The ontological argument is often discarded as a relatively weak proof for the existence for God. While this is true, and some formulations such as Anselm’s can be immediately dismissed, stronger proofs do exist. Alvin Plantinga’s ontological argument is proof of this. Plantinga’s makes use of modality, or possibility, in conjunction with perfection to make his point. Plantinga’s argument has been rephrased several times, so here I will provide a rather clear formulation of it by philosopher William Lane Craig (who I covered earlier on this blog as well).

The first definition Plantinga employs is that of a maximally great being (MGB). The MGB can be thought of as the typical omni-omni God: all knowing and all powerful. Sometimes moral perfection is also included, but for the sake of simplicity, I’ll leave it out of this formulation since it is not explicitly mentioned. Another thing to keep in mind is the definition of “possible worlds.” A possible world is simply a plausible way that things could have been. So for example, if I decided to go on a run at 9 am today instead of at noon, that would be a different possible world. A possible world is one where I ate Thai food last night instead of Italian. It is not, however, a world where 1+1 = 3 or where triangles are round. The latter two examples are logically impossible, and cannot exist in any world.

With those two definition cleared up, we can jump into the key first premise of the argument. Here, Plantinga proposes that “It is possible that a maximally great being exists in world W.” All this is premise states is that an MGB could possibly exist in a world W, not that it is likely or that an MGB actually does exist. This is an important distinction. Next, Plantinga proposes that if a MGB possibly exists, then is must exist in some possible world. Premise two is a neat flip by Plantinga, as he goes from possible existence in one world to assured existence in a possible world. To illustrate this point, think of a carnival game where one attempts to find a red jelly bean. In this game, one needs to select a red jelly bean from a jar filled with other jelly beans. Equivalent to the prior scenario would be a game where 100 or so jars are filled with just one color of colored jelly beans. The player, blindfolded, needs to select the jar containing red jelly beans. Both games are fundamentally the same.

The third premise applies the concept of the MGB to every world. MGB is a maximally great being. Thus, if a being that was maximally great existed in world W but not in world Z, it would not be a maximally great being—just a mostly great being. Since we treat “maximal greatness” as an all or nothing binary, without this property of existence in every world, the being cannot be maximally great. Hence, if a maximally great being exists in some possible world, then it exists in every possible world. Failure of the MGB to do so would be contradictory to the definition of a MGB as a whole.

The last few premises, four to six, simply serve to flush out the proof. Premise four establishes that if an MGB exists in every possible world, it must exist in the actual world. From there, five and six state that if an MGB exists in the actual world, a MGB must exist. In six sentences, Plantinga has seemingly proven the existence of God.

However, while I did state that Plantinga’s argument was stronger than most other ontological arguments, that does not mean it is foolproof. Like most other ontological arguments, Plantinga’s first premise seemingly defines God into existence. The third premise, in particular, relies on this definition: by positing God as an MGB and then postulating existence in all worlds as a trait of maximal greatness, Plantinga practically admits circularity. To commend Plantinga, he does somewhat hedge this by including the concept of possibility in the first premise. Still, circularity significantly detracts from soundness of the argument. For example, one could define into existence a rival being to the MGB, the un-maximal being (UMB). If one simply repeats the same premises used for the MGB with the UMB, they reach an equally convincing argument.

This is a problem. Plantinga’s argument leads us discover a completely contradictory argument and gives us no clear way to decipher which one to believe. Again, Plantinga and other philosophers have attempted to remedy this discrepancy by embellishing the fact that the rival argument does not make the original MGB argument irrational. One can concede that a rational person could plausible accept the first premise that admits to the possibility of an MGB. Yet, a rational person could just as easily accept the rival argument. Thus, Plantinga’s argument lends itself heavily to conformation bias: if one already believes in God, they will have no problem accepting that an MGB plausibly exists, and therefore their convictions will be confirmed in a sound way. The opposite is true as well, meaning the argument accomplishes very little.

A general qualm I have with theological arguments, aside from the irresistible tendency to define God into existence, is the uselessness of them. Don’t get me wrong: I love reading these arguments, but I can’t imagine being convinced into believing in God based off of one of them. To me, it seems that a connection with a higher power cannot be—at least not completely—based on logic. Belief in God, in my opinion, must be a “leap of faith,” a Kierkegaard originally thought.

At our core, humans are arational creatures. I suspect that more often than not, people approach theological arguments with confirmation bias: they accept arguments that support what they already believe and dismiss those that do not. Whether this happens mainly because the arguments themselves are weak or because human reasoning is inherently biased is the real question.