There has been much ado about the ontological argument, most of it skeptical. In response to the chorus of incredulity, it may help to put this into a more formalized type of argument. However, doing so is risky given the sharp minds out there waiting to trip me up. But I care more about corporate illumination than personal vindication so I’ll stick my neck out by trying my shaky hand at unpacking a form of the ontological argument for pedagogical purposes and your critical scrutiny.
Come, let us reason together.
(1) The most perfect being is the being with the maximal number of compossible great-making attributes.
This first premise is merely defining what the concept of a most perfect being is. As I have already noted, the notion of a great-making attribute is objective. All things being equal it really is better to be an agent than a non-agent, to have knowledge rather than to lack it, to have power rather than to lack it, to have goodness rather than to lack it. Based on this kind of intuitive reflection we can build step-wise toward the concept of a most perfect being.
Keep in mind as well the term compossibility. For example, it is better to have free will than not. But whatever freedom the most perfect being will have must be compossible with its other great-making attributes. If omnibenevolence and necessary existence are considered among the being’s great-making attributes, then free will cannot be understood to include the ability to do evil actions or to existingush oneself.
(2) It is possible that the most perfect being exists (that is, there is at least one possible world in which the most perfect being does exist).
This is a modest claim which is based on the fact that there is no contradiction with the notion of a most perfect being.
(3) All things being equal it is greater to exist necessarily than contingently.
Greatness is inherently linked to existence because if something doesn’t exist then it cannot be great. And if two things exist but one has a much more secure purchase on existence than the other, then all things being equal it is greater. The little pig’s house of brick is, all things being equal, greater than the other little pig’s house of straw.
If you don’t like the little pigs’ houses then think of three warriors:
Percy: a former plow boy who would die from one-on-one combat with a chipmunk.
Roland: a burly warrior who could only be killed by the largest dragon in the land.
Maxentius: a massive immortal who cannot be killed by any other creature.
Given these descriptions, Maxentius is greater than Roland and Roland is greater than Percy. And if there were a fourth warrior who were (per impossibile) immortal across possible worlds and not just in the actual world, then that warrior would be even greater than Maxentius.
(An aside: why is it impossible for there to be a warrior immortal across possible worlds? Because warriors are material objects and no material object exists across possible worlds since it is possible that there be no material things at all.)
So we can distinguish some differentiation of greatness or excellence among things that are more stable, secure or long lasting in the actual world. And we can also distinguish between a higher greatness extending to existence across possible worlds.
With that in mind, it is time to introduce our fourth warrior. While Maxentius is immortal in the actual world, he doesn’t exist in some other worlds and thus he is contingent. But our fourth warrior, named “Giganticus”, is not only immortal in the actual world but also across possible worlds. Thus, just as Maxentius is greater than Roland because he is immortal but Roland is not, so Giganticus is greater than Maxentius because he is immortal not only in the actual world but across possible worlds while Maxentius is not.
Here’s one more way to explain that great-making intuition of necessity. Think about possible worlds as analogous to Ferraris. Now ask yourself, what is the greatest Ferrari collection possible? Easy! The one that has all the Ferraris ever made. Likewise, what is the greatest kind of existence (all things being equal)? Easy! The one where the individual exists in every possible world.
(4) The property of existing necessarily is compossible with other great-making attributes.
In other words, necessary existence gets a trump card in any potential conflict with other attributes. Nor is this arbitrary, because if an agent doesn’t exist in a possible world then none of their other attributes can be exemplified either. Think of it like this: the chassis of the car is more important than the paint, seats or steering wheel. In an analogous (but obviously much more radical) way, attributes like omnipotence, freedom and the like are dependent on existence.
Thus omnipotence and free will cannot be understood to mean that God could will his own non-existence in some possible worlds.
Here’s one more illustration: a perfect marriage could never end in divorce. Likewise, the perfect agent could never, by definition, “divorce” itself from existence.
(5) Therefore, the most perfect being exemplifies the property of existing necessarily.
Not much to say here. This just follows necessarily from (1)-(4).
(6) Therefore, there is at least one possible world in which the most perfect being exemplifies the property of existing necessarily.
Ditto. This follows from (5).
(7) If a being exemplifies the property of existing necessarily in one possible world then that being exists in all possible worlds.
This is merely definitional. It is explaining what the concept of necessity means. In other words, to say a being exemplifies the property of existing necessarily in one world just is to say that that being exists in all possible worlds.
(8) Therefore, the most perfect being exemplifies the property of existing in the actual world.
Again, this follows necessarily from (6) and (7).
(9) God is the most perfect being.
As Anselm rightly recognized, this is a matter of definition.
(10) Therefore, God exists.