The ontological argument for the existence of God is a famous one, being one of the first arguments made. It still exists today in quite a variety of forms.

The first version came from St. Anselm in Proslogion, written in 1078. His argument has a lot of twists and turns about an idea existing in our minds and in reality, but the argument can be neatly summarized without that, as follows:

1. God is defined to be the greatest possible being.
2. Existence is necessary to be the greatest possible being.
3. Therefore from 1 and 2, God exists.

Many philosophers after Anselm continued to shape this argument, but it remained in roughly the same form. Even Descartes in Meditations (1637) used the same argument 500 years later, saying that “God’s perfection logically implies existence the same way two mountains logically imply a valley”.

Nearly a millenium after Anselm, a second version of the argument comes from Alvin Plantinga in The Nature of Necessity, written in 1974. It keeps to roughly the same structure, but also makes use of possible worlds.

4. A possible world is defined to be any world that can be imagined to exist, including our own.
5. God is defined to be the greatest possible being.
6. If a greatest possible being exists in a possible world, it must exist in all possible worlds.
7. The greatest possible being exists in a possible world.
8. Therefore from 4-7, God exists in our possible world.

A Reduction to Absurdity

A few years after Anselm’s argument was published, a monk named Gaunilo (or Gaunilon) of Marmoutier responded to the argument through what is called a reducto ad absurdum (reduction to absurdity), which defeats an argument not by showing that it contains an unsound premise or an invalid conclusion, but by showing that it produces absurd conclusions when applied to different scenarios.

An summary of his argument:

9. The Lost Island is defined to be the greatest possible island.
10. Existence is necessary to be the greatest possible island.
11. Therefore from 9 and 10, the Lost Island exists.
12. Obviously, the Lost Island does not exist.
13. Therefore from 11 and 12, conclusion 3 is invalid.

Initially this seems strange, because what qualities make an island greater than another? Are we to imagine that the Lost Island has the most ideal tropical weather and the best ratio of palm trees to beaches? It seems like for every island we can imagine, we can always imagine a better island. But it seems like if this is the case, then it must also hold true for God: either we can imagine the perfect version of a thing or we can’t, being stuck in an infinite series.

Also, perhaps we could bite the bullet and suggest that the greatest possible island does exist. However, simply replace “the Lost Island” with “the greatest possible unicorn” or “the greatest possible Santa” to prove other outlandish things.

Or even, consider a retort of my own invention:

14. It is possible for a being to be the greatest possible atheist.
15. Existence is necessary to be the greatest possible atheist.
16. Knowing a conclusive disproof of God is necessary to be the greatest possible atheist.
17. Therefore from 14 and 15, the greatest possible atheist exists.
18. Therefore from 16 and 17, a conclusive disproof of God exists.
19. Therefore from 18, God does not exist.

Super Atheist Man has the super power of being able to disprove God

Exposing the Circular Logic

So how is it that these arguments manage to prove the existence of anything we want them to? It seems to rest with the idea of calling something perfect by definition, and then suggesting existence is part of perfection.

Let’s look at 1-3 again:

1. God is defined to be the greatest possible being.
2. Existence is necessary to be the greatest possible being.
3. Therefore from 1 and 2, God exists.

What happens when we replace “greatest possible being” with what we mean by that term?

1. God is defined to be all-powerful, all-knowing, all-loving, and in existence.
2. Existence is necessary be all-powerful, all-knowing, all-loving, and in existence.
3. Therefore from 1 and 2, God exists.

When we look at this, we see that 1 defines God to exist, and 2 says you must exist to exist, and 3 concludes that therefore God must exist. This is circular: God exists because he is defined to exist. This means we must reject 3 as being logically invalid (also meaning we must reject 11, 16, 17, 18).

It seems that the Ontological Argument is based on circular logic which lurks within the premises, not clearly visible to people reading the argument for the first time. This is why the Argument strikes many people as some sort of magic trick, like you are looking at a mathematical proof that 1 = 2.

This is the bait and switch that makes the argument seem plausible: there are great beings we can imagine and great beings that exist, and that the beings who we can imagine would be greater than the existing ones, should they exist. But we don’t know that they do.

Our concepts of God are thus conditional: if this being were to exist, it would be the greatest possible being. But if it doesn’t, it is just the greatest being among all those we can conceive in our minds, but we will have to look elsewhere to find the greatest possible being.

If existence is a necessary part of being great, we can only search the things we know to exist to find the greatest among them, and that is the greatest possible being.

Finding God in Possible Worlds

Possible worlds are any worlds we can imagine, so basically anything that is logically possible (does not entail a contradiction). To further complicate things, world is used in the expansive sense not in a planetary sense, so perhaps it would be better to say “possible universe”.

Close to anything can be a possible world: a world populated only by monkeys, or a world identical to ours except everyone speaks Spanish, or a world where people are capable of interstellar flight. The only things that can’t be possible worlds are worlds with contradictions, like a world where one does not equal one, or a world with an object that simultaneously has a property and lacks that same property.

Plantinga suggests that we imagine a world with a god in it, a world where perhaps Christianity is true. Such a world appears to be imaginable without contradiction, though if we’re imagining a world like ours, it may imply stubbornly hidden and confusing God that allows people to suffer needlessly, and it couldn’t be a world with prayer.

However, Plantinga is not asking us to imagine any ol’ god, but a greatest possible being, and he thinks that this greatest possible being must possess the property “exists in all possible worlds”. But as soon as we frame the argument like this, we see that Plantinga’s argument is also circular:

5. God is defined to exist in all possible worlds, among other perfect qualities.
6. If a being which exists in all possible worlds exists in any possible world, it must exist in all possible worlds.
7. A being which exists in all possible worlds exists in a possible world.
8. Therefore from 4-7, a being which exists in all possible worlds exists in our possible world.

So Plantinga is really asking us to imagine the existence of “being which exists in all possible worlds”. However, imagining such a being does create contradiction, because we can clearly imagine a world with no such being — a world with nothing at all, or the atheist world. The fact that we can imagine a world with no God means that this God does not exist in all possible worlds.

If this isn’t clear, also imagine a world that contains a “being that destroys all possible worlds” or a “being that if it exists in one possible world, it will prevent consciousness from existing in all worlds”. Like the “being which exists in all possible worlds”, these properties aren’t contradictory on their face, but contradictory to what the idea of a possible world is. Clearly, if these beings existed, we could not exist, but we do.

Thus these beings aren’t even possible, and thus Platinga’s conclusion 8 does not establish the existence of God. And considering Anselm’s and Descartes’s conclusion 3 also ends up unjustified, we can safely rule out the ontological argument as a reason why we should believe in God, and instead look elsewhere.

Those arguments will be left for another day.

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