Plantinga’s version of the Ontological Argument is stated as follows:
- A being is maximally excellent in a possible world if and only if it is omniscient, omnipotent, and morally perfect in that world.
- A being is maximally great in a possible world if and only if it is maximally excellent in all possible worlds.
- There is a possible world in which there exists a being that possesses maximal greatness.
- Therefore, there exists a being that possesses maximal greatness in every possible world.
- Therefore, God exists.
Here we have to deal with possible worlds: hypothetical states of the world that could, in principle, exist, even though they don’t actually exist. There is only one exception: The only possible world that exists is our own world (the actual world).
Plantinga’s Step 1 is to define the properties of a certain being: it must 1) exist in a possible world and 2) it must be omniscient, omnipotent, and morally perfect in that world. He calls this being maximally excellent. Thus far, everything is fine. He’s not asserting from the very beginning that God exists, he’s simply claiming that God exists in a possible (hypothetical) world.
Step 2 of Plantinga’s argument says that if a being meets the conditions of maximal excellency in all possible worlds, it is defined as maximally great. So, for example, if 1) a person called Jack can be shown to exist in all possible worlds, including our own (actual) world, and 2) if Jack is maximally excellent in all of these worlds, then Jack is maximally great.
In Step 3, Plantinga claims that there exists a possible world in which a being like Jack exists – a maximally great being. But there is a problem here: to assume that a maximally great being exists in a given possible world is, by the definition of maximal greatness, to assume that this being exists in all possible worlds. The being could not be called maximally great otherwise.
So, by asserting that there is a possible world in which a maximally great being exists, Plantinga is asserting that this being exists in all possible worlds, including our own. Plantinga is therefore asserting the existence of the very thing he is trying to prove, and the argument fails.
Ultimately, there is no property or characteristic of any being that requires that being to exist in all possible worlds. In other words, there is no logical step to go from the existence of a being in one possible world to the existence of that being in all possible worlds. This highlights what is actually required for the success of the ontological argument: the arguer must proffer a property of his preferred being that necessitates the existence of this being in all possible worlds.
No one has yet to offer such a property. The best attempt I’ve seen is the idea that God is not contingent, namely that his existence does not depend on any particular state of affairs. And if God exists independently of any state of affairs in one possible world, so the argument goes, then he must exist in all possible worlds, since no possible world has conditions that would prevent his existence.
The problem with this argument is that it cuts both ways. If there is no state of affairs that would prevent his existence, then there is also no state of affairs that would necessitate his existence. The existence of God in a given possible world is therefore completely indeterminate. There is nothing we can say about whether God exists in a particular possible world or not, because there are no states of affairs that can be used to predict his presence or absence.
In real life, of course, it seems that everything can be traced to a state of affairs that brought it into existence. This just gives us more reason to be suspicious of the existence of anything that claims to be uncaused. If it has no cause, it probably doesn’t exist.