Ontology is the branch of metaphysics that deals with the nature of being.
The classic ontological argument for the existence of God runs as follows:
- God is the greatest imaginable being.
- All else being equal, a being or entity that exists is greater than one that doesn't.
- Therefore, God exists.
In this argument, existence is given as one of God's attributes as part of the definition: if X is God, then X has the property of existence. This is logically equivalent to "if X does not exist, then X is not God." It does not prove that there are any entities that actually match the definition.
Existence can hardly ever be considered a attribute, as something nonexistent cannot have attributes. Therefore, making conclusions about existence of an entity based on its properties is not logically sound.
In short, this argument boils down to "show me a god, and I'll show you an existing god." It is a form of circular reasoning because the existence is built into the assumptions.
Here are some examples of this proof that highlight the fallacy.
- Let us define a unicorn as a magical equine being that has one horn, and that exists.
- By the above definition, such a being must necessarily exist.
- Therefore unicorns exist.
- Shangri-La is the greatest place on earth.
- A place that exists is greater than one that doesn't.
- Therefore, Shangri-La exists.
- Hercules is the greatest warrior in history.
- A warrior that existed is greater than on that did not.
- Therefore, Hercules existed.