Final answer:
In St Anselm's Ontological Argument, God is defined as 'a being than which nothing greater can be conceived.' The argument is a priori and uses a reductio ad absurdum approach to establish the necessary existence of this greatest conceivable being.
Step-by-step explanation:
The name of God for St Anselm in his Ontological Argument is 'a being than which nothing greater can be conceived.' St Anselm, in his philosophical exploration of God's existence, uses this definition as a foundational concept for his argument. This a priori argument asserts that, because we can conceive of such a greatest being, it must therefore necessarily exist. Anselm's Ontological Argument is not based on empirical evidence but rather on reason and logic, following a reductio ad absurdum approach to demonstrate the existence of God. As part of this logical reasoning, Anselm posits that if we assume the greatest conceivable being does not exist, then we can conceive of a greater being—one that exists both in mind and in reality. This leads to a contradiction, as nothing greater than 'that which nothing greater can be conceived' can exist. Anselm uses this contradiction to show that the greatest conceivable being must exist in reality.