Gaunilon and Thomas Aquinas opposed, in the Middle Ages, the ontological argument developed by Saint Anselm: it is not because we imagine and design a fortunate island that it necessarily exists, Gaunilon objects in substance.
Similarly, it could be objected that there are many things whose existence nothing prevents and yet do not necessarily exist (or even do not exist at all): monsters, the Father Christmas, flame throwing dragons, Madame Bovary, etc.
Such objections, however, come up against the fact that Anselm’s argument does not speak of any imaginable object, but of that of which nothing greater can be thought of. From this point of view, God is certainly not comparable to an island or to anything finite, replied Saint Anselm.
For Thomas Aquinas, the Anselmian argument is inadmissible because we neither have nor can have innate knowledge of the essence of God. What is said of “God” from the definition of this name is undoubtedly coherent, but it is not enough to prove that a thing corresponding to this name would exist itself. Saint Thomas Aquinas favors demonstrations of the existence of God, but empirical and a posteriori, based on sentient beings, the contingency of the world, its order, etc. : it goes back from creation to God by taking five different paths.
Refutation by Kant
See also the refutation of the ontological argument in the Critique of Pure Reason.
This reasoning is old and cannot be ignored. Kant opposes it not just one, but a whole series of refutations. He begins by tracing this ontological proof from the beginning, questioning how our minds came to the idea of an absolutely necessary being. Kant indeed remarks that no one ever asked this question, taking it for granted:
“[…] this concept which had been risked on the off chance and which finally became completely current, one believed to explain it, moreover, by resorting to a host of examples, so that any subsequent interrogation on its comprehensibility seemed totally useless.”
Kant continues with an example drawn from geometry. When we work on a triangle, we always start by giving ourselves a triangle, and we can then calculate its angles, its sides, etc. If I take a given triangle, I cannot affirm that it has no angles, since by giving myself a triangle, I have established that it has three angles. In short, if I take it as a postulate that this triangle exists, I cannot then destroy it or take away one of its constituent properties. If, however, I want to “remove the triangle along with its three angles, that is not a contradiction.” Alas, humans being lazy, we get tired of saying “For a given triangle, the sum of the angles…” or “For a given triangle, the sum of the two shortest sides…” and we comes to imagine that this triangle exists as an idea in itself. We then imagine that the fact of giving properties to a triangle is a synthesis, that this generates new concepts, whereas in reality we are only noting, in an analytical way, realities that we have posed by the simple evoking this triangle.
“Being is not a real postulate.”
The same goes for the ontological argument. If I say “God is omnipotent,” that is a synthetic judgment. I have in effect taken the concept of God and combined it with the concept of omnipotence. But to say that “God exists” is an analytical proposition since I can derive the concept of existence from the simple analysis of the term God. In other words, “God exists” is a tautology. If I take God as my starting postulate, it will then be impossible for me to remove one of his constituent properties. I cannot posit a concept of God, as I did with the “given triangle” and then say of God that he does not have his property of existence or perfection, any more than I could say of the triangle that it had no angles. But if I suppress the idea of God, I suppress at the same time all its properties: therefore, its existence, its perfection and its omnipotence disappear.
Descartes is therefore correct when he asserts that he cannot conceive of God without existence, if existence is taken as an “added” attribute of God. If I attribute existence to an object, it is indeed absurd to immediately say that this object does not exist. But if one admits that the existence of God follows from the very concept of God, by analysis, then it is possible to deny God and at the same time to suppress all his properties, including existence. We cannot attribute existence to anything. If this were possible, Kant tells us, then a new concept would have to be synthesized from the starting thing and the idea of existence, and then to add existence to this new concept, which would have the effect of create a new one, and so on, ad infinitum. As soon as I think something, it is therefore important that I assume that it exists, at least in my mind. But that’s no guarantee that this thing actually exists.
This argument is not very popular today in its original form (modern thinkers, such as Alvin Plantinga, have developed a modified version of it). In his book Pour ou contre l’Insensé Joseph Moreau defends the validity of the ontological argument. A similar argument developed by Descartes in the third of his Meditations on First Philosophy is that of the “Signature of the Creator” or “Trace of God”. In its ontological dimension, this argument affirms that God has left his mark in us so that we can return to him.
Bertrand Russell rejects the validity of the ontological argument: for him, this argument stems from a logical error: confusion between two distinct orders of predicates: first-order predicates confused with second-order predicates (see the Russell – Copleston debate ).
Gilles Dowek refutes the ontological argument using the correction theorem (reciprocal of Gödel’s completeness theorem).
(Includes texts from Wikipedia translated and adapted by Nicolae Sfetcu)