The argument goes like this:
If G-D is that, than which, no greater can be conceived and/or realized, Anselm argues, then nothing can be imagined that is greater than G-D.
If G-D does not exist, though, then something can be imagined, that is greater than G-D, namely a G-D that does exist.
The hypothesis that G-D does not exist thus seems to give rise to a logical absurdity: that there both is and is not something that can be imagined that is greater than G-D.
There is, because it’s possible to imagine a G-D that does exist. There isn‘t, because it’s impossible to imagine something greater than the greatest thing imaginable.
A hypothesis that gives rise to a logical absurdity, though, must be false.
The hypothesis that G-D does not exist, therefore, is false; thus G-D must exist.
There are many obvious problems with this argument, largely available on the internet.
Here's one of my favorites, for your viewing pleasure:
But you know, after giving it some thought, I came to this conclusion:
The Ontological Argument is actually completely ass-backwards!
The argument bases its nearly entire house of cards on the premise that perfect things are those that exist. But if you think about it, it's actually the complete opposite!
Perfection - by definition - DOES NOT EXIST.
What do I mean:
First, we need to define "perfection". What is "perfection"?
Perfection is that which we cannot imagine something better/greater than.
This is the same definition as used in the original argument.
Notice specifically that the word "imagine" is the one being used.
The reason for this is that there's already a different word for the following definition:
"X is that which nothing better than it exists."
That word is: "Best".
However, even if something is "the Best there is", doesn't necessarily mean that it's "perfect". For example:
Let's say that I have the best computer processor in existence. It's the fastest, most efficient etc.. Is it "perfect"? Well, since speed and efficiency are relativistic terms, that means I can always imagine something better. So let's say the processor's speed is X, I can just imagine the same processor with a speed of X+10 for example, and presto: I have imagined a processor which is better than the best processor in existence. Therefore, the best computer processor in existence is NOT perfect (I can imagine something better). Does it mean that this "better" computer processor that I just imagined exist? Of course not, because I started with the premise of "the best computer processor in existence". It's an infinite induction.
As humans, our collective imagination is quite limitless. This means that whatever object we are presented with, we can always imagine something better if we put our minds to it. You can demonstrate it with every conceivable thing and if you think you found a thing which you can't imagine something better than, just present it to someone else until you find someone that thinks of something better.
YES, that includes the Abrahamic God as well. In fact, it's extremely easy to imagine something better, given that the Abrahamic God is arguably one of the worst gods in mythology.
For example: The Abrahamic God created Hell in order to punish the sinners. A better God would somehow turn all sinners into good people, thus not requiring anything as horrible as a Hell. Which is better? Lots of sinners and the existence of eternal torture? Or only good people in existence and no such thing as eternal torture? Obviously it's the latter. I have successfully imagined something which is better than the Abrahamic God, therefore the Abrahamic God is NOT perfect. The Abrahamic God is actually so bad that I can spend all day long thinking about flaws that could be fixed.
We can follow this reasoning to reach the inevitable conclusion:
Perfection, by definition, DOES NOT EXIST.
If you think you found something "perfect" - we can imagine something which is better, hence the "perfect" thing is no longer "perfect". It's now obsolete because there's this other more "perfect" thing which we imagined. And if that other perfect thing somehow comes into existence, we'd be able to imagine something even better. So on and so forth ad nauseum.
So, if in fact you define your God as that which is the most perfect being we can imagine, that would actually lead to the conclusion that God is the complete opposite of existence - which is non-existence.
Therefore, a perfect God, by definition - DOES NOT EXIST.
The Reverse Ontological Argument - Reductio Ad Absurdum Formulation
(1) A perfect being is that which no greater can be conceived.
(2) For every single being in existence, it is possible to imagine a greater being that does not exist.
(3) Let God be a perfect being that exists.
(4) From (2) it follows that we can imagine a greater being which is "more perfect" than God. We reach a contradiction with (3).
(5) Since we can imagine a being which is greater than God, it follows that either the being God is not perfect, or it doesn't exist.
