Final answer:
Anselm's ontological proof on God's existence is a priori argument that defines God as 'a being than which nothing greater can be conceived'. It shows that if God only exists in the mind, then a greater being can be conceived, leading to a contradiction. Therefore, God must exist in reality.
Step-by-step explanation:
Anselm's ontological proof on God's existence is characterized as a a priori argument. It does not appeal to empirical or sense data, but rather relies on logical reasoning and conceptual analysis. In this argument, Anselm defines God as 'a being than which nothing greater can be conceived'. He then proceeds to show that if God only exists in the mind, then a greater being can be conceived, which leads to a contradiction. Therefore, God must exist in reality. Anselm's argument is often presented as a Reductio Ad Absurdum, where the assumption that God does not exist is shown to lead to an absurd conclusion, thus implying that God exists.