St. Anselm's approach was to define God as, "that than which nothing greater can be conceived". Famed pantheist philosopher Baruch Spinoza would later carry this idea to its extreme: "By God I understand a being absolutely infinite, i.e., a substance consisting of infinite attributes, of which each one expresses an eternal and infinite essence." For Spinoza, the whole of the natural universe is made of one substance, God, or its equivalent, Nature. His proof for the existence of God was a variation of the Ontological argument.

How did St. Anselm define the existence of God?