The Ontological Argument for the existence of God is perhaps one of the least satisfying arguments. I also think it’s one of the most underrated due to its complex and precise use of terms, but in my opinion, is one of the more philosophically powerful once it’s properly understood. Because it is so complex (due to its reliance on precise definitions), it’s often confused with being too simple and therefore not much of an argument.
1. It is possible that a maximally great being exists.
2. If it is possible that a maximally great being exists, then a maximally great being exists in some possible world.
3. If a maximally great being exists in some possible world, then it exists in every possible world.
4. If a maximally great being exists in every possible world, then it exists in the actual world.
5. If a maximally great being exists in the actual world, then a maximally great being exists.
6. Therefore, a maximally great being exists.
I think the most prevalent misstep when considering the weight of the argument is the misunderstanding that maximally = the most possible. This is what leads to the false analogies of maximally perfect islands or whatever. Maximally great, as used for the argument, describes a quality, not a quantity.
So it’s not that God must possess the most of a particular property in order to be maximally great. It’s not that He be the most loving, or the most benevolent, or the most just; it’s that His greatness in those areas cannot be improved upon. He must be perfectly loving, benevolent, and just. For example, I love it when I make a peanut butter and jelly sandwich with the perfect ratio of peanut butter to jelly. The correct amounts of each make for the best sandwich. The entire jar of peanut butter and the entire jar of jelly make for a terrible sandwich. Likewise for God to be maximally great, He need be perfectly just and perfectly benevolent, for example. It is the perfect balance and application of His properties that makes God maximally great, and not the sheer volume of each.