We’re using the book “Handbook of Apologetics” by Peter Kreeft and Ronald Tacelli to go over the arguments for the existence of God. Dr. Kreeft teaches logic in two major universities, so his arguments tend to be clear, concise and very helpful.
This week we’ll look at the Possible Worlds version of the Ontological Argument:
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.
Definitions:
Maximal excellence: To have omnipotence, omniscience and moral perfection in some world
Maximal greatness: To have maximal excellence in every possible world.
1. There is a possible world (W) in which there is a being (X) with maximal greatness.
2. But X is maximally great only if X has maximal excellence in every possible world.
3. Therefore X is maximally great only if X has omnipotence, omniscience and moral perfection in every possible world.
4. In W, the proposition “There is no omnipotent, omniscient, morally perfect being” would be impossible—that is, necessarily false.
5. But what is impossible does not vary from world to world.
6. Therefore, the proposition, “There is no omnipotent, omniscient, morally perfect being” is necessarily false in this actual world, too.
7. Therefore, there actually exists in this world, and must exist in every possible world, an omnipotent, omniscient, morally perfect being.
Kreeft, P., & Tacelli, R. K. (1994). Handbook of Christian apologetics: hundreds of answers to crucial questions (pp. 71–72). Downers Grove, IL: InterVarsity Press.