Perhaps the most "beautiful" and philosophically appealing of all the rational arguments is the Ontological Argument. The argument contends first that the term "God" evokes the idea of the greatest conceivable being possible. In short, God by definition is the "unsurpassable one." A necessary being surpasses one who is not necessary. Therefore, "God" must exist. The argument centers upon the concept of God as the "unsurpassable" one. As such, God is perfect. "Perfection" requires both conception and existence. For God not to exist would make God less than perfect. Therefore, God must exist. To conceive of God as "perfect" and not existing would be self-contradictory. Consequently, God's existence is required by definition.
The argument was proposed by Saint Anselm (1033-1109). Anselm's purpose in constructing the argument lay not in the demonstration of God's existence but in an attempt to establish that all "rational creatures" will conclude that God exists from the very idea or concept of "God." Whereas his successor, Aquinas, built his system upon the work of Aristotle, Anselm established his system upon the teaching of Aristotle's teacher, Plato. Anselm therefore drew from Plato's apriori epistemology whereas it will be remembered that Aristotle's argument was aposteriori. In addition, Anselm was thoroughly influenced by the work of Augustine (354-430) who was influenced by the Neo-Platonist St. Ambrose under whose influence Augustine was converted to Christian faith. Aquinas rejected the Ontological argument since in his view it constituted a violation of inductive logic (Aristotle). Consequently, the Ontological argument has been generally disregarded by Catholic theology and philosophy as methodologically inadequate.
Objection: The ontological argument, while appealing and even containing a great degree of philosophic beauty and appeal is not without weaknesses.
1) The first criticism of the Ontological argument addresses the first premise of Anselm's argument, namely that God is by definition the greatest conceivable being one can imagine. Critics contend that this premise from the start assumes God's existence. It should be said that it appears that there may be validity to this criticism and that this objection is contained in Anselm's intention for the argument in that Anselm believed that the existence of God is in reality a "given" in our self -conscious experience. (Newport, Ultimate Questions, 450)
2) The second criticism addresses the second premise of the ontological argument, which, according to the objection, makes the leap from concept to existence. Anselm's contemporary Gaunilo countered the argument by proposing that that an idea in the mind must also have its counterpart in reality. Concept does not require or necessitate existence. For instance, one can posit the idea of the perfect island. On this island the weather is always the perfect temperature, never too hot, never too cold. On this island, the breeze is always perfect, the Margarita's (or the Captain and coke, whichever is your preference; after all, the island is perfect) are always blended to perfection, the appearance of the opposite sex is perfectly appealing and the water is perfectly beautiful. However, to conceive of such an island does not necessitate its existence. Anselm's counter proposal was that while Gaunilo's argument possessed validity, Anselm's argument was never intended to validate the existence of all concepts with the quality of existence but only of one object, that of God.
3) Finally, to accept the conclusion of the Ontological Argument still tells us nothing about the nature of the "God" whose existence has been proven by the argument.
