, who was a professor of philosophy at the University of Western Michigan, rightly remarked on Plantinga’s assessment, “But if natural theology can be that good, as good as the best arguments anywhere in serious philosophy, . . . why should we not put forward these powerful arguments as proofs of God?”[3]

You might be surprised to learn that premises (2) through (5) of this argument are relatively uncontroversial. The real point of contention is premise (1) – that it is possible that a maximally great being exists. This is the principal question which needs to be settled with regard to Plantinga’s version of the ontological argument. What warrant exists for thinking that this key premise “It is possible that a maximally great being exists” is true?

In dealing with this issue it is very important that we keep firmly in mind the difference between what we could call epistemic possibility and metaphysical possibility. “Epistemic” derives from the Greek word episteme or “knowledge.” Epistemic possibility indicates what is possible with respect to your knowledge. So, in response to the ontological argument’s key premise, one is tempted to say, “Well, it is possible that God exists, and it’s possible that God does not exist.” That is true only with respect to epistemic possibility. What you are saying there is: “For all I know, God exists or he doesn’t exist. It is possible with respect to what I know. It is epistemically possible. I don’t know which is right. For all I know, God may or may not exist.”

But metaphysical possibility has to do with what is actualizable or what can be real independently of what you think about it. If God is a maximally great being, then his existence, if it is metaphysically possible, will be metaphysically necessary. It will not be true to say it is possible that God exists or it is possible that he doesn’t. That would be to say that God exists in some possible worlds, but he doesn’t exist in other possible worlds. That would be incorrect. The concept of a maximally great being is such that it either exists in all possible worlds or it exists in none of them. But you can’t say it exists in some of them and does not exist in others of them.

Let me give an illustration of this difference between epistemic possibility and metaphysical possibility that will help to make the point clear.

There is a mathematical proposition known as Goldbach’s Conjecture that remains unproven in mathematics today. Goldbach’s Conjecture says that every even number greater than 2 can be expressed as the sum of two prime numbers. So take any even number greater than 2, like 10 – that will be equal to the sum of two prime numbers, in this case 7 and 3. Although Goldbach’s Conjecture has been tested to enormous lengths, no mathematician has ever been able to prove it or disprove it. We don’t know whether Goldbach’s Conjecture is true or not. So in this epistemic sense one can say (epistemically) Goldbach’s Conjecture could be true or it could be false. We just don’t know which. But as a piece of mathematics, Goldbach’s Conjecture is either necessarily true or necessarily false. It is either necessary that Goldbach’s Conjecture is true or it is impossible that it is true. It cannot possibly be true and possibly be false in this metaphysical sense. It is either impossible or necessary. One or the other. But it cannot be both possibly true and possibly false. It is necessarily true or necessarily false.

In the same way, although the key premise of the ontological argument could be epistemically uncertain – we don’t know whether it is possible that a maximally great being exists or not – nevertheless, the epistemic entertainability of the key premise or of the denial of the key premise doesn’t guarantee that either is metaphysically possible.

The question we are asking here is: is it metaphysically possible that a maximally great being exists? Not is it epistemically possible, which I think it certainly is. But is it metaphysically possible?

Think about it – the concept of a maximally great being seems intuitively-speaking a coherent idea and therefore possibly instantiated. The idea of a being which is all-knowing, all-powerful, all-good in every possible world seems to be a perfectly coherent idea and therefore possibly instantiated. In order for the ontological argument to fail, the concept of a maximally great being would have to be logically incoherent. It would need to be like the concept of a married bachelor. The concept of a married bachelor, when you think about it, is not a strictly or explicitly self-contradictory concept as would be, say, the concept of a married unmarried man. That would be strictly contradictory. But nevertheless once you understand the concept or the meaning of what a bachelor is you can see that it is impossible that there could be something corresponding to that concept – that that concept could be possibly exemplified or that property possibly instantiated. By contrast to that, the concept of a maximally great being doesn’t seem at all incoherent. Quite the contrary, it seems perfectly coherent to talk about a being which is maximally excellent in every possible world. That would go some distance, I think, to warrant the first premise that it is possible that a maximally great being exists.