This post is one of a serious that picks apart the arguments for god that can be found at the link below. This post addresses number 13:
If you don’t want to click over there to read it, the full argument goes like this:
13. The Ontological Argument
The ontological argument was devised by Anselm of Canterbury (1033-1109), who wanted to produce a single, simple demonstration which would show that God is and what God is. Single it may be, but far from simple. It is, perhaps, the most controversial proof for the existence of God. Most people who first hear it are tempted to dismiss it immediately as an interesting riddle, but distinguished thinkers of every age, including our own, have risen to defend it. For this very reason it is the most intensely philosophical proof for God’s existence; its place of honor is not within popular piety, but rather textbooks and professional journals. We include it, with a minimum of discussion, not because we think it conclusive or irrefutable, but for the sake of completeness.
It is greater for a thing to exist in the mind and in reality than in the mind alone.
“God” means “that than which a greater cannot be thought.”
Suppose that God exists in the mind but not in reality.
Then a greater than God could be thought (namely, a being that has all the qualities our thought of God has plus real existence).
But this is impossible, for God is “that than which a greater cannot be thought.”
Therefore God exists in the mind and in reality.
Question 1: Suppose I deny that God exists in the mind?
Reply: In that case the argument could not conclude that God exists in the mind and in reality. But note: the denial commits you to the view that there is no concept of God. And very few would wish to go that far.
Question 2: Is it really greater for something to exist in the mind and in reality than in the mind alone?
Reply: The first premise of this argument is often misunderstood. People sometimes say: “Isn’t an imaginary disease better than a real one?” Well it certainly is better—and so a greater thing—for you that the disease is not real. But that strengthens Anselm’s side of the argument. Real bacteria are greater than imaginary ones, just because they have something that imaginary ones lack: real being. They have an independence, and therefore an ability to harm, that nothing can have whose existence is wholly dependent on your thought. It is this greater level of independence that makes them greater as beings. And that line of thinking does not seem elusive or farfetched.
Question 3: But is real being just another “thought” or “concept”? Is “real being” just one more concept or characteristic (like “omniscience” or “omnipotence”) that could make a difference to the kind of being God is?
Reply: Real being does make a real difference. The question is: Does it make a conceptual difference? Critics of the argument say that it does not. They say that just because real being makes all the difference it cannot be one more quality among others. Rather it is the condition of there being something there to have any qualities at all. When the proof says that God is the greatest being that can be “thought,” it means that there are various perfections or qualities that God has to a degree no creature possibly could, qualities that are supremely admirable. But to say that such a being exists is to say that there really is something which is supremely admirable. And that is not one more admirable quality among others.
Is it greater to exist in reality as well as in the mind? Of course, incomparably greater. But the difference is not a conceptual one. And yet the argument seems to treat it as if it were—as if the believer and the nonbeliever could not share the same concept of God. Clearly they do. They disagree not about the content of this concept, but about whether the kind of being it describes really exists. And that seems beyond the power of merely conceptual analysis, as used in this argument, to answer. So question 3, we think, really does invalidate this form of the ontological argument.
Charles Hartshorne and Norman Malcolm developed this version of the ontological argument. Both find it implicitly contained in the third chapter of Anselm’s Proslogion.
The expression “that being than which a greater cannot be thought” (GCB, for short) expresses a consistent concept.
GCB cannot be thought of as: a. necessarily nonexistent; or as b. contingently existing but only as c. necessarily existing.
So GCB can only be thought of as the kind of being that cannot not exist, that must exist.
But what must be so is so.
Therefore, GCB (i.e., God) exists.
Question: Just because GCB must be thought of as existing, does that mean that GCB really exists?
Reply: If you must think of something as existing, you cannot think of it as not existing. But then you cannot deny that GCB exists; for then you are thinking what you say cannot be thought—namely, that GCB does not exist.
Possible Worlds Version
This variation on the modal version has been worked out in great detail by Alvin Plantinga. We have done our best to simplify it.
Maximal excellence: To have omnipotence, omniscience and moral perfection in some world.
Maximal greatness: To have maximal excellence in every possible world.
There is a possible world in which there is a being (X) with maximal greatness.
But X is maximally great only if X has maximal excellence in every possible world.
Therefore X is maximally great only if X has omnipotence, omniscience and moral perfection in every possible world.
In W, the proposition “There is no omnipotent, omniscient, morally perfect being” would be impossible—that is, necessarily false.
But what is impossible does not vary from world to world.
Therefore, the proposition, “There is no omnipotent, omniscient, morally perfect being” is necessarily false in this actual world, too.
Therefore, there actually exists in this world, and must exist in every possible world, an omnipotent, omniscient, morally perfect being.
A more lengthy telling of the argument (if you want it) is here: http://www.iep.utm.edu/ont-arg/ and here: https://plato.stanford.edu/entries/ontological-arguments/
In summary, because it is possible to think that there is nothing that is greater than the Christian god, the Christian god is the greatest thing ever and is therefore real. Well colour me unimpressed because I am pretty sure that I can think of a god eating monster that eats gods for fun, especially gods which are greater than those which exist only in the mind. Therefore my god eating monster just ate all the gods so there’s none left. The end.
Jesting aside, this argument is all about the limits of the human mind. The argument posits that the no human can imagine anything greater than X and because something existing is greater than something imagined, the imagined Christian god must be real. The argument makes no allowance for someone else thinking of something greater than the Christian god, there really is nothing about this argument that makes any sense.
I take issue with the phrase ‘philosophical proof’ at the start because I dispute that philosophy can prove any such thing using arguments like this. Proof would be a demonstration of that god that is unambiguous and could not be attributed to anything else. Thinking it real and claiming that that means it is real is not a proof for anything and it is disingenuous to suggest otherwise.
Getting into the grit of the argument itself, it stumbles massively when it says that god must exist both in thought and reality because it’s not possible to think of something greater. It’s a blunt assertion with no support. It is always possible to think of something greater and it is the utmost arrogance to think that because you have imagined in your mind what you think is the greatest possible god, that that god must therefore exist. Thinking something is real doesn’t make it real.
The argument also seems to be implying that when something that exists is thought about, that something exists both in reality and in the mind! No it doesn’t. What is in the mind is simply a mental representation. Like a photocopy isn’t the real thing and it’s copy and a reflection isn’t the real thing and it’s copy.
The argument really does back flip itself into a knot of nonsense.
The argument certainly is imaginative, I’ve got to give it that, but what it imagines isn’t real and the leap from the imagined greatest ever god to that god being real is missing a great many steps and it does not follow in the slightest.