|Alvin Plantinga, John A. O'Brien Professor of Philosophy at the University of Notre Dame|
Ontological arguments have been around for centuries and began with St. Anselm’s ontological argument. Unlike design arguments and cosmological arguments ontological arguments do not draw upon empirical evidence to prove God’s existence, they use a priori reasoning. One of the more recent and effective versions of the ontological argument is posited by Alvin Plantinga, who is the John A. O'Brien Professor of Philosophy at the University of Notre Dame. His argument can be formulated as follows:
Premise 1--It is possible that a maximally great being exists.
Premise 2--If 1, then there is at least one logically possible world in which a maximally great being exists.
Premise 3--Therefore, there is at least one logically possible world in which a maximally great being exists.
Premise 4--If a maximally great being exists in one logically possible world, it exists in every logically possible world.
Therefore--A maximally great being (that is, God) exists in every logically possible world.
Plantinga defines maximal greatness as a being that is omniscient, omnipotent and all good. Critics of this argument like point out that you could plug anything, like a unicorn, into premise one and have this argument work, but as you think about all possible worlds then this parody doesn’t hold up. For example, a unicorn couldn’t exist in a universe that is hostile to biological life such as a universe that is a million degrees Fahrenheit, or in one where no matter exists. For a being to exist in every possible world it must be a spiritual being with maximal properties.
Not everyone appreciates the non-empirical nature of this argument, but I think that this conceptual argument, when back up by empirically oriented arguments like the cosmological arguments it can be another arrow in the apologist’s quiver.