The Ontological Argument For God's Existence Is Sound

I will be defending Alvin Plantinga's version of the Ontological Argument. For the benefit of those readers unfamiliar with modal logic, I will begin by reviewing the semantics of modal logic's language.Modal Logic SemanticsIn a modal argument, certain words act more like logical operators then they otherwise do in everyday language. Here are the terms that we will be dealing with along with their modal definitions:World – A world is a discrete reality. It does not refer to planets or the cosmos. It simply is a modal term for "what is or can be."Possible World – A possible world is a reality that is logically coherent. A possible world may or may not exist. This is a modal term for "what can be."Actual World – The actual world is our reality, whatever it may be. This is a modal term for "what is." Note that the actual world is also a possible world.Impossible – Something is impossible if it exists in no possible world. Something possible, then, is something that is logically incoherent, like a married bachelor.Possible – Something is possible if it exists in at least one possible world. Something possible, then, is something that is logically coherent.Necessary – Something is necessary if it exists in every possible world. In other words, its non-existence is impossible. Necessary entities are also possible entities.Contingent – Something is contingent if exists in some possible worlds and not others.With these terms under our belt, it's important to also note that when we talk about possible worlds, we are not talking about an infinite number of realities out there in the void. We are talking about descriptions of reality. So, when I say a unicorn exists in some possible world, it does not mean that a unicorn exists in world I (an imaginary world) and does not exist in world A (the actual world) as though these are two separate realities actually bobbing around out there somewhere. What it really means is that I can describe a reality in which a unicorn exists without encountered logical contradictions even though unicorns do not exist in our actual reality. I think this distinction will become important during our rebuttals.GodFor the purposes of this debate, I will define God (modally) as a "maximally great being." A maximally great being is a being which is maximally excellent in every possible world. Maximal excellence includes omniscience, omnipotence, and moral perfection. This is how Alving Plantinga conceived of God for this particular argument. A maximally great being is, by definition, a being for which there is no being greater than itself.ArgumentHere is the argument. I am using "God" in place of "a maximally great being."1. It is possible that God exists.2. If it is possible that God exists, then God exists in some possible world.3. If God exists in some possible world, then it exists in every possible world.4. If God exists in every possible world, then it exists in the actual world.5. If God exists in the actual world, then God exists.6. Therefore, God exists.1. It is possible that God exists.This premise asserts that the aforementioned notion of God is logically coherent. This will be taken as prima facie true until such time as my opponent chooses to contend it.2. If it is possible that God exists, then God exists in some possible world.By virtue of the notion of "possible" in modal logic, if something is logically coherent, then it is possible. This means that we can describe a reality wherein God exists without logical contradiction.3. If God exists in some possible world, then it exists in every possible world.This is proven by the impossibility of the contrary. Any attempt to conceive of a maximally great being that does not exists in every possible world reduces to absurdity. For example, one might argue that a maximally great being exists in the understanding but not in reality. However, such an argument is invalid. Let's take a look:(1) God exists in the understanding but not in reality. (premise)(2) Existence in reality is greater than existence in the understanding alone. (premise)(3) God's existence in reality is conceivable. (premise)(4) If God did exist in reality, then He would be greater than He is. (1 and 2)(5) It is conceivable that there is a being greater than God is. (3 and 4)(6) It is conceivable that there be a being greater than the being than which nothing greater can be conceived. (5 and the definition of "God")As we can see, the attempt to discredit this premise results in contradiction. Any attempt to conceive of maximally great being that does not exist in every possible world ends up proposing simultaneously both a being of which there is no being greater and a being greater than that being.4. If God exists in every possible world, then it exists in the actual world.Since the actual world is within the set of possible worlds, any necessary being exists in it.5. If God exists in the actual world, then God exists.By virtue of the notion of "actual" world in modal logic, this must be the case.6. Therefore, God exists.The conclusion follows inescapably from the premises.ConclusionThe syllogism is logically sound and the resolution is affirmed. I look forward to my opponent's rebuttal.