"2. The Ontological Argument Nothing greater than God can be conceived (this is stipulated as part of the definition of "God"). It is greater to exist than not to exist. If we conceive of God as not existing, then we can conceive of something greater than God (from 2). To conceive of God as not existing is not to conceive of God (from 1 and 3). It is inconceivable that God not exist (from 4). God exists. This argument, first articulated by Saint Anselm (1033-1109), the Archbishop of Canterbury, is unlike any other, proceeding purely on the conceptual level. Everyone agrees that the mere existence of a concept does not entail that there are examples of that concept; after all, we can know what a unicorn is and at the same time say, "Unicorns don't exist." The claim of The Ontological Argument is that the concept of God is the one exception to this generalization. The very concept of God, when defined correctly, entails that there is something that satisfies that concept. Although most people suspect that there is something wrong with this argument, it's not so easy to figure out what it is. FLAW: It was Immanuel Kant who pinpointed the fallacy in The Ontological Argument--it is to treat "existence" as a property, like "being fat" or "having ten fingers." The Ontological Argument relies on a bit of wordplay, assuming that "existence" is just another property, but logically it is completely different. If you really could treat "existence" as just part of the definition of the concept of God, then you could just as easily build it into the definition of any other concept. We could, with the wave of our verbal magic wand, define a trunicorn as "a horse that (a) has a single horn on its head, and (b) exists." So, if you think about a trunicorn, you're thinking about something that must, by definition, exist; therefore, trunicorns exist. This is clearly absurd: we could use this line of reasoning to prove that any figment of our imagination exists."