Ontological argument

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:

1. God is the greatest imaginable being.
2. All else being equal, a being or entity that exists is greater than one that doesn't.
3. Therefore, God exists.

Counter-arguments

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.

Unicorns:

1. Let us define a unicorn as a magical equine being that has one horn, and that exists.
2. By the above definition, such a being must necessarily exist.
3. Therefore unicorns exist.

Shangri-La:

1. Shangri-La is the greatest place on earth.
2. A place that exists is greater than one that doesn't.
3. Therefore, Shangri-La exists.

Hercules:

1. Hercules is the greatest warrior in history.
2. A warrior that existed is greater than on that did not.
3. Therefore, Hercules existed.