The Ontological Argument is a strange bit of reasoning formulated by the bishop Anselm of Canterbury (now a Saint) in the 11th century.
Paraphrased for brevity, the argument is as follows:
(1) Suppose that God only exists in our minds, merely as an idea and not as a real being.
(2) Given our definition, this means that a being than which none greater can be conceived exists only in our minds.
(3) But this being can be conceived to exist in reality. That is, we can conceive of a circumstance in which theism is true, even if we do not believe that it actually is true.
(4) But it is greater for a thing to exist in reality than for it to exist only in the mind.
(5) Hence we seem forced to conclude a contradiction: that a being than which none greater can be conceived can be conceived to be greater than it is.
(6) But that is a direct contradiction and therefore impossible.
(7) So (1) must be false. God must exist in reality as well as in the understanding.
Note that in my responses I will use the abbreviation ‘GCB’ to refer to the term ‘Greatest Conceivable Being’.
1. The OA reveals no contradiction in the non-existence of a Greatest Conceivable Being
Anselm’s claims that the GCB (what we would call “God”) is defined as a being that is maximally powerful, knowledgeable, benevolent, and exists, since he argues that existing is a quality that renders a being greater than it would otherwise be.
Even if we accepted all of Anselm’s assertions regarding what would mean for a being to be the “greatest conceivable”, his argument would still fail.
This is simply because Anselm’s Premise 5 reveals no contradiction since his Premise 4 only shows that the concept of a GCB introduced in Premise 3 would be the only coherent definition of a GCB according to his notion of greatness. It only means that under these definitions, we could only label an existing being as a GCB, but it does not in any way pertain to whether a being with a GCB’s other qualities exists in actuality.
That’s all. It’s hardly a remarkable point.
2. Existing is not a factor that affects a thing’s definition
By insisting that a being’s defining qualities – in this case, the vague notion of “greatness” – Anselm is treating existence as a property of its own, the presence, absence, or degree of which alters its definition.
But the nature and qualities of a being is matter of concept definition with no regard to its actual state of existence. This is because the concept of existence describes whether a another concept’s defining qualities have a match in reality.
This means Anselm’s argument fails in Premise 4 since it attempts to apply the concept of existence in a way that is nonsensical.
Now my point here is not unique. I am merely presenting it on my site as a concise refutation that is stated in a way that is quicker to absorb and understand than the more verbose and elaborate explanations of the same point by historical philosophers.
The most famous critic of the OA was Immanuel Kant, who, despite believing in God, rejected the logic of the OA, He and others pointed out that existence is not a intrinsic quality that defines a thing; it has no relevance to its nature or character, and thus cannot be claimed as an intrinsic attribute that can present a contradiction in definition if the entity doesn’t actually exist.
Additional notes on the Ontological Argument:
Does the OA Beg the Question?: The OA may initially appear to commit the fallacy of Begging the Question but it actually does not. The conclusion is not assumed in the premise. The argument just tries to use definitions to prove that we would be faced with a contradiction between definitions if God did not exist. The OA instead makes the error I described.
“Greatness” is a vague and subjective term in this context”: The use of the term “greatness” to describe a defining quality of a being is problematic because “greatness” refers to subjective and relative notions or to measures of objective factors. Greatness cannot be treated as a quality of its own that could be possessed by an entity. To do so renders it vague and meaningless, and therefore the qualities attributed to a GCB are arbitrary and cannot form the basis of an objective point about the existence of a being. In order to keep my points on this page restricted to my most direct objection to the OA, I will later place these additional points to a separate, supplemental article devoted to that subject alone.
The Problem of Evil: I view the Problem of Evil as evidence that blatantly contradicts the possibility of God as defined by Anselm. You can read my arguments in favor of this view and my responses to objections against it in the article at this link.
I have placed this objection in this section rather than listing it as a primary flaw of the OA because the meaning of terms such as “goodness”, “moral perfection”, “omnibenevolence, or being “perfectly good” used in the definition of God are defined in different ways by different Theists, and sometimes not defined at all. And since the Problem of Evil is only relevant to the concept of a deity that wishes to reduce the suffering of other beings, not all definitions of moral goodness, the Problem of Evil cannot be said to apply to all forms of the OA.