The ontological argument for the existence of God relies on specific characteristics of God’s nature. In particular, God’s personness and perfect goodness come into play. Let’s begin with God as person.
Theists agree that God is an intelligent, communicative being. God is not only a person, but the perfect model of personhood. God is perfect personness. Consider Plato’s theory of the forms, which asserts that there is a perfect concept of everything that exists. God is the perfect concept of person and all other persons merely participate in the form of person, but without perfection.
Perfection is key. God possesses all the characteristics of personness ad perfectum (to perfection). One of the characteristics of personness is goodness, therefore God is perfectly good. Being perfectly good means God must always do the best thing possible. So, yes, God’s perfection limits him to only doing what is best.
Now, the argument.
Let’s look at the ontological argument as presented in T.J. Mawson’s Belief in God.
P1. God, by definition, is a perfect being.
P2. It is better to exist than not to exist.
∴ God exists.
The argument is good, but skips a few of the steps we discussed above. When we add those steps, the argument becomes more solid.
P1. God, by definition and concept, is a perfect being.
P2. A perfect being is perfectly good.
P3. A perfectly good being must always do what is best.
P4. It is better to exist than not to exist.
P5. God must choose to exist as existence is best.
∴ God exists.
God exists because it is better to exist than not to exist. As a perfectly good being, God must choose that which is best. This video from the Center for Philosophy of Religion offers philosopher Alvin Plantinga’s explanation of the argument.
QED is an acronym for the Latin phrase “Quod Erat Demonstrandum.” It is often used at the end of philosophical and mathematical proofs as it loosely translates to “what was to be shown” or “which was to be demonstrated.” In this use it signifies that that which was sought to be proved has been proven.
Mawson, T.J. Belief in God: An Introduction to Philosophy of Religion. Oxford.