Final answer:
The Ontological Argument uses a priori reasoning to assert that God exists as 'that than which no greater can be conceived', but critics argue that existence is not a predicate and that the argument could equally prove the existence of the greatest conceivable evil being, leading to logical inconsistencies.
Step-by-step explanation:
The Ontological Argument is a famous philosophical discussion that seeks to prove the existence of God using a priori reasoning, which means reasoning independent of experience and based solely on the concept of God.
The argument posits that if we can conceive of the greatest possible being, then this being must exist both in the mind (intra-mentally) and in reality (extra-mentally), otherwise, we could conceive of an even greater being - one that does exist in reality - which contradicts the initial premise that God is 'that than which no greater can be conceived'.
Critics like Immanuel Kant have challenged this argument by stating that existence is not a predicate; it is not an attribute that can enhance the concept of a being. He argues that existence does not add to the essence of a being, thus the concept of God existing in the mind does not necessitate God's existence in reality.
Additionally, if we follow the logic that allows for defining God into existence, we could similarly define the greatest conceivable evil being into existence, showcasing a flaw in the argument that defeats its premise, as we cannot have two omnipotent beings.
The ontological argument is fascinating and has intrigued philosophers for centuries. Even today, opinions differ on its validity as some philosophers see it as proof of God's existence, while others point out its logical inconsistencies. The ultimate question posed by the Ontological Argument is whether the necessity of God's existence is truly captured by logic and definition or if it remains a matter of faith beyond the scope of philosophical proof.