RF & AA: The Ontological Argument

The Ontological argument is one of the most interesting arguments for God’s existence. In Reasonable Faith William Lane Craig supports Plantinga’s formulation of the argument. The Ontological argument tries to show that God exists necessarily by definition, so not only does he exist but one would contradict themselves by saying God does not exist.

It is rather important to understand the logic of possible worlds as Plantinga’s employs them. Possible worlds as I understand them are logical possibilities—not only that they contain every logical proposition or their negation.  Craig somewhat helpfully explains them somewhat like this: A possible world is a conjunction which compromises every proposition or their negation. So we have propositions p,q,r,s…. These propositions are simply statements that refer to logical possibilities so you could fill them with any logical possibility you can imagine. Now the set of possible worlds would contain every proposition or their negation so in the case of our set they would look something like this:

Possible World₁:p,q,r,s…

Possible World₂:p,-q,r,s…

Possible World₃:p,q,-r,s…

Possible World₄:p,q,r,-s…

Hopefully I have explained possible worlds in a somewhat understandable fashion. Now according to S5 logic if it is possible that God exists in some possible worlds he must exist in all of them, including the actual world (the one we inhabit). Because if God exists only in some possible worlds then he is contingent, that is he could or could not exist in a possible world. But since God is necessary he in not contingent and therefore he must exist in every possible world. Perhaps you can already see one of the glaring problems with this argument, it appears to be begging the question. Anyway leaving that aside. Plantinga describes God as a maximally great being, one which has all the great making properties (omnipotence, omniscience, moral perfection). Here is the formal version of it:

           

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.

Now Le Poideving in Arguing for Atheism builds a similar argument but with a different conclusion:

1. It is possible that a maximally great being does not exist.

2. If it is possible that a maximally great being does not exist, then a maximally great being does not exist in some possible world.

3. If a maximally great being does not exist in some possible world, then it does not exist in the actual world.

4. If a maximally great being does not exist in the actual world, then a maximally great being does not exist in the actual world.

5. Therefore, a maximally great being does not exist.

Or at least he says something vaguely along these lines. Because of this simple turn of events it would appear that the Ontological argument is not the greatest argument for God’s existence. There is still much to say on this argument but I will leave you on this happy note.

Craig, William L. Reasonable Faith: Christian Truth and Apologetics. 3rd ed. Vol. 1. Wheaton, IL:      Crossway Books, 2088. N. pag. 1 vols. Print.

Le Poidevin, Robin. Arguing for Atheism: An Introduction   to the Philosophy of Religion. London: Routledge, 1996. N. pag. Print.