The ontological argument was formed by Saint Anselm in 1077. It is commonly recognized as being one of the most popular proofs for God’s existence. Descartes also brought the argument back in a different (and more simpler) form as well. Ontology is a branch of metaphysics that deals with the study of existence or being. Thus, the argument is rightly called the ontological argument.
Anselm’s version of this argument go as follows:
(1) Suppose that God exists in the understanding alone.
(2) Given our definition, this means that a being than which none greater can be conceived exists in the understanding alone.
(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 obtains.
(4) But it is greater for a thing to exist in reality than for it to exist in the understanding alone.
(5) Hence we seem forced to conclude that a being than which none greater can be conceived can be conceived to be greater than it is.
(6) But that is absurd.
(7) So (1) must be false. God must exist in reality as well as in the understanding.
Now, (3) and (4) have many problems associated with them. The biggest problem is this: Does the fact that one can conceive of something make it true? To conceive means to form thoughts and ideas. I can conceive many things that do not exist. I can also conceive of them existing in reality. Also, in regards to (4), is existence in reality greater than in the understanding alone? Kant would attack this premise. He said that existence is not a predicate. This means that ideas that exist in the understanding (meaning the mind) are equal to ideas that exist in reality.
As a theist, I would have to accept this criticism against this argument. Our conceptions are only in our minds. Because we can think of things existing in reality does not make them real nor does it make them greater. Ideas with existence as a predicate are still ideas which exist in the understanding.
Descartes’ argument goes like this:
(1) God is a being that has all perfections.
(2) Existence is a perfection.
(3) Therefore, God exists.
Kant would again attack (2). Existence as the predicate to a subject (namely God in this case) does not warrant reality. Also, this version seems to reek of circular reasoning. (2) has the same truth value as the conclusion and thus it is circular. Even if (2) were true, it would be hard to really prove that it‘s true.
Alvin Plantinga has formed a new version of the ontological argument using modal logic.
(1) It is possible that a maximally great being exists.
(2) If it is possible that a maximally great being exists, then a maximally great being exists in some possible world.
(3) If a maximally great being exists in some possible world, then it exists in every possible world.
(4) If a maximally great being exists in every possible world, then it exists in the actual world.
(5) If a maximally great being exists in the actual world, then a maximally great being exists.
(6) Therefore, a maximally great being exists.
A possible world is a way the whole of reality could be and not a set of possible planets. For instance, there could be some possible world in which my name is actually Jim instead of Jesse. There could be a possible world in which McCain is elected President instead of Obama. This concept of possibility applies to this argument. The actual world is defined as the presently existing world. Also simply put, a being which is maximally great is a being with the properties of omniscience, omnipotence, and moral perfection.
This argument really hinges on (1) being true. If (1) is not true then the argument falls flat on its face. If (1) is true (even the mere possibility) then it follows from that that (6) is true. The possibility of maximally great being existing is not impossible. It seems logically coherent unlike say, a married bachelor or a triangle with 18 sides. If this argument succeeds, then it is victorious and actually has more power than former ontological arguments. The reason why the modal version is better is because it does not assume existence is a predicate for perfection. It merely hinges on possibility.
I might revisit this argument in more detail once I study modal logic in the future.