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What Is the Ontological Argument for God’s Existence?

When it comes to modern versions of the ontological argument, you either see it or you don’t

Trent Horn

Chutzpah is an English word that comes from the Hebrew hutspa, which refers to a kind of audacious courage or a maddeningly reckless self-confidence. It can be a complement or an insult depending on 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.

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

As was pointed out recently in this space, the argument’s origin can be found in the writings of the eleventh century saint and doctor of the Church, Anselm of Canterbury. Anselm started with the idea that God is “that, than 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, than 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, than 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 then goes on to say:

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, then that’s not really God because there is something “greater” than a God that only exists 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, at least it’s got chutzpah.

Most people, even if they believe in God, suspect there’s something wrong with this deceptively simple argument.

One of Anselm’s contemporaries, a monk named Gaunilo, tried to refute the argument by parodying it in order to show its absurdities (a technique called reductio ad absurdum). He 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, 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.

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 would have complete possession of what philosophers call “great-making properties” like power, knowledge, and existence that have intrinsic maximums.

Unlike perfect islands and pizzas, we can imagine a perfect being that just 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, then why don’t most philosophers (including theists) accept Anselm’s argument?

Aquinas said that since we don’t have direct knowledge of God’s essence (or what he’s like) this means 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). 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.

In the twentieth century some philosophers used modal logic and its notions of “necessity” and “possibility” to get around Kant’s criticism. 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.
  6. Therefore, a maximally great being exists.

The actual world is the universe or reality in which you and I currently reside. A “possible world” is 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 you and I never existed.

If it is possible that 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 that world too. Therefore, God exists.

It may surprise you to learn that most philosophers think Plantinga’s argument is valid, or it doesn’t have any logical errors in it. 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.

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 ball 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 a that things like a universe that requires an explanation for its existence naturally leads to at least the possibility of God’s existence. 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 like square circles.

But when philosophers appeal to these experiential reasons to support God’s existence then 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 even Plantinga himself said, “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.”

I don’t use the ontological argument when I evangelize atheists because most people think it’s just some kind of semantic trick so they already have an antagonism against it. I also 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, I agree: you either see it or you don’t.

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