ontological argument

noun Philosophy.

1. an a priori argument for the existence of God, asserting that as existence is a perfection, and as God is conceived of as the most perfect being, it follows that God must exist; originated by Anselm, later used by Duns Scotus, Descartes, and Leibniz.

noun philosophy

1. the traditional a priori argument for the existence of God on the grounds that the concept itself necessitates existenceCompare cosmological argument, teleological argument
2. any analogous argument from the nature of some concept to the existence of whatever instantiates it