Ontological argument - Wikipedia

Anselm's ontological argument is a philosophical argument, made from an ontological basis.

Anselm defines God as "the greatest being" and argues that if such being can exist in the mind, then it must also exist in reality. If it existed only in the mind, then an even greater being must be possible—one who exists both in mind and in reality. Therefore, this greatest possible being must exist in reality.

1. Anselm assumes that the greatest possible being must exist in the mind, even in that of the person who denies the existence of God.
2. He also assumes that the greatest possible being must exist in reality.

1. The argument could be used to prove the existence of anything.
2. Humans do not know God's nature.
3. "Existing" adds nothing (including perfection) to the essence of a being. Thus, the greatest possible being does not need to exist.
4. Some attributes of greatness are incompatible with others, rendering the concept of "greatest being" incoherent.