Mailbag: On God's Necessary Existence

James writes, “Hi Randy,

Just a question about the idea of God having a necessary existence: obviously, if God exists, then he couldn't not have existed since (as I understand it) that would mean his existence isn't necessary but merely contingent, and since it's greater for a being to have necessary existence than a contingent one, God must be a necessary being as God, by definition, is a maximally-great being. Now, on thinking all this through, the question which popped into my head was "But why does a MGB have to exist? Why is there such a thing?" Of course, writers often talk about things like "possible worlds" and note that a being that exists in two PWs is greater than one which exists in one, etc., and that a MGB would be one that exists in all PWs and therefore he'd also have to exist in the real world. But then I come to back to why he had to exist? Of course the Ontological Argument hinges on whether the MGB concept is coherent or not and, if it is (and I personally see no problem with it) then a MGB has to exist. But why? Is it because the concept of a MGB is coherent and therefore that is why he has to exist? Or am I missing something?. Hope that makes sense?”

Randy responds, “Hi James,

First, we have to distinguish the type of necessity the MGB must have. It is the property of necessary existence in his very being or nature/essence itself. We would say of God, "God necessarily exists." This is called de re necessity. So, strictly speaking, the answer to the question "Why does God have to exist?" is "Because he has necessary existence." So then it can be asked why God has the property of necessary existence, but it seems you answered that question by correctly pointing out that a God who exists in only some possible worlds is not as metaphysically great as the God who exists in all of them. That is to say, necessary existence is what is called a great-making property, a property that it is better to have for a being than to lack. So then the answer finds a terminus in this logic.

I suspect, however, that you're not asking why God must exist, but why it follows from God's mere possibility that he exists in reality (and thus the "must" language: it is the necessity of the entire argument; it must be the case that if all of the premises are true then the conclusion is true). Let's demonstrate one version of the Modal Ontological Argument (MOA):

1. It is possible that a Maximally Great Being (MGB) exists.

2. If it is possible that MGB exists, then MGB exists in some possible world.

3. If MGB exists in some possible world, then he exists in all of them.

4. If MGB exists in all possible worlds, then he exists in the actual world.

5. Therefore, MGB exists in the actual world.

6. Therefore, MGB exists.

(1) relies on our modal intuitions. We think it is possible, at least initially, that an unsurpassably great being exists than which no greater can be conceived (Anselm's formulation). For MGB theorists, this is a being that possesses all compossible (meaning possible together) great-making properties exemplified to the intrinsic maximum, where such properties admit of degrees. (2) just points out that if it's possible, we can say MGB exists in a possible world. A possible world is a way of representing how reality could have been. However, we can see that, on reflection, a being who truly is the MGB will have the property of necessary existence. Why? Because, quite simply, it's metaphysically better for a being to have the property of necessary existence than to lack it (3). Think about a being identical to God in every other respect who nonetheless only exists in a few million possible worlds. He would not exist in many billions of possible worlds. Or even suppose there is a God who is just like MGB who exists in every possible world save one. MGB would exceed them all, because he would have all of their power and be present in every possible world. That brings us to (4). The actual world is a possible world because the actual world is a way reality could have been (if not, it wouldn't be actual!). So since the actual world is numbered up with the set of possible worlds, and if MGB exists in all possible worlds, then by the rules of logic the MGB exists in the actual world, which of course means he actually exists! Let's look at these if-then premises in a different order:

2. If it is possible that MGB exists, then MGB exists in some possible world.

3. If MGB exists in some possible world, then he exists in all of them.

4. If MGB exists in all possible worlds, then he exists in the actual world.

1. It is possible that a Maximally Great Being (MGB) exists.

7. Therefore, MGB exists in some possible world.

8. Therefore, MGB exists in every possible world.

5. Therefore, MGB exists in the actual world.

6. Therefore, MGB exists.

So, we can see that the rules of logic necessitate the conclusion that God exists. I hope this at least frames the issues for you in a helpful way!”