Nobody's claiming the argument proves THIS...Ontological arguments seek to prove the existence of God simply by armchair reasoning - by thinking through concepts logically rather than venturing out into the world to find material evidence. Ontological arguments usually start from a definition, from which the existence of the entity logically follows. Here is one example:By definition, God is a supremely great existent beingTherefore, God exists.The argument is valid (see previous post). However, is it convincing? No. This is because only somebody who is independently prepared to admit the conclusion (2) will accept the premise (1). Therefore, we would say that the argument is ‘circular’, since the acceptability of the premise depends on whether we already believe the conclusion. Or rather, the argument assumes its own conclusion. Though valid, the argument doesn’t prove anything (though this guy might disagree).Consider a more sophisticated version, attributed to St. Anselm of Canterbury (1033 - 1109):God is the greatest conceivable beingIf something is the greatest conceivable being, it possesses all great-making propertiesA great-making property is a property that, if had, makes a being greaterExistence is a great-making propertyTherefore, the greatest conceivable being possesses the property of existenceTherefore, God possesses the property of existenceTherefore, God existsThis new argument is valid. But is it sound, and therefore convincing to any degree? Though it is thought fashionable these days (mostly to people who haven’t studied any philosophy) to simply declare this argument absurd and walk away, this isn’t a rationally acceptable thing to do - reasons must be given for why an argument is unsound before we reject it.The problem is that this argument cannot so obviously be declared false as the first one, since it is not so obviously circular. It’s all very well to assert ‘you can never define something into existence’, but this isn’t really pointing out a specific flaw in the argument, which is a harder task than many think. Whether this version of the Ontological Argument is good or not, it poses an interesting logical problem nonetheless, and has premises to which even the atheist can agree. Unfortunately, accepting the conclusion renders atheism incoherent.I love ontological arguments - if you give them a chance (which you should), they are endlessly fascinating. More to come on this topic.

read more: The Ontological Argument for God's existence