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The Ontological Argument for God’s Existence

If there’s one argument for the existence of God that is full of chutzpah, it’s this one

Trent Horn

Chutzpah is a word that comes from the Hebrew hutspa that refers to a kind of audacious courage or a reckless self-confidence. It can be a complement or an insult, depending on the context of how it’s used. Either way, if there’s one argument for the existence of God that is full of chutzpah, it’s the ontological argument.

What is ontology?

Ontology refers to the study of being, and so the ontological argument claims that God is the kind of being who simply must exist; therefore, he does exist. Most arguments for God’s existence start from something we observe in the world and then logically infer God as the cause of these observable effects (e.g., the universe, morality, well-ordered laws of nature). But the ontological argument starts not with what we observe but with the very idea of God itself and says that this idea entails that God must actually exist.

As my friend Jimmy Akin once put it, “Instead of being too good to be true, God turns out to be too good not to be true.”

The argument’s origin can be found in the writings of the eleventh-century saint and Doctor of the Church St. Anselm of Canterbury. Anselm started with the idea that God is “that which nothing greater can be conceived.” If you think God is just a powerful creator of the universe who was made by some other God, then what you’re thinking of isn’t God, because there is something greater than it (i.e., the God that made this god).

So, now that we understand God is “that which nothing greater can be conceived,” what follows from this definition? Well, God must have all power, all knowledge, and all forms of goodness. Anselm says:

If that than which nothing greater can be conceived exists in the understanding alone, the very being than which nothing greater can be conceived is one than which a greater can be conceived. But obviously this is impossible. Hence, there is no doubt that there exists a being than which nothing greater can be conceived, and it exists both in the understanding and in reality.

Anselm is saying that if you imagine the concept of God in your mind, that’s not really God, because there is something “greater” than a God that exists only in your mind: a God that exists in reality too. Therefore, since God is “that than which nothing greater can be conceived,” and a God that exists in reality as well as the mind is greater than a God that exists only in the mind, it follows that God exists.

Like I said, it’s got chutzpah.

Too good to be true?

Most people, even if they believe in God, suspect there’s something wrong with this deceptively simple argument. But merely suspecting an argument is unsound is not enough to demonstrate that it is unsound. The twentieth-century atheist philosopher Bertrand Russell accepted the argument at first, saying, “Great God in Boots!—the ontological argument is sound!”

He eventually abandoned faith in the argument, but in doing so he noted “the argument does not, to a modern mind, seem very convincing, but it is easier to feel convinced that it must be fallacious than it is to find out precisely where the fallacy lies.”

One of Anselm’s contemporaries, a monk named Gaunilo, tried to demonstrate this fallacy, or error in reasoning, by parodying the argument in order to show its absurdities (a technique we now call reductio ad absurdum). Gaunilo said that one could conceive of an island “than which none greater can be conceived” but it wouldn’t follow that such a perfect island actually exists. Modern atheists often resort to a variant of Gaunilo’s reply by saying that the ontological argument could be used to prove absurdities like a “maximally great pizza” must exist.

But this actually isn’t a fatal objection to Anselm’s argument.

Unlike the idea of God, perfect islands and maximally great pizzas are incoherent ideas that can’t exist in reality, so we can’t even really conceive of them in the mind. In a debate with the late atheist Victor Stenger, Christian theologian William Lane Craig noted that a “maximally great pizza” is incoherent because an object isn’t a pizza if it can’t be eaten, and if such an object can be eaten, then it wouldn’t be “maximally great,” since that kind of greatness includes necessary existence (“Eating Victor Stenger’s Ontological Pizza,” YouTube.com).

Moreover, an island could always have one more coconut tree, and a pizza could always have one more topping, to make it “greater.” This means there is no island or pizza “than which nothing greater can be conceived.” But there could be a being “than which nothing greater can be conceived” because it had complete possession of what philosophers call “great-making properties”—such as power, knowledge, and existence—that have intrinsic maximums.

Unlike perfect islands and pizzas, we can imagine a perfect being that has all knowledge, can do anything that is possible, and exist in all circumstances, because these attributes (unlike the ones that make islands or pizzas great) have intrinsic maximums. But if that’s the case, why don’t most philosophers (including theists) accept Anselm’s argument?

St. Thomas Aquinas said that since we don’t have direct knowledge of God’s essence (or what he’s like), we must reason to God’s existence (which just is his essence) from what we observe, and so we can’t have self-evident knowledge that God exists, even through Anselm’s argument (Summa Theologiae, q. 2, art. 1).

German Enlightenment philosopher Immanuel Kant’s criticism is the more common one today and relies on the idea that existence is not a “predicate” or an attribute that makes something “great.” Instead, existence is the precondition for a being to be great at all, and so it has to be independently supported beyond a being’s definition. Russell made a similar criticism when he said ontological arguments are merely examples of “bad grammar.”

Modal logic to the rescue

In the twentieth century, some philosophers of religion tried to rehabilitate Anselm’s argument using a tool of reasoning called modal logic.

Modal logic is a system that helps us understand concepts such as necessity and possibility. If something is necessary, then it has to be or there can be no world without that thing. If something is possible, however, that simply means it can be.

So, for example, using modal logic, we would say that if something is necessary, then it is also possible. If it has to be, then it can be. Another way to understand this kind of logic is through the language of “possible worlds.”

The actual world is the universe or reality in which you and I currently exist. A “possible world” is just an alternative way to describe the actual world that never actually happened. For example, in another possible world you never read this article, or I never wrote it, or I never even existed.

While some philosophers speak of possible worlds as if they were real, existing things (sort of like parallel dimensions), most people understand this as just the language of possibility. We use the language of “possible worlds” to talk about how things could have been.

But when we do that, we notice that some things are constant, no matter what possible world we talk about. For example, no matter what possible world we can conceive, two plus two always equals four. We say these truths are necessary, or that they exist in every possible world.

Okay, so maybe there are truths that exist in every possible world, but could there be a being that exists in every possible world, or a necessary being?

Some philosophers have used modal logic and its notions of “necessity” and “possibility” to get around Kant’s criticisms of the ontological argument. The most famous of these is Alvin Platinga’s argument that a “maximally great being” must exist. William Lane Craig summarizes Plantinga’s argument this way:

  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.

Therefore, a maximally great being exists.

Is God even ‘possible’?

If it is possible God exists, then God must exist in some possible world or description of reality. But if God exists in one possible world, then he must exist in every possible world—because God, by definition, exists in all logically possible circumstances. But the actual world is a possible world, albeit one that actually came about, so that means God exists in this world too. Therefore, God exists.

It may surprise you to learn that most philosophers think Plantinga’s argument is valid, meaning it doesn’t have any logical errors. According to atheist Arnold Guminski:

It is generally agreed that the [argument] is formally valid. And I think that it is fairly obvious (assuming that a maximally great being is defined as a maximally excellent being that exists in every possible world) that if a maximally great being exists in some possible world, then that being exists in all possible worlds and therefore in the actual world (infidels.org/library/modern/ arnold_guminski/plantinga.html).

The weakness of the argument lies in the first premise, namely, “It is possible that a maximally great being exists.” If this means hypothetically possible (or, “for all we know”), then the argument doesn’t really prove anything, since it’s also hypothetically possible that a maximally great being exists in no possible world, and such a premise could be used to form a valid “anti-ontological argument” against God’s existence.

But if it means metaphysically possible, in the same way it’s possible the roulette table could have landed on black instead of red, then we need some reason to believe God’s existence is a real possibility. That’s why most philosophers have tried to show that a thing such as a universe that requires an explanation for its existence naturally leads to at least the possibility of God’s existence.

For example, the philosophers Brian Leftow and Alexander Pruss believe the ontological argument can be strengthened by noting that people’s experience of God supports the premise that God is a real possibility, since people don’t have experiences of logically impossible things such as square circles.

But when philosophers appeal to these experiential reasons to support God’s existence, they’re no longer making a purely ontological argument for God’s existence based solely on proving God exists from the idea of God alone. This may be why Plantinga wrote, “They cannot, perhaps, be said to prove or establish their conclusion. But since it is rational to accept their central premise, they do show that it is rational to accept that conclusion” (The Nature of Necessity).

Personally, I don’t use the ontological argument when I evangelize atheists, because most people think it’s just some kind of semantic trick and so are already antagonistic about it. I agree with Plantinga that it isn’t a classical proof for the existence of God.

However, people have a wide variety of intellects and imaginations, and so I believe the argument may be helpful for certain people who are open to this way of thinking about the issue.

In that respect, the ontological argument is similar to another “unusual argument” for the existence of God from Peter Kreeft:

There is the music of Johann Sebastian Bach.
Therefore there must be a God.
You either see this one or you don’t.

When it comes to modern versions of the ontological argument for the existence of God, I agree: you either see this one or you don’t.

Sidebar: Ontology à la Descartes

The philosopher René Descartes (1596-1650) proposed his own version of the ontological argument, based not on the idea of God entailing God’s existence but on the impossibility of a finite mind coming up with such an infinite idea in the first place. Peter Kreeft and Ronald Tacelli summarize Descartes’s argument this way:

“We have ideas of many things. These ideas must arise either from ourselves or from things outside us. One of the ideas we have is the idea of God—an infinite, all-perfect being. This idea could not have been caused by ourselves, because we know ourselves to be limited and imperfect, and no effect can be greater than its cause. Therefore, the idea must have been caused by something outside us which has nothing less than the qualities contained in the idea of God. But only God himself has those qualities. Therefore, God himself must be the cause of the idea we have of him. Therefore, God exists.”


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