Ontological Argument Most people have not witnessed or experienced God and therefore are confused about its existence. In Western theology, three theories have emerged to demonstrate the existence of God. These theories are the ontological argument, the cosmological argument, and the teleological argument. St. Anselm of eleventh century, and Descartes of seventeenth century, have used the ontological argument for proving the existence of God. The God, for them, is supreme, "needing nothing outside himself, but needful for the being and well-being of all things." (Pg. 305). St Anselm's account of the ontological argument for the existen